LIBRARY UNIVERSITY OF CALIFORNIA. JAN 16 1893 ^Accessions No. G~&~$lL ,. Class Series of /IDofcern Jpbilosopfoers. Edited by E. Hershey Sneath, Ph.D. DESCARTES by PROF. H. A. P. TORREY of the University of Vermont.* SPINOZA by PROF. GEO. S. FULLERTON of the University of Pennsylvania.* LOCKE by PROF. JOHN E. RUSSELL of Williams College.* BERKELEY by EX-PRESIDENT NOAH PORTER of Yale University. HUME by PROF. H. AUSTIN AIK1NS of Trinity College, N. C. REID by E. HERSHEY SNEATH of Yale Uni- versity.* KANT by PROF. JOHN WATSON of Queen's University, Canada.* HEGEL by PROF. JOSIAH ROYCE of Harvard University. * Those marked with an asterisk are ready HENRY HOLT & CO., PUBLISHERS, NEW YORK. Series of flftobern fcbilosopbers ,Edited by E. Hershey Sneath, Ph.D. THE PHILOSOPHY OF REID it AS CONTAINED IN THE "INQUIRY INTO THE HUMAN MIND ON THE PRINCIPLES OF COMMON SENSE" WITH INTRODUCTION AND SELECTED NOTES BY E. HERSHEY SNEATH, PH.D. Instructor in Philosophy in Yale University NEW YORK HENRY HOLT AND COMPANY 1892 15/5-3 _T3 COPYRIGHT, 1892, BY HENRY HOLT & CO. PREFACE. AFTER careful consideration, it seemed better to me, and, at the same time, to be consistent with the idea of the " Series" of which this book is a member, to present Reid's Philosophy in an edition of the " In- quiry," rather than in a book of extracts taken from the " Inquiry" and the " Intellectual Powers." The substance of Reid's Philosophy is contained in his theory of perception and his doctrine of common sense. Herein, too, lies his historical significance. The " Inquiry" contains all that is essential for an understanding of Reid's views on these subjects, and presents it in a comparatively brief form. By omit- ting Sees. IX-XIX (pp. 199-287), which can be easily spared,- the subject-matter will be brought within the limits prescribed by the " Series. " The sections re- ferred to above will be found interesting, especially when studied in connection with Berkeley's famous *' Theory of Vision," hence their retention. The text of this edition is taken from Sir Wm. Hamilton's seventh edition of Reid's Works (Edinburgh, 1872). The most important notes of Hamilton, as well as his Index, abridged, have been retained. The " Inquiry" affords an inviting field for criticism, but the limits of the Introduction forbade my entering upon it. E. H. S. iii CONTENTS. PAGE BIOGRAPHICAL SKETCH. i BIBLIOGRAPHY 7 RELATION OF REID'S PHILOSOPHY TO ITS PHILOSOPHICAL ANTECEDENTS u THE INFLUENCE OF REID'S PHILOSOPHY UPON SUBSEQUENT PHILOSOPHIC THOUGHT 47 AN INQUIRY INTO THE HUMAN MIND. DEDICATION 65 CHAPTER I. INTRODUCTION. Section I. The Importance of the subject, and the Means of prosecuting it 70 II. The Impediments to our knowledge of the mind.. 72 III. The Present State of this part of philosophy. Of Descartes, Malebranche, and Locke 76 IV. Apology for those philosophers 80 V. Of Bishop Berkeley; the "Treatise of Human Nature" ; and of Scepticism , 81 VI. Of the ' ' Treatise of Human Nature" 84 VII. The system of all these authors is the same, and leads to Scepticism 86 VIII. We ought not to despair of a better 87 CHAPTER II. OF SMELLING. Section I. The Order of proceeding. Of the medium and organ of Smell 89 II. The Sensation considered abstractly 90 III. Sensation and Remembrance, natural principles of Belief 92 v VI CONTENTS. PAGE Section IV. Judgment and Belief in some cases precede Sim- ple Apprehension 95 V. Two Theories of the Nature of Belief refuted. Conclusions from wfiaThath been said 96 VI. Apology for metaphysical absurdities. Sensa- tion without a sentient, a consequence of the theory of Ideas. Consequences of this strange opinion 99 VII. The conception and belief of a sentient being, or Mind, is suggested by our constitution. The notion of Relations not always got by Com- paring the related ideas 105 VIII. There is a quality or virtue in bodies, which we call their Smell. How this is connected in the imagination with the sensation. . . 109 IX. That there is a principle in human nature, from which the notion of this, as well as all other natural virtues or causes, is derived in X. Whether in Sensation the mind is Active or Passive 116 CHAPTER III. OF TASTING 118 CHAPTER IV. OF HEARING. Section I. Variety of Sounds. Their place and distance learned by Custom, without reasoning 122 II. Of Natural Language 124 CHAPTER V. OF TOUCH Section I. Of Heat and Cold 129 II. Of Hardness and Softness 131 III. Of Natural Signs 135 IV. Of Hardness, and other Primary Qualities 139 V. Of Extension 141 VI. Of Extension 144 VII. Of the existence of a Material World 148 VIII. Of the Systems of Philosophers concerning the Senses 156 CONTENTS. CHAPTER VI. OF SEEING. Section I. The excellence and dignity of this faculty 162 II. Sight discovers almost nothing which the Blind may not comprehend. The reason of this 164 III. Of the Visible Appearances of objects 169 IV. That Colour is a quality of bodies, not a sensation of the mind 173 V. An inference from the preceding 177 VI. That none of our sensations are Resemblances of any of the qualities of bodies 181 VII. Of visible Figure and Extension 187 VIII. Some Queries concerning Visible Figure an- swered. 192 IX. Of the Geometry of Visibles 199 X. Of the Parallel Motion of the eyes 21 1 XI. Of our seeing objects Erect by inverted images. . 215 XII. The same subject continued 222 XIII. Of seeing objects Single with two eyes 238 XIV. Of the laws of vision in Brute animals 246 XV. Squinting considered hypothetically 249 XVI. Facts relating to Squinting 261 XVII. Of the effect of Custom in seeing objects Single. . 265 XVIII. Of Dr. Porterfield's account of single and double vision 272 XIX. Of Dr. Brigg's theory, and Sir Isaac Newton's conjecture on this subject 276 XX. Of Perception in general 287 XXI. Of the Process of Nature in perception 297 XXII. Of the Signs by which we learn to perceive Dis- tance from the eye. 303 XXIII. Of the Signs used in other acquired perceptions. . . 316 XXIV Of the Analogy between Perception, and the credit we give to Human Testimony 320 CHAPTER VII. CONCLUSION. Containing Reflections upon the opinions of Philosophers on this subject 338 INDEX 363 BIOGRAPHICAL SKETCH. DUGALD STEWART truly says, that the life of Thomas Reid "was uncommonly barren of those incidents which furnish materials for biography." His life was spent in comparative quiet and retirement, and was, therefore, not replete with varied incident. He was born April 26th, 1710, at Strachan, Kincardineshire, Scotland. His father was the Rev. Lewis Reid, a highly respected clergyman, who was descended from a succession of ministers of the Church of Scotland. His mother, Margaret Gregory, belonged to a family some- what distinguished in Scotland for their scientific attain- ments. Early in life Reid was sent to the parish school of Kincardine where he spent two years. From the parish school he went to Aberdeen, where he received instruction in the classics. When about twelve or thir- teen years of age he entered Marischal College. Here he was instructed in Philosophy by Dr. George Turnbull, who undoubtedly exerted a great influence upon his philo- sophical thinking.* He graduated from college in 1726. Receiving an appointment of librarian to the University, he continued his connection with it until 1736. During * Dr. McCosh says that Turnbull exercised a greater influence upon Reid's thinking " than all other masters and writers " com- bined. "The Scottish Philosophy," pp. 95-106. at TJ5IVBESIT7 2 BIOGRAPHICAL SKETCH. this period he devoted much of his time to the study of Mathematics. Resigning his office in 1736, he visited England in company with his friend, John Stewart, who afterward held the chair of Mathematics in Marischal College. They visited London, Oxford and Cambridge, where they were introduced to many noted literary men. In 1737, having been presented " to the living of New- Machar, " by King's College, Aberdeen, he entered upon his clerical work. The early part of his ministerial life in this parish was signalized by an intense hostility to him on the part of his parishioners. This was occasioned specially by the aversion which his people had to the law of patronage. Furthermore, he was accustomed, because of his modesty, to preach the sermons of Drs. Tillotson and Evans instead of his own. This practice was very offensive to the people. However, despite his unpopu- larity, through his fidelity to the interests of his parish, and his amiability of disposition, he soon ingratiated himself into the good will and affections of the people. In 1740, he was married to his cousin, Elizabeth Reid, daughter of Dr. George Reid, a London physician. His wife proved a great help to him in his work at New- Machar. While living here, "the greater part of his time," says Dugald Stewart, "was spent in the most intense study; more particularly in a careful examina- tion of the laws of external perception, and of the other principles which fornT^the^ groundwork of human knowledge."* In 1748, his first publication appeared. It was in the form of an Essay, published in the "Transactions" of the Royal Society of London, and "Collected Works," vol. x, p. 251. BIOGRAPHICAL SKETCH. 3 was entitled, "An Essay on Quantity, occasioned by reading a Treatise in which Simple and Compound Ratios are applied to Virtue and Merit. " The ' ' Trea- tise" to which Reid alludes was Hutcheson's " Inquiry into the Origin of our Ideas of Beauty and Virtue." In this "Treatise," Hutcheson made use of mathematical forms in illustrating moral subjects. Whether he meant to apply mathematical reasoning to such subjects may be doubted. Reid, however, was aware of the fact that Pitcairn and Cheyne had applied this form of reasoning to medicine, and he felt constrained to write an essay showing what rendered a subject capable of mathemati- cal treatment. In 1752, he was elected Professor of Philosophy, in King's College, Aberdeen. Shortly after his removal to Aberdeen, the ' ' Aberdeen Philosophical Society " was founded, principally through his endeavors. It included among its members such men as Campbell, Gerard, Beattie and John Gregory. * While connected with this society, he read papers which contained the essential principles of the "Inquiry." In 1764, he published the " Inquiry into the Human Mind on the Principles of Common Sense. " Reid's speculations on the subjects treated in the " Inquiry " were really begun in 1739, on the appearance of Hume's "Treatise of Human Nature." In the "Inquiry" Reid attempts to refute the scepti- cism of Hume by attacking the "theory of ideas" on which he thought this scepticism to be founded. Being thus directed against the sceptical philosophy of Hume, * Cf. McCosh, "The Scottish Philosophy," pp. 227-9, for an account of this society. 4 BIOGRAPHICAL SKETCH. he was desirous of subjecting his manuscript to Hume's perusal, so as not to misrepresent his philosophy in any particular. He was enabled to do this through the kind services of Dr. Blair, a mutual friend. After perusing it carefully, Hume wrote to Reid the following complimentary words: "By Dr. Blair's means I have been favored with the perusal of your performance, which I have read with great pleasure and attention. It is certainly very rare that a piece so deeply philo- sophical is wrote with so much spirit, and affords so much entertainment to the reader."* In 1763, Reid was called to the Professorship of Moral Philosophy, in the University of Glasgow, to succeed Adam Smith, who had resigned. He accepted the call, removing to Glasgow the following year. In the University he lectured on the intellectual and active powers of man, and on natu- ral jurisprudence and politics. Many of his colleagues were able men and they proved to be a great inspiration to him. During his connection with the University, he published "An Account of the Logic of Aristotle," as an appendix to Lord Kame's " Sketches of the History of Man." In 1781, he retired from the professorship, for the purpose of devoting his attention to the comple- tion of his philosophical works. In 1785, he published the ' ' Essays on the Intellectual Powers of Man, " a more elaborate treatment of the powers of the mind .than is contained in the "Inquiry." In 1788, he pub- lished the "Essays on the Active Powers of the Human Mind," advocating one form of Intuitional Ethics. This was the last work of his published during his lifetime. * Stewart's " Collected Works,'' vol. x., p. 256. BIOGRAPHICAL SKETCH. 5 Reid remained an active student almost till death. Among the most important efforts of the closing years of his life, were several papers written probably for a literary society in Glasgow. These were entitled, " Some Observations on the Modern System of Ma- terialism," and "A Free Discussion of the Doctrines of Materialism and Philosophical Necessity." One thing marred the serenity of these closing years. It was the death of his wife, with whom he had lived fifty-two years. Only one daughter, Mrs. Carmichael, of a large family of children, was still living. She was a great solace to him in his old age. On the yth of October, 1796, after a brief illness, he died. As a man, Reid was modest, sober, sincere, and de- vout. He was modest almost to diffidence. Indeed, Dugald Stewart expresses doubt as to whether Reid's modesty would have permitted him to publish the " Inquiry," had he not been encouraged to do so by his friends. His soberness and earnestness are manifest both in his life and writings. Something of his devout character may be learned from a confession and re-ded- ication of himself to the service of God, during his wife's illness, in the sixth year of their marriage. It is a most penitent and pathetic confession of dereliction of duty, and a most solemn pledge of a more devoted ser- vice to God.* As a philosophical thinker, Reid, if not profound, was, at least, deeply earnest and original. Cousin thought him to be a man of genius. He says: "Yes, Reid is a man of genius, and of a true and powerful * Cf. McCosh, " The Scottish Philosophy," pp. 199-200. 6 BIOGRAPHICAL SKETCH. originality; so we said in 1819, and so we say in 1857, after having held long converse with mighty systems, discovered their secret, and taken their measure."* McCosh says: " He has not the mathematical consecu- tiveness of Descartes, the speculative genius of Leibnitz, the sagacity of Locke, the spirituel of Berkeley, or the de- tective skill of Hume; but he has a quality quite as valua- ble as any of these, even in philosophy; he has in per- fection that common sense which he so commends, "f Sober earnestness and originality seem to be his merits as a philosophical thinker. His earnestness is manifest in his anxious endeavor to establish the reality of know- ledge, and thus to save philosophy from nihilistic scepticism. His originality is manifest in his breaking away from the " theory of ideas" which he had accepted on authority, and establishing philosophy upon a new basis. * Quoted by McCosh, " The Scottish Philosophy," p. 193. f Ibid., pp. 192-3. BIBLIOGRAPHY. /. On the Life of Reid. Dugald Stewart, "Account of the Life and Writings of Thomas Reid, D.D.," <' Collected Works," ed. by Hamilton, Edinburgh, 1854-60, vol. x, ch. v. Published also in "The Works of Thomas Reid, D.D.," ed. by Hamilton, Edinburgh, 1872, vol. i, pp. 1-35. Cf. Notes A, B, C, D, E, F, of Hamilton, appended to this account. James McCosh, "The Scottish Philosophy," New York, 1874, Art. xxvi. //. The Works of Reid. Complete Works in English: "The Works of Thomas Reid, D.D., now fully collected, with Selections from his Unpublished Letters. Preface, Notes, and Supplementary Dissertatipns, by Sir William Hamilton, Bart.," etc., 7th ed., Edinburgh, 1872, 2 vols. In French: " CEuvres Com- pletes de Thomas Reid, par M. Th. Jouffroy, avec des Fragments de M. Royer Collard," Paris, 1828-9, 6 tomes. For information concerning various editions of individ- ual works of Reid, cf. N. Porter, "Ueberweg's History of Philosophy," translated by Geo. S. Morris, New York, 1871-3, vol. ii, Appendix I, pp. 396-7. ///. Books of Reference. In English: J, Priestley, "Examination of Dr. Reid's Inquiry," etc., London, 1774. Dugald Stewart, "Collected Works," ed. by Hamilton, Edinburgh, 1854-60, vols. i, pp. 108-13; v, pp. 101-13. 7 8 BIBLIOGRAPHY. Th. Brown, '* Inquiry into the Relation of Cause and Effect," 3d ed., Edinburgh, 1818. "Lectures on the Phi- losophy of the Human Mind," Hallowell, 1829, especially lectures xxvi, xxvii. Sir Wm. Hamilton, "Lectures on Metaphysics," ed. by Mansel and Veitch, Edinburgh and London, 1870, vol. i, Appendix I (B), vol. ii, lectures xxi-xxiii. Also, "Preface, Notes and Supplementary Dissertations," in his edition of Reid's "Works," referred to above. J. F. Ferrier, " Reid and the Philosophy of Common Sense," " Blackwood's Magazine," 1847; the same in Lec- tures, ed. by Grant and Lushington, London, 1866, vol. ii, pp. 407-59- J. Walker, Notes in his abridged edition of Reid's " In- tellectual Powers of Man," Philadelphia, 1850. A. C. Fraser, "Essays in Philosophy," Edinburgh, 1856, Essays II and III. J. McCosh, "The Scottish Philosophy," New York, 1874, pp. 192-227, " Realistic Philosophy," New York, 1887, vol. ii, pp. 173-81. Thomas E. Webb, " The Veil of Isis," Dublin and Lon- don, 1885, pp. 123-62. A. Seth, " Scottish Philosophy," Edinburgh and London, 1885. Article on Reid, " Encyclopaedia Britannica," 9th ed., vol. xx. In French: Royer Collard, "Fragments de Royer Col- lard," Jouffroy's translation of Reid's Works. V. Cousin, " Philosophic Ecossaise," Paris, 1846, pp. 185-281. Thomas Jouffroy, Preface to his " (Euvres Completes de Thomas Reid," Paris, 1828-9. A. Garnier, "Critique de la Philosophic de Thomas Reid," Paris, 1840. J. P. A. Remusat, "Melanges," Paris, 1842. L. Peisse, Preface to " Fragments de Philosophic," 1840. In German : M. Kappes, " Der Common Sense bei Thomas Reid," Munich, 1890. E. Koenig, " Die Entvvickelung des Causalproblems von Cartesius bis Kant," Leipzig, 1888. BIBLIOGRAPHY. 9 IV. Consult also the following writers on the History of Philosophy: J. D. Morrel, " History of Modern Philos- ophy," 2d ed., London, 1847, vol. i, pp. 281-94. N. Porter, " Ueberweg's History of Philosophy," trans- lated by Geo. S. Morris, New York, 1871-3, vol. ii, Appen- dix I, pp. 394-403. F. D. Maurice, "Moral and Metaphysical Philosophy," London, 1873, vol. ii, pp. 580-6. G. H. Lewes, " Biographical History of Philosophy," New York, 1883, vol. ii, pp. 618-629. Falckenberg's " Geschichte der Neueren Philosophic," Leipzig, 1886, pp. 180-82. J. E. Erdmann, 'History of Philosophy," ed. by W. S. Hough, London and New York, 1890, pp. 271-4. RELATION OF REID'S PHILOSOPHY TO ITS PHILOSOPHICAL ANTECEDENTS. REID'S philosophy, like every other system of philos- ophy, cannot be thoroughly understood without taking into consideration its relation to preceding philosophic thought. It was one of twQjnovements in the world of philosophy awakengd by the scepticism of Hume the Philosophy of Common Sense, and the Critical Philos- ophy of Kant. Reid had been a disciple of Berkeley, virtually accepting the iSealismTof that acute thinker. But when he saw what he thought to be the logical out- come of Berkeley's philosophy, as manifested in the scepticism of Hume, he was somewhat alarmed, and be- gan to suspect the validity of ' ' the principles commonly received with regard to the human understanding."* After careful examination, he came to the conclusion that Hume's scepticism was the legitimate outcome of the "theory of ideas," i. e., the theory of perception, upon which it was founded. In his letter, dedicating the " Inquiry " to James, Earl of Findlaterand Seafield, he says: "For my own satisfaction, I entered into a serious examination of the principles upon which this Sceptical system is built; and was not a little surprised to Ifind that it leans with its whole weight upon a hypothesis Which is ancient indeed, and hath been very generally * "Works," vol. i, I. P., p. 283. 12 RELATION OF REID'S PHILOSOPHY received by philosophers, but of which I could find no solid proof. The hypothesis I mean is, that nothing is perceived but what is in the mind which perceives it. That we do not really perceive things that are external, but only certain images and pictures of them imprinted upon the mind, ^vEicITare csffistirimpremons and ideas. " * This theory he ascribed to all preceding philosophy both ancient and modern. In regard toHDescartes, Malebranche, Locke, Berkeley, and Hume, he says: "The system of all these authors is the same, and leads to scepticism. " ' ' Descartes no sooner began to dig in this mine, than scepticism was ready to brea^k in upon him. He did what he could to shut it out Malebranche and Locke, who dug deeper, found the difficulty of keeping out this enemy still to increase: but they labored honestly in the design. Then Berkeley, who carried on the work, despairing of securing all, bethought himself of an expedient: By giving up the material world, which he thought might be spared without loss, and even with advantage, he hoped, by an impregnable partition, to secure the world of spirits. But, alas ! the ' Treatise of Human Nature ' wantonly sapped the foundation of this partition, and drowned all in one universal deluge. " f It was the sceptical outcome of this "theory of ideas " which awakened Reid from his serene repose in authority, just as later it awakened Kant from his dogmatic slumber, and he resolved to make a new inquiry into "this sub- ject," independent of authority; for, said he: "I thought it unreasonable, upon the authority of philosophers, to admit a hypothesis which, in my opinion, overturns all * Works," Inq., p. 96. f Ibid., p. 103. TO ITS PHILOSOPHICAL ANTECEDENTS. 13 philosophy, all religion and virtue, and all common sense and, finding that all systems concerning the human understanding which I was acquainted with, were built upon this hypothesis, I resolved to inquire into this sub- ject anew, without regard to any hypothesis. " * Since, then, the special task of Reid was an examination of the ' ' theory of ideas, " it may be well for a thorough ap- preciation of his task, to briefly survey the development of modern philosophy from Descartes to Reid, with spe- cial reference to the " theory of ideas." The scepticism into which modern philosophy had issued, prior to Reid, seems to have been the result of its peculiar subjective tendency. This tendency char- acterized it from the beginning. Descartes' sceptical method forced him back upon the authorityoTconScious- ness. His^slaitmg^poinTln philosophy was universal doubt. f But this very fact of doubt led him to the rec- ognition of a fact that had to be accepted his own existence; Because, he reasoned, though I doubt every- thing, doubt, at least, remains. Doubt, however, is a form of thought. Hence the form ula? cogild^ ergo Now7~it is possible to think myself devoid of everything but thought; hence I must conclude that I am a being, the very essence of which is thought. Thus we arrive at a knowledge of mind. But what of our knowledge of an external world ? He inferred from the existence of clear and distinct ideas of things in the * Works," Inq., p. 96. f " First Meditation." J" Second Meditation." Ibid. 14 RELATION OF REID'S PHILOSOPHY r mind, the objective reality of things which occasioned them that these ideas were images or copies of things existing without the mind.* In short, his theory of perception is representative perception. However, this vicarious or representative character ~of ideas is only in- ferential with Descartes. He falls back upon the vera- city of God, (whose existence and veracity are known to us through our innate idea of God f ) for the trustworthiness of our knowledge of the external world. J We see, then, in both the sceptical method of Descartes, and also in his theory of representative perception the subjective tend- ency referred to above. Turning to Mai ebranche we find in his teaching, also, this subjective trend manifested. He says, material things are known to us only under the forms of ideas. As to the origin of these ideas, we are informed that they are not originated by the mind from itself because of its inability. || Neither are they given to us by things them- selves, fl How, then, do we come into possession of them ? Malebranche answers : through the mind's union with God, who possesses within Himself ideas repre- senting all things created by Him. God, by His pres- ence, is united to the finite mind He being the ' ' place of spirits " just as " space is the place of bodies." This union makes it possible for the mind to see in God that * " Sixth Meditation." f " Third and Fourth Meditations.' J "Sixth Meditation." " Dela Recherche de la Verite," Ivr. iii, pt. ii, ch. I. || Ibid., ch. 3. 11 Ibid., Ch. 2. TO ITS PHILOSOPHICAL ANTECEDENTS. 15 which represents things, viz., ideas.* It is thus that f ' we see all things in God." In the philosophy of Locke we find the same element of subjectivity. He wrote hisTamous ' l EsSayrnrHuman Understanding " with the purpose of explaining the or- igin, certainty and extent of knowledge. After explain- ing away all innate ideas, f~Xocke~ endeavored to show how we come into possession of ideas. He assumes that the mind in its original condition is like a blank sheet of paper, or a tabula rasa. J Whence, then, come its ideas ? The source of ideas is experience sensation and reflection. Having thus given the source of our ideas, he~clivides them into two kinds, simple and complex. A simple idea contains in it nothing but a uniform ap- pearance or conception in the mind, and is not distin- guishable into different ideas. These constitute the ma- terial of all knowledge. Complex ideas are formed by the mind by combining and uniting simple ideas. || Locke then proceeds to make another distinction be- tween our ideas, by pointing out the objective character of some, and the subjective character of others. He, of course, assumes the existence of an external world of corrjoreaTbodies. Now, that which in a body occasions an idea in the mind, he calls a quality. There are some qualities in bodies which cause ideas in the mind which are exact likenesses or resemblances of these qualities. Thejdea in the mind is a copy of the quali- ty in the body. These qualities are called primary * " De la Recherche de la Verite," Ivr. iii. pt. ii, ch. 3. f " Essay," bk. i, chs. 2, 3, 4- t " Essay," bk. ii, ch. I. Ibid., bk. ii., ch. i. H Ibid., ch. 2. 15 l6 RELATION OF REID'S PHILOSOPHY or original qualities of matter, viz., extension, solid- ity, figure, motion, number, etc. But there are other ideas in the mind which have no resemblance to the qualities in the bodies which cause them. To this class belong most of the ideas of sensation, viz., colors, sounds, tastes, smells, etc. These do not resemble their causes. The qualities which cause such ideas in us are the secondary qualities of bodies.* Locke then proceeds to the explanation of the idea of substance, and it is important to note his remarks on this point, because of the positions taken by Berkeley and Hume afterward. This idea, according to Locke, is not derived from sensation and reflection, as simple ideas are derived. Its origin is as follows: We frequent- ly recognize a certain combination of simple ideas, and we cannot conceive them as self-subsisting, so we are wont to provide a substratum for them as a ground of subsistence, and as a cause of their existence, which we call substance. However, although substance is an abstract idea, he believed in its objective reality, f After this consideration of the sources and kinds of ideas the mind has, we are prepared to hear Locke's conception of knowledge. Knowledge is simply "con- versant about our ideas." It is, "nothing but the perception of the connection and agreement or 'dis- agreement' and repugnancy of any of our ideas." Things are not known immediately by the mind, but through the intervention of ideas. How far, then, is knowledge real ? Only " so far as there is a conformity between our ideas and the reality of things." But what * " Essay," bk. ii, ch. 8. t. Ibid - bk - " ch - 2 3 TO ITS PHILOSOPHICAL ANTECEDENTS. 17 shall be our criterion in determining this conformity ? As Locke himself asks: * ' How shall the mind.when it perceives nothing but its own ideas, know, that they agree with things themselves ? " He answers this ques- tion by telling us that there are two kinds of ideas of which we may have assurance of their agreement with things. First, we have simple ideas, which are affections of the mind produced by external things, ' ' operating on the mind in a natural way." Hence these ideas cannot be fictions, but, being produced in this way, they "carry with them all the conformity which is intended or which our state requires." The second kind of ideas to which he refers in this connection, is complex ideas. These being formed by the mind itself, and not, with the exception of the ideas of substances, being intended to represent anything external, cannot mislead us.* We see, then, in what Locke says in regard to know- ledge, a recognition of its subjectivity. He admits that the mind does not have an immediate knowledge of things. It only knows them ' ' by the intervention of ideas. " He gives no other than a practical reason for the~correspondence of ideas and things. In this recogni- tion of the subjective character of our knowledge he cer- tainly anticipated Berkeley, as Reid suggests. He even anticipated Hume, and his taking refuge in a practical reason was doubtless more for the purpose of avoiding scepticism than idealism. Even for the assumption of the existence of an external world of corporeal substances, involved in his theory of perception, he really gives us no warrant of a speculative character. This, too, he ulti- * Essay," bk. iv, chs. i, 4. 1 8 RELATION OF REID'S PHILOSOPHY mately rests on practical grounds; apparently, also, for the purpose of escaping scepticism. It was this subjectivity of knowledge as involved in Locke's " theory of ideas," and the idealism and scepti- cism which were ultimately developed from it, which at- tracted Reid's attention, and impelled him to examine this theory, hoping to be instrumental in its overthrow, and to establish knowledge on a firm foundation. We must, then, trace this subjective tendency as manifested in the philosophy of Berkeley, and then in the scepti- cism of Hume, which awakened the reactionary philos- ophy of Reid. Berkeley's problem, as Prof. Fraser suggests, was an inquiry into the real meaning of substance and cause as external. In answering the first part of the question, the real meaning of material substance, he endeavored to show that the doctrine of substance as advocated by the philosophers, involved a contradiction. He claimed that the objects of knowledge are ideas, which ideas, of course, exist in the mind. Knowledge is concerned only with ideas. Now, when we ask what is meant by the existence of sensible things, it is evident ' ' that their esse is percipi. " All that really is meant by the exist- ence of a thing is that it is seen, touched, etc., in short, that it is perceived. To speak of something existing independent of a mind perceiving it is unintelligible and impossible. So-called things are objects perceived by sense, " and what do we perceive besides our own ideas or sensations ? and is it not plainly repugnant that any one of these, or any combination of them, should exist unperceived ? " The being of things, then, consists in their being perceived. Ideas cannot be images of sub- TO ITS PHILOSOPHICAL ANTECEDENTS. 19 stantial things, because an idea can only be like an idea, and things to be perceived must be ideas, and, if not, there is no sense in saying an idea is like something of which we can know nothing.* Berkeley then discusses the subject of primary and secondary qualities, in which discussion he apparently had Locke in mind. He objects to the distinction made by Locke, affirming our knowledge of primary qualities to be just as subjective as our knowledge of secondary qualities; extension, solidity, figure, etc., are ideas in the mind just as colors, odors, etc., are ideas; and, as ideas can only resemble ideas, and, as they exist only in the mind, extension, figure, etc. , cannot exist in an unthinking external substance. The very ' ' notion " of matter, then, involves a contradiction, f But if there be no external material substance if there be no world of corporeal substances how are we to account for the existence of our ideas ? They must have a cause. This brings us to the consideration of the second part of Berkeley's question, the nature of the originating cause. This cause, he says, cannot be an idea, for all ideas are "visibly inactive." "There is nothing of power or agency in them, " and hence an idea cannot be a cause. In the second place, the cause cannot be a material substance, for we have seen there is no such thing. What, then, is the cause ? The cause of the ideas must be an "incorporeal active substance or spirit." But it is not my spirit which originates them, because the ideas of sense are not originated by me * " Principles," 4, 6, 8, 10. f Ibid -> 1 5- 20 RELATION OF REID'S PHILOSOPHY. they are not produced by my will. The Will or Spirit which does originate them Berkeley infers to be God.* In our knowledge of spirit we seem to be conversant with something more than ideas. He tells us we have no idea of a spirit and can have none. However, he says, we have a " notion" of spirit. We have also a "notion" of other spirits and of relations. "We com- prehend our own existence by inward feeling or Reflection, and that of other spirits by Reason (inference). We may be said to have some knowledge or notion of our own minds, of spirits and active beings, whereof in a strict sense we have not ideas. In like manner we know and have a notion of relations between things or ideas, which relations are distinct from the ideas or things re- lated, inasmuch as the latter may be perceived by us without our perceiving the former, "f The preceding quotation is important as showing Berkeley's deviation from the position taken in the beginning of the ' ' Princi- ples," where he affirmed ideas to constitute the objects of our knowledge (see i). Here he recognizes another object of knowledge in ' ' notions. " Reid suggests that Berkeley took refuge in the ' ' notion " because of an aver- sion to scepticism. J Thus we see that Berkeley, beginning with Locke's doctrine of ideas as the only objects of knowledge, carried it so far as to reject his arbitrary assumption as to the objective character of certain ideas, existing as qualities of a substratum called substance, which substratum is also an unwarrantable assumption, thus * " Principles," 25, 26, 29. f Ibid., 89, cf. also 27. | "Works," Inq., p. 207. TO ITS PHILOSOPHICAL ANTECEDENTS. 21 resolving the world of material things into a world of ideas. In all of this the subjectivity heretofore referred to is still more manifest than in the preceding systems considered. In the philosophy of Hume, which we are now to consider, we shall see the culmination of this subjective tendency in scepticism. In the "Treatise on Human Nature" Hume argues as follows : " All perceptions of the human mind resolve them- selves into two distinct kinds, which I shall call impres- sions and ideas." By impressions, he means, "sen- sations, passions, and emotions." By ideas, he means, "the faint images of these in thinking and reasoning." Ideas, then, are images of impressions.* Every simple impression has its corresponding idea, and every simple idea has its corresponding impression, and he holds to the general proposition, ' ' That all our simple ideas, in their first appearance, are derivd from simple impressions, which are correspondent to them, and which they exactly represent, "f As to the 'division of impressions and ideas Hume said, that they could be divided into two classes simple and complex. Simple impressions and ideas admit of no distinction and are inseparable. Complex ideas are distinguishable into parts. Complex ideas include ideas of substances, modes and relations. "The idea of a substance as well as that of a mode, is nothing but a collection of simple ideas that are united by the imagi- nation, and have a particular name assigned them, by * Treatise on Human Nature," ed. by Green and Grose, Lon. don, 1886, vol. I, p. 311. | Ibid,, p. 314. 22 RELATION OF REID'S PHILOSOPHY which we are able to recall, either to ourselves or others, that collection."* Since we have no simple idea of sub- stance, derived from an impression of sense, Hume joined with Berkeley in refusing to affirm the objective existence of material substance. He then takes up the question of knowledge. Here he makes quite an effort to provide for that synthesis which knowledge implies. He finds this synthetic power in imagination, with its principles of association. In knowledge the imagination deals with seven different kinds of relations: "Resemblance, identity, relations of time and place, proportion in quantity or number, degrees in any quality, contrariety, and causation. " f These relations may be divided into two classes, the one depending upon the ideas compared : the other relations are "such as may be changed without any change in the ideas." Resemblance, contrariety, degree, proportion belong to the first class. They arise out of the very nature of the ideas, and certainty can only arise with these as objects of knowledge, but the knowledge is purely subjective. It can never transcend perceptions. Hume says that in the other class of relations it seems as though we are carried beyond our perceptions, but in this we are deceived. Neither identity, nor time, nor space carries us beyond perceptions.! But how is it with causation ? Here we seem to have assurance of conclusions which extend beyond the impressions of sense. Hence this relation must be carefully examined, and this examination on the part of Hume constitutes * "Treatise," pp. 312, 313, 321, 324. f Ibid., p. 372. J Ibid., pp. 375, sq. Ibid., pp-376-7- TO ITS PHILOSOPHICAL ANTECEDENTS. 23 the principal merit of his philosophy. When we believe in the existence of an object we have simply an idea of the object and no additional idea, and belief is distin- guished from incredulity simply in its superior liveliness and vigor. The vividness of an idea and belief are one and the same. Now, when an impression is vivid it gives its vividness to the ideas associated with it by resemblance, contiguity or causation.* Now, how are we to explain our belief in causation ? This idea we gain from ex- perience. Experience presents us with objects in con- stant conjunction, and thus produces in us "a habit of surveying them in that relation, that we cannot without a sensible violence survey them in any oth- er, "f But whence the belief of necessary connection implied in the relation of cause and effect ? This may be accounted for by a propensity, born of cus- tom, to pass from the impression or idea of an object to the idea of the object which usually attends it. " When any object is presented to it, it immediately conveys to the mind a lively idea of that object which is usually found to attend it, and this determination forms the ne- cessary connection of these objects. "J In brief, we mean by causation simply this : that when two objects have been constantly conjoined (in experience), the pres- ence of one determines the mind to form the idea of the other, and this determination is the result of habit or cus- tom. Hence this relation of cause and effect, which at first seemed to carry us beyond impressions, does not really do so, but resolves itself into a propensity, begotten of * "Treatise," pp. 394-400, sq. f Ibid., p. 424. t Ibid., pp. 450-68. 24 RELATION OF REID'S PHILOSOPHY custom, to pass from the impression or idea of an object to the idea of that object which usually attends it. The causal relation between things and ideas involved in the theory of Locke, Hume regarded as a mere assump- tion which experience did not justify. " The mind," he says, "has never anything present to it but the percep- tions, and cannot possibly reach the experience of their connection with objects. The supposition of such a connection is, therefore, without any foundation in rea- soning." The ultimate realities, then, with which the mind has to deal are individual, unreferable impressions, and from such impressions we cannot infer the existence of external material objects. Here we see idealism pure and simple. But he did not rest content with a denial of the reality of an external world; he also denied the reality of the soul. " Since all our perceptions are different from each other, and from everything else in the universe, they are also dis- tinct and separable, and may be considered as separately existent, and may exist separately, and have no need of anything else to support their existence." * Hence there is no necessity of a self as a substratum or subject of our perceptions. Proceeding upon his original thesis, that the perceptions of the mind are resolvable into impres- sions and ideas ideas being mere images of impressions he says : " If any impression gives rise to the idea of self, that impression must continue invariably the same, through the whole course of our lives ; since self is sup- posed to exist after that manner. But there is no impres- * "Treatise," p. 5r8. TO ITS PHILOSOPHICAL ANTECEDENTS. 25 sion constant and invariable. Pain and pleasure, grief and joy, passions and sensations succeed each other, and never all exist at the same time. It cannot, there- fore, be from any of these impressions, or from any other, that the idea of self is derived, and consequently there is no such idea" * Hume thinks we have no more an idea of a thinking substance as the support of per- ceptions than we have of an external substance as the support of qualities, and Berkeley in rejecting the one ought to have rejected the other, f To make his scepticism complete, Hume impeaches the veracity of reason : (i) Because it leads to con- clusions different from those of the senses ; (2) Because it is so frequently found to be fallible. (3) Because each judgment must be tested by other judgments "contain- ing uncertainty," and these in turn by other judgments containing uncertainty, and so Qnadmfinitum. Nihilistic scepticism is the fruit of Hume's endeavors. J Thus, in our brief historical survey of modern philos- ophy down- to Hume, we find it culminating in scepti- cism. The subjectivity which characterizes it from the beginning peculiarly paves the way toward the conclu- sion. It was against this scepticism thatReid recoiled. Repugnant as it was to him, and, as before stated, be- lieving it to be " inlaid " in all modern philosophy, and traceable to the theory of perception which he believed to be common to these systems, he determined to make a new inquiry into the subject, with the pur- * "Treatise," p. 533. f Ibid., pp. 517-18. "reatse, p. 533. f ., pp. 517-1. Ibid., p. 472, sg. " Works," Inq., pp. 96, 103, 106. 26 RELATION OF REID'S PHILOSOPHY pose of refuting this theory of perception, and plac- ing philosophy upon a new basis, by substituting a new theory of perception, and a new philosophical organon in the principle of common sense. In inquiring anew into this subject, Reid adopted a particular method. The " Inquiry" especially bears the marks of its age. Like other systems of philosophy, it is affected by the " Zeit-Geist." It is not often, if ever, that we have a purely closet philosophy a philosophy produced absolutely independent of the spirit of the age. Consciously or unconsciously speculation is af- fected by the subtle influences of the intellectual and moral atmosphere in which it is brought forth. This influence of the spirit of the age upon Reid's philosophy may be seen in the method which he adopts the exper- imental or inductive method. The results of an appli- cation of this method in the study of physical phenom- ena, by such men as Newton, were wonderful. Reid, who was an earnest student of physics, was greatly im- pressed by the validity and fruitfulness of this method, and he came to the conclusion that it was the only method which should be employed in the investigation of the phenomena of the mind, and determined to apply it. All through the "Inquiry" the steadfastness of his purpose is manifest. Dugald Stewart truly remarks, that "the influence of the general view opened in the ' Novum Organon' may be traced in almost every page of his writings: and, indeed, the circumstance by which these are so strongly and characteristically distinguished, is that they exhibit the first systematical attempt to ex- emplify in the study of human nature the same plan of TO ITS PHILOSOPHICAL ANTECEDENTS. 27 investigation which conducted Newton to the properties of light and to the law of gravitation. " * Having thus stated the aim and method of Reid's philosophy, let us proceed to an exposition of the same. And, first, let us consider the theory of perception, which he urged in opposition to the " theory of ideas." His theory of perception has both negative and positive aspects. In its negative aspect, it is a denial of (i) the particular form of perception which Reid ascribed to all preceding philosophy. This particular form Reid conceived to be, as Hamilton suggests, that the object before the mind in perception is ' ' always a tertium guid I numerically different both from the object existing and " | from the subject knowing. " f This is the theory which Reid felt called upon to den^ the calling into question of which he deemed to be the special merit of his own philosophy.J (2) In its negative aspect, Reid's theory of perception is a denial that we attain our knowledge of external objects by an act of reasoning. In denying the theory of ideas his argument runs as follows: i. The theory is in direct opposition to the universal sense of men uninstructed in philosophy. When a plain man sees the sun and moon he does not doubt that there are objects far distant from himself, and not merely ideas in his mind. If he asks whether there are no substantial beings called sun and moon, the answer which he will * "Collected Works," vol. x, p. 259. t Works, Inq., Note, p. 106. J Ibid., p. 88. Cf. " Works," Inq., pp. 201-1 1 and especially I. P., pp. 298-309. 28 RELATION OF REID'S PHILOSOPHY get from the philosophers will differ. Locke and his ^""7 predecessors will answer, that there are such beings, but they never appear to us in person, but only b^_ideas which are their representatives in our minds, and all we know of them must be gained from these ideas. Berke- ley and Hume would say, that there are no such sub- stantial beings. That is simply a prejudice of the vulgar. Berkeley would say that nothing exists but ideas and minds, and these things are simply ideas in our minds. Hume would say, only ideas exist, and the mind is simply a series of ideas bound together by a few relations! To the plain man tKis must, of course, be op- posed to "the dictates of common understanding." 2. Those who advocate the "theory of ideas" have, as a rule, assumed the existence of the ideas, and have regarded their existence as unquestionable. The few arguments which they have incidentally offered in their behalf have been " too weak to support the conclusion." Locke, for example, says we are conscious of such ideas. But, says Reid, we are not conscious of them. All we are conscious of, are the operations of the mind, such as perceiving, remembering, etc., and not of the objects of such operations. And thus he quotes others, endeavoring to show the assumptive character of their positions, and the weakness of their "incidental arguments." 3. Although there is a unanimous agreement among philosophers on the subject of the existence of ideas, there seems to be a pronounced disagreement among them with respect to everything else concerning the ideas. This ought not to be, if they are a reality, for of all things they ought to be most easily accessible to knowledge. Some hold that they are self-existent; others, that they TO ITS PHILOSOPHICAL ANTECEDENTS. IQ exist in the Divine mind. Some hold that they exist in our minds; others, that they exist in the brain or sensorium. Some hold that they are innate, or, at least, a part of them; others, that they are all adventitious. Some, that they are gained through the senses; others, that they are derived from sensation and reflection. As to how they arise, some think the mind originates them; others, that they are occasioned by external causes: still others, that they are produced by God acting upon the mind. And so on, in regard to other features of the ideas there is this wide disagreement. This, as has been suggested, ought not to be, if ideas really exist, for they ought to be very accessible to knowledge. 4. Ideas do not improve our knowledge of the various operations of the mind. They .were, doubtless, brought forward for this purpose. ' ' This power of perceiving ideas is just as inexplicable as any of the powers explained by it." 5. The consequences of this theory are such as to pre- judice every man against it who has a due regard for the common sense of mankind. Aside from the peculiarities and absurdities which flow from the theory as seen in ancient philosophy, we see in modern philosophy con- sequences which are enough to prejudice mankind against it. It has led to the attempts of trying to prove the existence of material things. And who does not see that philosophy must make a very ridiculous figure in the eyes of sensible men while it is employed in muster- ing up metaphysical arguments to prove that there is a sun and a moon, an earth and a sea ? It has led to such paradoxes as, "that the secondary qualities of body are not qualities of body at all, but sensations of the $O RELATION OF REID*S PHILOSOPHY mind: That the primary qualities of body are resem- blances of our sensations: That we have no notion of duration, but from the succession of ideas in our minds: That personal identity consists in consciousness; so that the same individual thinking being may make two or three different persons, and several different thinking be- ings make one person: That judgment is nothing but a perception of the agreement or disagreement of our ideas." But these consequences are tolerable when brought into comparison with those which we find in Berkeley and Hume. Here we have the negation of the world of mat- ter and the world of mind, and nothing is left us but ideas. A general scepticism is the result. These are the "noble fruits" which this "theory of ideas " has brought forth. Such consequences, so startling to common sense, must cause a reaction against the theory. In the second place, Reid denies that we attain to a knowledge of external objects by an act of reasoning. He depends mainly upon the strength of his own theory of perception for an overthrowal of this doctrine. Having thus considered the negative aspects of Reid's theory of perception let us proceed to a consideration of its positive aspects. The following are the main features of his theory: I. Sensation. 1. A sensation is a simple, inexplicable affection of the mind. "It appears to be a simple and original af- fection or feeling of the mind, altogether inexplicable and unaccountable." * 2. Sensations exist onlyji^ f ^ p miqrl They do not Works," Inq., p. 105. TO ITS PHILOSOPHICAL ANTECEDENTS. 31 exist in material things not even in our own bodies. "The sensations of touch, of seeing, and hearing, are all in the mind, and can have no existence but when they are perceived." * 3. Sensations are antecedent to perceptions. The "sensation is followed by the perception of the ob- ject."t // Perception. i. Perception defined. Sensation naturally suggests a ' ' notion " or u conception " of, together with a be- lief in the existence of. an object This is perception. ' ' But I think it appears, from what hath been said, that there are natural suggestions: particularly that sensation suggests the notion of present existence and the belief that what we perceive or feel does now exist, . . . and that our sensations and thoughts do also suggest the notion of a mind, and the belief of its existence, and of its relation to our thoughts. . . . And in like manner . . . certain sensations of touch, by the constitution of our nature, suggest to us extension, solidity and mo- tion, "f In the "Intellectual Powers," we find Reid essentially agreeing with his definition of perception given in the "Inquiry." He says: "If, therefore, we attend to that act of our mind which we call the perception of an external object of -sense, we shall find in it these three things: First, Some conception or notion of the object perceived ; Secondly, a strong and irresistible conviction and a belief of its present existence; and * "Works," Inq., pp. 159, 105, 187; I. P., pp. 229, 310. f Ibid., pp. 186, 187; I. P., p. 320. J Ibid., Inq., p. in. 32 RELATION OF REID'S PHILOSOPHY Thirdly, that this conviction and belief are immediate, and not the effect of reasoning." In other words: Sensations are attended by certain original "sugges- tions " and beliefs, and this constitutes perception. 2. Perception illustrated. This theory of perception will be more intelligible to us if we examine Reid's doctrine of "suggestion " as we find it illustrated in his treatment of the so-called secondary and primary quali- ties of body. Reid agreed with Locke in regard to the essential distinction between the secondary and primary qualities, which Berkeley and Hume had endeavored to remove.* ~The two points of distinction to which he directs attention, are: (i) The ease with which we distinguish between the sensation and its external corre- late in the case of secondary qualities as compared with primary qualities. (2) The sensations in the case of secondary qualities only suggest a power or quality of the object as a cause; whereas, in the case of the pri- mary qualities, the sensation also suggests the nature of the cause. Now, in the treatment of the secondary and primary qualities, as above stated, we may see Reid's theory of perception, as sensation attended by original suggestions and beliefs, fully illustrated. (a. ) In the case of secondary qualities, take, for ex- ample, the secondary quality smell. On this point Reid makes the following remarks: "The smell of a rose signifies two things: First, a sensation, which can have no existence but when it is perceived, and can only be in a sentient being or mind. Secondly, it signifies some power, quality, or virtue, in the rose, or in efflu- * "Works," Inq., p. 123; I. P., p. 314. TO ITS PHILOSOPHICAL ANTECEDENTS. 33 via proceeding from it, which hath a permanent exist- ence, independent of the mind, and which, by the con- stitution of nature, produces the sensation in us. By the original constitution of our nature we are both led to believe that there is a permanent cause of the sensation, and prompted to seek after it: and experience determines us to place it in the rose." * That is, sensations of smell and, as he elsewhere suggests, those of taste, sound, etc., suggest to us qualities in objects as the causes of these sensations. Thus sensations attended by suggestions are perception so far as the secondary qualities are con- cerned. As Hamilton interprets Reid on this point: "In a sensation (proper) of the secondary qualities, as affections in us, we have a perception (proper) of them as properties in objects and causes of the affections in us. " f (b. ) In the case of primary qualities his theory of per- ception as sensations attended by original " suggestions" and beliefs is still more marked. Take, for example, the sense of touch. Here we are liable to confound the sensation and the quality of body from which it arises. The sensation is only a "sign "of a quality in the ex- ternal body: but we are wont to pass quickly from the " sign" to the thing signified without making a distinc- tion. There is, nevertheless, a distinction. The sensa- tion has no similitude to the quality known as hardness in the external object. How, then, do we come to have the "conception" and "belief" (perception) of the ob- jective reality of what we call hardness in body ? For cer- tainly we have such a perception. This " conception * "Works," Inq., p. 114. f Ibid., Note D, p. 884. 34 RELATION OF REID'S PHILOSOPHY and belief," Reid answers, comes to us in the following manner: "By an original principle of our constitution a certain sensation of touch both suggests to the mind the conception of hardness, and creates the belief of it: or, in other words, that this sensation is a natural sign of hardness. "* Now what is true of hardness is also true of softness, roughness, smoothness, figure and motion. "All these," says Reid, "by means of corresponding sensations of touch, are presented to the mind as real external qualities; the conception and belief of them are invariably connected with the corresponding sensa- tions, by an original principle of human nature, "f The same thing is true in regard to extension and figure. ' Our perception of extension and figure is a natural sug- gestion attending sensations of touch. "Extension, therefore, seems to be a quality suggested to us, by the very same sensations which suggest the other quali- ties above mentioned (i. e., other primary qualities). When I grasp a ball in my hand, I perceive it at once hard, figured and extended. The feeling is very simple, and hath not the resemblance to any quality of body. Yet it suggests to us three primary qualities perfectly distinct from one another, as well as from the sensation which indicates them. When I move my hand along the table, the feeling is so simple that I find it difficult to distinguish it into things of different natures: yet, it immediately suggests hardness, smoothness, extension and motion things of very different natures, and all of them as distinctly understood as the feeling which sug- * " Works," Inq., p. 121. f Ibid., Inq v p. 123. TO ITS PHILOSOPHICAL ANTECEDENTS. 35 gests them. " * It is apparent from the above quotations concerning both the secondary and primary qualities that what Reid means by perception is sensations at- tended by original "suggestions "in the form of "no- tions" or " conceptions " and beliefs. When he uses the terms "sign ' and "signify," he means simply that the sensation is a "sign " of a quality in the external thing ; and what he means by this, is that the sensation suggests a " notion" or " conception" of, and belief in the existence of, that quality. The "notion " and "conception" are ' ' suggestions " attending sensations, immediately inspired by the constitution of our nature. The " belief" in the existence of the quality or object attending sensations is also immediately inspired by our constitution. Percep- tion, then, according to Reid, is, as was suggested in the beginning, sensations attended by certain original , suggestions and beliefs. Or, to put the definition more nearly in his own language: perception is the " notion " or "conception" of an object, together with a belief in its existence; which " notion " and belief are originally "suggested" or "inspired" by the constitution of our nature, on the occasion of a sensation arising in the mind. The foregoing is the substance of Reid's theory of per- ception as we find it developed in both the " Inquiry" and the ' ' Intellectual Powers. " Two questions very nat- urally suggest themselves here: i. Was Reid right in attributing the "theory of ideas " to preceding philoso- phy? In regard to this question there is a differ- ence of opinion. Such critics of Reid as Priestley, f "Works," Inq., pp. 124-5. f " Remarks on Reid, Beattie, and Oswald," 2d ed., 3, p. 30. 36 RELATION OF REID'S PHILOSOPHY Brown,* and Webb f think that Reid seriously erred in his interpretation of the large majority of previ- ous systems of philosophy. On the other hand, Hamilton J comes to Reid's defense, and, while admit- ting him to be mistaken in several instances, regards him, especially in respect to modern philosophy, to have good grounds for ascribing this theory to his predecessors. To discuss this question would require a survey of the entire history of philosophy, which, of course, cannot be done here. If, however, the reader desires to determine the correctness of Reid's interpretation, I will be pardoned in once more call- ing attention to the fact that Reid's conception of the "theory of ideas "was not what is ordinarily under- stood by representative perception. The theory which he ascribes to his predecessors is, that in perception there is an image or " idea " existing between the mind perceiving and the existing object numerically different from both. 2. From all that is said upon the sub- ject, what are we to understand Reid's theory of per- ception really to be ? Is it the theory of immediate or intui- tive perception a. direct gaze upon extra-mental, substan- tial objects; or, is it some form of representative percep- tion, only one form of which, viz., the tertium quid form, it is claimed by some, he really combated ? Concerning this question, it must be admitted that it is an exceed- ingly difficult task to determine precisely what Reid's theory of perception is. This difficulty is the result not only of the looseness of his presentation of the subject, * " Philosophy of the Human Mind," lees, xxvi, xxvii. f " The Veil of Isis," pp. 125-162. \ "Metaphysics," lees, xxi, xxii. TO ITS PHILOSOPHICAL ANTECEDENTS. 37 but also of his failure to fully think the subject through. By some, and doubtless by the majority of scholars who have given Reid's philosophy thoughtful consideration,, he is supposed to advocate the theory of immediate per- ception. So emphatically do they affirm this to be his theory, that they regard it, in connection with his doc- trine of common sense, to determine his historical posi- tion or significance. By others, and for very good rea- sons, he is supposed to teach some form of representative perception. This form, to use the terminology of Ham- ilton, may be called egoistical representationism, i. e., the object before the mind in perception is a subjective representative object, which subjective object is a modi- fication of the mind. And, as there are two forms of egoistical representationism, the form which is ascribed to Reid is: that the subjective object is really identical with the perceptive act, but logically distinguished from if, "being simply the perceptive act itself, considered in one of its relations, to wit, to the immediate object, the reality rep- resented, and which, in and through that representation alone, is objectified to consciousness and perceived."* As has been suggested, those who ascribe some form of representative perception to Reid, have good grounds for doing so. His use of "notion," "conception," "suggestion," etc., certainly is favorable to an interpre- tation of his teachings in favor of some form of mediate, rather than immediate, perception. On the other hand, there are good reasons for believing that he meant to teach the doctrine of immediate or intuitive perception. Sir Wm. Hamilton has, with characteristic thoroughness, careful - " Works," Note C, p. 818. 38 RELATION OF REID'S PHILOSOPHY ly selected and arranged the evidence to be found in both the "Inquiry" and the "Intellectual Powers" bearing on each view of Reid's theory of perception. An examination of this evidence will put us in a better posi- tion to come to some conclusion on this disputed point* Following the order of Hamilton, the following is the substance of the leading arguments in favor of egoistical representationism in the form stated above, f I, Reid's doctrine of primary qualities implies it. He teaches that the primary qualities of body are sug- gested through certain sensations. They are suggestions, or conceptions, immediately arising in the mind, we know not how by a natural magic as it were on oc- casion of certain sensations. If the primary qualities are nothing more than suggestions, or conceptions "inspired by a means unknown, " then they are only representations of it knows not what, blindly determined by the mind. Per- ception is simply the consciousness of these concep- tions or suggestions, hence our knowledge of the exter- nal world would certainly not be immediate. The im- mediate object before the mind would be a conception or suggestion and not an extra-mental object. Hence Reid must be considered an advocate of representative perception. (Inq., pp. 122, 123, 128, 183, 188 ; I. P., pp. 258, 318, 320.) This argument, somewhat over- drawn by Hamilton, seems to me to be one of the strongest arguments in favor of Reid's theory being that of egoistical representationism: because in his teach- ing, concerning the primary qualities, the mind has naught but sensations accompanied by "suggestions" * " Works," Note C, pp. 819-24. f Ibid -i Note c P- 820-2. TO ITS PHILOSOPHICAL ANTECEDENTS. 39 or " conceptions" to deal with. Hamilton, who be- lieves Reid to hold the theory of immediate perception, makes a plea for his view in regard to this point by say- ing, we must not hold Reid too rigidly to what he says in the "Inquiry" on the subject of ''suggestion," as he does not mention it in the "Intellectual Powers," which would seem that he was doubtful of its tendency. But this plea, to my mind, has little force, because, in the first place, Reid did not retract the doctrine of "sug- gestion "in the "Intellectual Powers ; " and, in the second place, although he does not use the word "suggestion" in the " Intellectual Powers," his theory of perception in both the "Inquiry" and "Intellectual Powers" is essentially the same. 2. Intuitive perception implies that a knowledge and belief of the existence of an external world is given in perception, and there is no need of resorting to " natural magic," "inspiration," etc., to explain that knowledge and belief, as Reid really does. In the case of cos- mothetic idealism, whose theory of perception is repre- sentative perception, in which " the mind is determined to represent to itself the external world, which, ex hypo- thesi, it does not know, the fact of such representation can only be conceived possible through some hyper- physical agency." Now, the rationale of Reid's theory of perception "natural magic," "inspiration," "in- fused faith," etc., rather makes a representationist than a presentationist out of him. (Inq., 122, 188; I. P., 257.) There is certainly some force in the above argument, and in the "Intellectual Powers," Reid, in a measure, approaches the Cartesian doctrine of a Deus ex machina 40 RELATION OF REID'S PHILOSOPHY in his remarks on perception. (Seel. P., p. 257.) Even Hamilton admits this. (See note, p. 257, of Reid's "Works," also Note C, p. 821.) 3. Reid equalizes perception and imagination. He speaks of imagination as a faculty of immediate know- ledge. Now all will admit that in an act of the imagina- tion the external object is known only mediately, in a representative way. Hence Reid must have meant by ascribing to the faculty of imagination immediate know- ledge, that its knowledge is not representative in the tertium quid sense, as advocated by the "theory of ideas," but that it is really mediate in the sense in which we ordinarily speak of the images of the imagination be- ing representative. If this be so, in the case of the im- agination, then when Reid equalizes perception and imagination by attributing to both of them immediate knowledge, he must use the word immediate in the case of perception, just as he uses it in the case of imagination, viz., immediate in opposition to mediate as advocated by the tertium quid theory, but nevertheless mediate in the true sense. Or, as Hamilton states the argument: " In calling imagination of the past, the distant, etc., an immediate knowledge, Reid, it may be said, could only mean by immediate, a knowledge effected not through the supposed intermediation of a vicarious object, nu- merically different from the object existing and the mind knowing, but through a representation of the past, or real, object in and by the mind itself ; in other words, that by mediate knowledge he denoted a non-egoistical, by immediate knowledge an egoistical, representation. This being established, it may be further argued that in calling perception an immediate knowledge, he, on the tO ITS PHILOSOPHICAL ANTECEDENTS. 41 same analogy, must be supposed to deny, in reference to this faculty, only the doctrine of non-egoistical represen- tation. This is confirmed by his not taking the distinc- tion between perception as a presentative, and memory, for instance (i. e., recollective imagination), as a repre- sentative cognition : which he ought to have done, had he contemplated, in the former, more than a faculty, through which the ego represents to itself the non-ego, of which it has no consciousness no true objective and immediate apprehension." * (Inq., p. 106; I. P., pp. 226, 233, 292, 293, etc.) Hamilton tries to lessen the force of this argument by saying that it merely ' ' proves that Reid's perception may be representative, not that it actually is so."f How- ever, when taken in connection with the preceding argu- ments, it at least shows that the logical implication of Reid's presentation of his theory of perception is repre- sentationism. 4. Reid, in some instances, seems to make perception the result of inference, so that the remote cause is the object perceived, and, hence, not the immediate object of perception. Hence perception cannot be immediate. (Inq., p. 125; I. P., 259, 260, 309, 326, 328.) This argument has weight. Reid seems to teach that perception is the result of inference, thus making it mediate instead of immediate. However, it must be taken into consideration, that there are other passages in which he expressly denies that perception is the result of inference. (I. P., 259, 260, 309, 326, 328.) There are several minor arguments favoring this inter- * " Works," Note C, pp. 821-822. f Ibid., p. 822. 42 RELATION OF REID*S PHILOSOPHY pretation of Reid, but they are hardly of sufficient im- portance to be noticed here.* On the other hand, let us state the evidence favoring the interpretation of Reid's theory of perception as immediate perception, f 1. " Knowledge and existence only infer each other when a reality is known itself or as existing." That is, knowledge and existence are only convertible when there is a knowledge of reality in itself. It is only under such conditions that we can say that the reality "is known because it exists, and exists since it is known. " This is what constitutes an immediate perception. Now Reid's teaching is in harmony with the above position. He says: "It seems admitted as a first principle, by the learned and unlearned, that what is really perceived must exist, and that to perceive what does not really exist is impossible. " (I. P., p. 274.) 2. All philosophers agree that the idea or representa- tive object is immediately apprehended, and that as thus apprehended it exists ne.cessarily. Now if Reid affirms that external objects are perceived not less immediately he must be regarded as holding the theory of immediate perception. This he affirms. (I. P., 263, 272, 274, 289, 446.) 3. All admit that mankind at large believe that the external reality is the immediate object of perception. Mankind, in general, take the "common- sense" view of the world i. e., they believe in the existence of a world of substantial "things," which " things " are immediate- ly perceived. Only philosophers affirm the contrary. Reid's " Works," Note C, pp. 821-2. f Ibid., pp. 822-3. TO ITS PHILOSOPHICAL ANTECEDENTS. 43 Now Reid affirms himself to be on the side of mankind in general or, as he suggests, on the side of the vulgar, in this respect. (I. P., 275, 284, 298, 299, 302.) This argument certainly has great force. Reid refers frequently to the view of the " vulgar," which is the be- lief that in perception we gaze immediately upon an ex- ternal world of " things," and then places himself on the side of the " vulgar." (See above references.) 4. Reid affirms, that in self-consciousness we have an immediate knowledge of the modifications of self: and adds, that in perception we have knowledge just as immediate of the qualities of the "not-self." (I. P., 263, 269, 373.) Thus runs the evidence in favor of both interpreta- tions. It is apparent at once that there are good grounds for holding either view. Sir Wm. Hamilton and most interpreters, for the reasons above mentioned, think that Reid really held the theory of immediate per- ception. Brown, Webb, and Ferrier think his theory was a theory of representative perception egoistical representationism. When the doctors disagree, who shall decide ? It is quite evident, from a consideration of the above evidence, that it is not well to dogmatically affirm either view. My own opinion is, that Reid meant to teach natural realism, with its theory of immediate perception; but his presentation of the subject is so loose, owing to a looseness of language and a failure to fully think the subject through, as to afford good grounds for supposing him to teach cosmothetic ideal- ism, with its theory of egoistical representationism. This is the only way that Reid can be saved from self- contradiction. 44 RELATION OF REID'S PHILOSOPHY Let us now proceed to the second feature of Reid's philosophy his doctrine of common sense. Not only did Reid oppose to scepticism his theory of immediate perception, to subvert the ' ' theory of ideas, " on which he supposed this scepticism to be based; but he also es- tablished his organon of common sense as authority for the acceptance of certain fundamental principles which this scepticism denied. Reid used this term in a rather am- biguous way, and often in such a way as to mislead the reader as to his real meaning. Especially careless is he in the use of the term in the "Inquiry,"* where he lays himself open to an interpretation which is really opposed to his real meaning particularly as indicated in the " Intellectual Powers. " f Reid is sometimes supposed to mean by common sense, the undeveloped belief of the masses, which he would oppose to the reasonings of philosophers. Again, he is supposed to mean by the term "good sense," sound understanding. Even Kant was misled in thus interpreting Reid. J Sometimes he is thought to mean the voice of the majority, or uni- versal assent. But, while his carelessness lays some of his remarks open to such interpretations, a critical study of his works reveals the fact, that what he really means by the principles of common sense is, the self-evident prin- ciples of reason; ws\& what he means by common sense is' the faculty of such principles ; or, reason judging self-ev- ident truth. This is quite evident from the following statements, taken both from the "Inquiry" and the "Intellectual Powers": * P- 101. f p. 425. f " Prolegomena," pp. 4-6. TO ITS PHILOSOPHICAL ANTECEDENTS. 45 "If there be certain principles, as I think there are, which the constitution of our nature leads us to believe, and which we are under a necessity to take for granted in the common concerns of life, without being able to give a reason for them; these are what we call the principles of common sense ; and what is manifestly con- trary to them is what we call absurd. " * " It is absurd to conceive that there can be any opposition between reason and common sense. It is indeed the firstborn of reason: and, as they are commonly joined together in speech and in writing, they are inseparable in their nature We ascribe to reason two offices, or two degrees. The first is to judge of things self-evident; the second to draw con- clusions that are not self-evident from those that are. The first of these is the province, and the sole province, of common sense: and, therefore, it coincides with reason in its whole extent, and is only another name for one branch or one degree of reason, "f The self-evident principles of reason, then, are what Reid means by com- mon-sense principles; and by common sense he means reason declaring self-evident truth. It will appear, also, from the above citations, that the criteria of common- sense principles, with Reid, are, necessity and self-evi- dence. Reid, however, was very unfortunate in his classification of these principles. He places on the list of common- sense principles, truths which are nothing more than mere generalizations of experience. His loose classifica- tion has had considerable to do in bringing condemnation upon his philosophy. J * "Works," Inq,, p. 108. f "Ibid., I. P., p. 425. J Ibid., I. P., pp. 434-468. 46 RELATION OF REID'S PHILOSOPHY. The historical significance of Reid's philosophy, then, lies in calling into question the " theory of ideas" on which the scepticism of Hume is founded, and in op- posing to it the theory of immediate perception, and the organon of common sense. * Works," I. P., pp. 441-461. THE INFLUENCE OF REID'S PHILOSO- PHY UPON SUBSEQUENT PHILO- SOPHIC THOUGHT. CONTEMPORANEOUS with Reid, and influenced by him, were James Oswald * and James Beattie,f also exponents of the doctrine of common sense. Both adhered more slavishly to the doctrine than Reid. Oswald, in his "Appeal," virtually uses the same argument which is used by Reid, so far as the validity of so-called funda- mental truths is concerned. Common sense discerns and vouches for all fundamental truths. It is reason de- claring self-evident truth. Now just as common sense declares self-evident truth in other departments of thought, so it declares primary truths in the domain of morals and religion. In endeavoring to strengthen the argument from common sense he makes use of the reductio ad absurdum. Beattie's ' ' Essay " was called forth specially by the scepticism of Hume. In it, with Reid, he opposes the affirmations of common sense to scepticism. He holds to the validity of so-called primary truths. Our ground for accepting them is their * " An Appeal to Common Sense in behalf of Religion," London, 1766-72. f " Essay on the Nature and Immutability of Truth in Opposition to Sophistry and Scepticism," 4th ed., London, 1773. 48 THE INFLUENCE OF REID'S PHILOSOPHY own self-evidence. So that his doctrine is essentially the same as Reid's. The real successorof Reid was Dugald Stewart.* He, too, is in substantial harmony with the views of Reid. 1. He agrees with him in regard to the method which ought to be adopted in studying the phenomena of the human mind the inductive method, f 2. In his theory of perception he is in substantial agreement with Reid. He regards perception as the "notion " of an object, which notion and belief are in- stinctively suggested or inspired on the occasion of sen- sation. J Like Reid, he doubtless meant to teach imme- diate perception, but, unfortunately, did not succeed much better than Reid in clearing his doctrine of those inconsistencies and ambiguities which render the theory capable of a two-fold interpretation. That is, although he doubtless meant to teach the theory of immediate perception common to natural realism, his presenta- tion of the subject involves egoistical representationism. 3. With respect to his doctrine of commojL-Sfinse, we find him also in substantial agreement with Reid. However, Stewart did not like the term " the principles of common sense," thinking it open to serious objections, because of its associations and ambiguity. For this term he substituted the expression: " the fundamental laws of human belief." These laws he considered "the constituent elements of reason." This doctrine he emphasized just as much as Reid did, and he saw in it * " Collected Works," ed. by Hamilton, Edinburgh, 1854-60. f Ibid., vol. ii, Int., i and 2. J Ibid., vol. ii, ch. i. UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 49 the only true organon for philosophy, and the antidote for scepticism. * Dr. Thomas Brown, f was also, to a certain extent, a disciple of Reid. Influenced, however, by the teach- ings of Hartley, and the sensationalism of the French Ideologists, he, in a measure, deviated from some of the positions of the Scottish School. This is especially manifest in his analysis and classification of the pheno- mena of the mind. Reid and Stewart being emphati- cally opposed to sensationalism, did not carry their psy- chological analysis as far as they doubtless would have done, had not sensationalism been such a bugbear to them. Brown, however, was not to be so easily fright- ened, and he carried his analysis to a greater simplifica- tion. He tried to unite some of the positions of the Sensational School with certain positions of the Scot- tish School. 1. His method was that of the Scottish School, viz., the inductive method. He insisted upon, applying the method adopted by physical science. J 2. The result of an application of this method was a reduction of the number of original faculties to which Reid and Stewart held, and the resolving of all mental phenomena into modifications of the mind itself. 3. His theory of perception differs from the theory of Reid and Stewart. It is egoistical representationism, i. e., * "Collected Works," vol. iii, ch. i. f "Lectures on the Philosophy of the Human Mind," Hallowell, 1829. J Ibid., lees, ix, x, xi. Ibid., lees, xvi, xvii. 50 THE INFLUENCE OF REID'S PHILOSOPHY the object before the mind in perception is not an extra- mental, material object, but a mental object, which ob- ject is merely a modification of the mind itself."* 4. On what authority, then, do we believe in an ex- ternal world? Brown answers: through the intuitive principle of causation, we are led to infer the existence of an external world. On occasion of certain sensations arising in the mind, we infer an extra-mental reality as their cause, which external cause he affirmed to be an extended, material object f Brown, then, retreats from natural realism with its doctrine of immediate perception, and goes over to cosmothetic idealism, with its doctrine of mediate perception affirming, however, the existence of an external, material world on the strength of the causal principle. In Sir William Hamilton^ we have the ablest expo- nent and special defender of the Scottish realism. To fully appreciate his philosophy, as Dr. McCosh suggests, we must bear in mind the influence of four men upon his thinking: Aristotle, Reid, Kant, and Jacobi. Our interest here extends only to the influence exerted upon his philosophical thinking by Reid. This is manifest in his theory of perception and his doctrine of common sense. i. His theory of perception is intuitive or immediate * " Lectures on the Philosophy of the Human Mind," Hallo well, 1820, lees, xxv-xxvii. f Ibid. J "Lectures on Metaphysics," Edinburgh and London, 1870; Cf. also Reid's " Works," Notes and Dissertations, UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 51 perception.* The mind gazes immediately upon extra- mental reality. He differs from Reid, however, in ex- cluding from the objects immediately known, objects which are not in correlation to the bodily organism. According to Hamilton, the objects which the mind immediately perceives in sense-perception are the organ- ism, and the extra-bodily objects in correlation to the organism, i. e., extra-bodily objects in their resistance to our locomotive or muscular energy, f The grounds on which he bases the theory of immediate perception are, positively, the testimony of consciousness, J and, negatively, the sceptical consequences which he regards to be the inevitable result of a denial of this theory. 2. Reid's influence upon Hamilton is very marked indeed in his doctrine of common sense. Hamilton made an elaborate attempt not only to establish the legitimacy of the argument from common sense, and to point out the criteria of common-sense principles, but also to vindicate the use of the term "common sense.' The propriety of using the term" common sense " he tries to establish by an appeal to the history of philosophy. He traces the use of the word " from the dawn of specu- lation to the present day," finding it in use by nearly every philosopher. This historical survey evinces a patience and erudition which are simply remarkable. * " Metaphysics," vol ii, lees, xxiv-xxviii, also Reid's " Works," Note D. f Ibid. See in Note D other differences of a minor character, pp. 882-6. I Ibid. Reid's "Works, "Note A. 52 THE INFLUENCE OF REID'S PHILOSOPHY In the works of one hundred and six writers, he finds witnesses to the legitimacy of the term " common sense." Among these writers are numbered the greatest names in philosophy. As to the meaning and authority of common sense he says: Demonstration, if proof be possible at all, must ultimately rest upon certain fundamental propositions which must be accepted. These propositions are more on the order of facts, feelings, beliefs, than cognitions, because of their inexplicable character. Nevertheless, Hamilton calls them cognitions. Now, if they must be accepted, the question arises as to the authority for accepting them. The answer to this is: they must be accepted because they are the conditions sine qua non of knowledge, and to impeach them is to impeach the data of consciousness. To show that a denial of a certain proposition would impeach the integrity of an original datum of consciousness, is to argue from common sense. "Limiting, therefore, our consideration to the question of authority: how, it is asked, do these pri- mary propositions these cognitions at first hand these fundamental facts, feelings, beliefs, certify us of their own veracity ? To this the only possible answer is that as elements of our mental constitution as the essential conditions of our knowledge they must by us be accepted as true. To suppose their falsehood, is to suppose that we are created capable of intelligence,- in order to be made the victims of delusion: that God is a deceiver, and the root of our nature a lie. But such a supposition, if gratuitous, is manifestly illegitimate. For, on the contrary, the data of our original conscious- ness must, it is evident, in the first instantt be presumed UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 53 true. It is only if proved false, that their authority can, in consequence of that proof, be, in the second instance, disallowed. Speaking, therefore, generally, to argue from common sense is simply to show, that the denial of a given proposition would involve the denial of some original datum of consciousness: but as every original datum of consciousness is to be presumed true, that the proposition in question, as dependent on such a prin- ciple, must be admitted."* But still it may be urged: Why trust the deliverances of consciousness ? To this question Hamilton replies: "If, therefore, it can be shown on the one hand, that the deliverances of consciousness must philosophically be accepted, until their certain or probable falsehood has been positively evinced: and if, on the other hand, it cannot be shown that any attempt to discredit the veracity of consciousness has ever yet succeeded: it follows that, as philosophy now stands, the testimony of consciousness must be viewed as high above suspicion, and its declarations entitled to demand prompt and un- conditional assent, "f In regard to the first point it must be acknowledged that, at least, in the first instance, the veracity of con- sciousness must be accepted. We may not gratuitously assume that Nature works "in counteraction of her- self. " Unless there are reasons to the contrary, it is not to be supposed that our faculty of knowledge is "an instrument of illusion." But, secondly, even though in the outset the veracity of the deliverances of consciousness must be admitted, * Works," Note A, p. 743. t Ibid., p. 745. 54 THE INFLUENCE OF REID'S PHILOSOPHY ' ' it still remains competent to lead a proof that they are undeserving of credit." The question, however, arises as to how this is to be accomplished. This can only be done (i) by showing, inasmuch as there are quite a number of these primary data, that they immediately contradict each other, or (2) that they are indirectly con- tradictory, inasmuch as conclusions derived from them, and for which they are responsible, are mutually con- tradictory. This would prove the inconsistency of con- sciousness with itself, and, of course, as a consequence, its inconsistency with the unity of truth. But such con- tradiction or inconsistency, says Hamilton, has never yet been established. "No attempt to show that the data of consciousness are (either in themselves, or in their necessary consequences) mutually contradictory, has yet succeeded: and the presumption in favor of the truth of consciousness and the possibility of philosophy has therefore, never been redargued. In other words, an original, universal, dogmatic subversion of knowledge has hitherto been found impossible. " * We must, then, accept the primary deliverances of consciousness as true, and the argument from common sense which shows that a denial of a certain proposition discredits an original datum of consciousness must be regarded as legitimate. The essential marks which distinguish these original or fundamental cognitions or convictions from those which are derived, are four, viz., incomprehensibility, simplicity, necessity and absolute universality, and com- parative evidence and certainty. A conviction is in- comprehensible when it is merely given in consciousness * " Works," Note A, p. 746. UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 55 that its object is, and not why or how it is. A cognition or belief is simple when it is not compounded of other cognitions or beliefs. A cognition or belief is necessary or universal (these are coincident) when it is impossible to think it false. By comparative evidence and cer- tainty is meant, quoting from Aristotle, "If we know and believe through certain original principles, we must know and believe these with paramount certainty, for the very reason that we know and believe all else through them." These four marks, then, incompre- hensibility, simplicity, necessity and absolute universality, and comparative evidence and certainty, constitute the essential characters by which original cognition or beliefs are known.* Common-sense principles, then, are in- comprehensible, simple, necessary, and absolutely uni- versal -principles, which if an attempt be made to prove or disprove them would involve a resort to principles "neither more evident nor more certain." Hamilton made no such attempt as that of Reid's to classify, or to make a list of, these principles. However, he emphatically pronounces the immediate perceptions of self and of an extra-mental world of extended objects to be common-sense principles, for they are primary data of consciousness. Our interest here in Hamilton's philosophy, as before suggested, does not extend beyond his theory of per- ception and his doctrine of common sense. These are the features which ally him to Reid and the Scottish School. These we have found to be immediate or intuitive perception and the veracity of consciousness in * "Works," Note A, p. 754; " Metaphysics," lee. xxxviii. 56 THE INFLUENCE OF REID'S PHILOSOPHY its original deliverances in the form of "cognitions" or "beliefs." In France, the philosophy of Reid exerted considera- ble influence. It was first used by M. Royer-Collard * as a weapon against sensationalism and materialism. The philosophy of Condillac and the French Ideolo- gists was strongly established there. Collard saw that the sensationalism of Condillac rested upon the same foundation as that which underlay the scepticism of Hume; and, with Reid, he felt that if the premises be accepted the conclusion legitimately followed. The prem- ises of scepticism and sensationalism are the same, the "theory of ideas." The same means which Reid used for the overthrowal of these premises were used by Col- lard the theory of immediate perception and the prin- ciple of common sense meaning by common sense a sort of mental instinct. Another French philosopher on whose thinking Reid's philosophy exerted considerable influence was M. Victor Cousin, f the real father of eclecticism in France. He bor- rows largely from the Scottish and German schools of philosophy, but acknowledges the principal factor of this eclecticism to be taken from the Scottish philosophy. In the adoption of the inductive method, in basing phi- losophy upon psychology, in the use of the doctrine of common sense in a modified form, we see the in- fluence of Reid's philosophy upon the thinking of Cousin. * " Fragmens de Royer-Collard," Jouffroy's trans, of the works of Reid. t "Philosophic Ecossaise," Paris, 1846. UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 57 Th. Jouffroy,* the pupil of Cousin, was also greatly influenced by Reid's philosophy. He translated the works of Reid into French, and it was through his teaching, together with the teaching of Collard and Cousin, that the Scottish philosophy became for a while the prevailing philosophy in France. He, too, is an eclectic, but some of the positions of the Scottish School are prominent factors in his eclecticism. The application of the inductive method to the study of the phenomena of consciousness, and the common-sense at- titude toward the problem of substance, indicate the in- fluence of Reid and Stewart upon his thinking, f In Germany, Reid's influence upon philosophy amounts to very little indeed. Kant regarded his phi- losophy with more or less contempt. There are some evidences of its influence in the philosophy of Benecke. J In America, directly and indirectly (through his dis- ciples) Reid's philosophy has exerted great influence. Dr. Porter says: ''The Scottish philosophy has had a wide-spread influence in this country. The works of Reid were not so generally circulated on account of the pre-occupations of the American War for Independence and the organization of the new political union, 1770- 1800, but when the attention of thinking men was aroused to the practical consequences of the theological and political philosophy of England and France, the works of Reid were studied for a better system. As soon as Dugald Stewart appeared upon the arena, his * " Preface a la Traduction des CEuvres de Reid," 1835. f Cf. McCosh, " The Scottish Philosophy," pp. 302-3. J " Die Neue Psychologic," Berlin, 1845. 58 THE INFLUENCE OF REID'S PHILOSOPHY lectures were resorted to by a few favored American pupils, and his works were reprinted as fast as they ap- peared, and some of them became the favored text- books in our leading colleges."* Later, through the works of Hamilton, widely circulated in this country, and the works of prominent American thinkers identi- fied with the Scottish School, the essential principles of Reid's philosophy became widely known, being taught in many colleges. Among the American writers on philosophy, just referred to, Dr. James McCosh and Dr. Noah Porter may be mentioned. McCosh, f though differ- ing from Reid in points of minor importance, accepts with slight alterations the cardinal features of his philosophy. i. His theory of perception is intuitive or immediate perception. In sense-perception we have an immediate knowledge of extra-mental material objects. | These objects are the bodily organism, the various parts of which " as affected " are immediately perceived through the different senses; and extra-bodily material objects in correlation to the body, perceived specially through the muscular sense. "We may notice here that sense-perception gives us (i) Externality. We perceive all material objects as out of, and independent of, the perceiving mind. This is associated with (2) Extension. We perceive things as extended by all the senses, not only as Locke thought by sight and touch, but by smell, taste and hearing ; by * "Ueberweg's History of Philosophy," Appendix i, vol. ii, pp. 45 1 - 2 - f " Psychology," New York, 1886; " Realistic Philosophy," New York, 1887, 2 vols., etc. J "Psychology," pp. 20-69. UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 59 all these we know our affected organism as in a certain direction and so in space ; by taste and smell we know the palate and nostrils as affected, and by hearing, our ear as affected. (3) We perceive body exercising en- ergy. We do so especially by the muscular sense ; we find body resisting locomotive energy. Perhaps we have some vague sense of energy by all the senses : the ob- jects perceived seem to affect us. But the sense of power is specially given by our energy and the resistance to our energy."* These three cognitions Dr. McCosh calls primitive or intuitive cognitions. 2. His doctrine of " First and Fundamental Truths " evinces the influence of Reid. Demonstration, he says, cannot go on forever. We cannot prove all things by mediate evidence. We can show, however, that we are justified in making certain fundamental assumptions. Of these assumptions, which he calls fundamental truths, the tests are : self-evidence, necessity, and universality, f Dr. Porter's writings^ evince the influence of German speculative thought, as well as that of Reid and his School. However, the influence of the Scottish thinkers is predominant. As in Dr. McCosh's philosophy, this may be seen in his theory of perception and primary truths. i. His theory of perception is intuitive perception. The object is known immediately. The object thus known * " Psychology," p. 68. f "Realistic Philosophy," vol. i, pp. 33-43. Cf. also " Intui- tions of the Mind." J " The Human Intellect," New York, 1875; The Elements of Intellectual Science," New York, 1884. 60 THE INFLUENCE OF REID'S PHILOSOPHY is "the sensorium in some form of excited action." The eye, ear, nostril, hand, etc., "with the nerves at- tached as capable of the sentient function when acting in a living organism, are known by the collective term, the sensorium, or sensory." This sensorium is known immediately not only as a non-ego, but also as extended.* Extra-organic bodies are not known immediately. Our knowledge of them is "indirect or acquired, "f On this latter point he differs from Reid who holds to an im- mediate perception of extra-organic objects. 2. We have an intuitive knowledge of first principles. The criteria of such principles are: universality, necessity and logical independence and originality. J However, notwithstanding the wide influence exerted by the philosophy of Reid in Great Britain, France and America, his historical significance is not great. Cousin regarded him as the modern Socrates. This estimate of his historical position is true in one sense. Being the first philosopher to attempt to save philosophy from the scepticism of Hume, he occupies the same position in modern philosophy which Socrates holds in Greek phi- losophy in his opposition to the scepticism of the Sophists. But in his influence upon the subsequent development of philosophic thought, Reid cannot be compared with Socrates. To Kant must be awarded the honor of such a comparison. It was his great work which determined the main course of philosophy subsequent to Hume, just as the philosophizing of Socrates determined the * " Elements of Intellectual Science," p. 106. f Ibid., p. 155. J Ibid., pp. 416-45. UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 6l course of Greek philosophy, subsequent to the Sophists. Indeed, as in the philosophy of Socrates we find the best standpoint from which to survey the development of ancient philosophy from Thales to the Christian era, so in the philosophy of Kant we find the best standpoint from which to view the development of modern philoso- phy from Des Cartes to Von Hartmann. E. HERSHEY SNEATH. AN INQUIRY INTO THE HUMAN MIND ON THE PRINCIPLES OF COMMON SENSE, BY THOMAS REID, D. D. A n A. DEDICATION. THE RIGHT HONOURABLE JAMES, EARL OF FINDLATER AND SE AFIELD, CHANCELLOR OF THE UNIVERSITY OF OLD ABERDEEN. MY LORD, Though I apprehend that there are things, new and of some importance, in the following Inquiry, it is not without timidity that I have consented to the publication of it. The subject has been canvassed by men of very great penetration and genius: for who does not acknowledge Des Cartes, Malebranche, Locke, Berkeley, and Hume, to be such ? A view of the human understanding, so different from that which they have ex- hibited, will, no doubt, be condemned by many, without examination, as proceeding from temerity and vanity. But I hope the candid and discerning Few, who are capable of attending to the operations of their own minds, will weigh deliberately what is here advanced, before they pass sentence upon it. To such I appeal, as the only competent judges. If they disapprove, I am prob- ably in the wrong, and shall be ready to change my opinion upon conviction. If they approve, the Many will at last yield to their authority, as they always do. However contrary my notions are to those of the wri- ters I have mentioned, their speculations have been of great use to me, and seem even to point out the road which I have taken: and your Lordship knows, that the merit of useful discoveries is sometimes not more justly 65 66 THE PHILOSOPHY OF REID. due to those that have hit upon them, than to others that have ripened them, and brought them to the birth. I acknowledge, my Lord, that I never thought of call- ing in question the principles .commonly received with regard to the human understanding, until the "Treatise of Human Nature " was published in the year 1739. The ingenious author of that treatise upon the principles of Lo^ke wjio wasjio"sceptic hatrrr3uiTfafsystem of scep- ticism, which leaves no ground to believe" any one thing father than its contrary! His reasoning appeare~d to me to be just ; there was, therefore, aTliecessiTy to call in question the principles upon which it wasToundeTr; or to But can any ingenuous mind admit this sceptical sys- tem without reluctance ? I truly could not, my Lord ; for I am persuaded, that absolute scepticism is not more destructive of the faith of a Christia'n than of the science of a philosopher, and of the prudence of a man of common understanding. I am persuaded, that the \my\s\Jiwe_byfaith as well as the just; that, I if all belief could be laid asid~e7 piety, patrToHsm, friend- \ ship, parental affection, and private virtue, would appear j as ridiculous as knight-errantry ; and that the pursuits ' of pleasure, of ambition, and of avarice, jnust be grounded upon belief as well as those that are honour- able or virtuous. * "This doctrine of ideas" (says Dr. Reid, in a subsequent work) } " I once believed so firmly, as to embrace the whole of Berkeley's system in consequence of it ; till, finding other consequences to follow from it, which gave me more uneasiness than the want of a material world, it came into my mind, more than forty years ago, to put the question, What evidence have I for this doctrine, that all the objects of my knowledge are ideas in my own mind ? " Essays on the Intellectual Powers, Ess. II. ch. x. p. 162. In like manner, Kant informs us, that it was by Hume's sceptical inferences, in regard to the causal nexus, that he also ** was first roused from his dogmatic slumber." See the " Prolegomena," p. 13. H. THE PHILOSOPHY OF REID. 67 The day-labourer toils at his work, in the belief that he shall receive his wages at night ; and, if he had not this belief, he'would not toil. We may venture to say, that even the author of this sceptical system wrote it in the belief that it should be read and regarded. I hope he wrote it in the belief also that it would be useful to man- kind; and, perhaps, it may prove so at last. For I con- ceive the sceptical writers to be a set of men whose busi- ness it is to pick holes in the fabric of knowledge wher- ever it is weak and faulty ; and, when these places are properly repaired, the whole building becomes more firm and solid than it was formerly. For my own satisfaction, I entered into a serious ex- amination of the principles upon which this sceptical sys- tem is built ; and was not a little surprised to find, that it leans with its whole weight upon a hypothesis, which is ancient indeed, and hath been very generally received by philosophers, but of which I could find no solid proof. The hypothesis I mean is, TrTal nothing is perceived but what is in the_mmd wnich perceives it : That we do not really perceive things that are external, but only certain images and pictures of them impiinted upon thlTTmn d, which are called impressions and ideas. If this be true, supposing certain impressions and ideas to exist in my mind, I cannot, from their existence, in- fer the existence of anything else : my impressions and ideas are the only existences of which I can have any knowledge or conception; and they are such fleeting and transitory beings, that they can have no existence at all, any longer than I am conscious of them. So that, upon this hypothesis, the whole universe about me, bodies and spirits, sun, moon, stars, and earth, friends and relations, all things without exception, which I imagined to have a permanent existence, whether I thought of them or not, vanish at once ; ' ' And, like the baseless fabric of a vision, Leave not a track behind." 68 THE PHILOSOPHY OF REID. I thought it unreasonable, my Lord, upon the author- ity of philosophers, to admit a hypothesis which, in my opinion, overturns all philosophyTall religion and virtue, and all common"~sense and, finding that alPthe sys- temsToncerning theliuman understanding which I was acquainted with, were built .upon this hypothesis, I re- solved to inquire into this subject anew, without regard to any Ji^pottiesis. ^Vhat I now humbly present to your Lordship, is the fruit of this inquiry, so far only as it regards the five senses: in which I claim no other merit than that of having given great attention to the operations of my own mind, and of having expressed, with all the perspicuity I was able, what I conceive every man, who gives the same attention, will feel and perceive. The productions of im- agination require a genius which soars above the com- mon rank ; but the treasures of knowledge are commonly buried deep, and may be reached by those drudges who can dig with labour and patience, though they have not wings to fly. The experiments that were to be made in this investigation suited me, as they required no other expense but that of time and attention, which I could bestow. The leisure of an academical life, disengaged from the pursuits of interest and ambition ; the duty of my profession, which obliged me to give prelections on these subjects to the youth ; and an early inclination to specu- lations of this kind, have enabled me, as I flatter myself, to give a more minute attention to the subject of this in- quiry, than has been given before. My thoughts upon this subject were, a good many years ago, put together in another form, for the use of my pu- pilf and afterwards were submitted to the judgment of a private philosophical society,* of which I have the honour to be a member, A great part of this Inquiry was hon- oured even by your Lordship's perusal. And the en- * Aberdeen Philosophical Society founded by Reid and Dr. John Gregory. S. THE PHILOSOPHY OF REID. 69 couragement which you, my Lord, and others, whose friendship is my boast, and whose judgment I reverence, were pleased to give me, counterbalanced my timidity and diffidence, and determined me to offer it to the public. If it appears to your Lordship to justify the common sense and reason of mankind, against the sceptical sub- tilties which, in this age, have endeavoured to put them out of countenance if it appears to throw any new light upon one of the noblest parts of the divine work- manship your Lordship's respect for the arts and sci- ences, and your attention to everything which tends to the improvement of them, as well as to everything else that contributes to the felicity of your country, leave me no room to doubt of your favourable acceptance of this essay, as the fruit of my industry in a profession where- in I was accountable to your Lordship ; and as a testi- mony of the great esteem and respect wherewith I have the honour to be, My Lord, your Lordship's most obliged and most de- voted Servant, THO. REID. AN INQUIRY INTO THE HUMAN MIND. CHAPTER I. INTRODUCTION. Section /. THE IMPORTANCE OF THE SUBJECT, AND THE MEANS OF PROSECUTING IT. THE fabric of the human mind is curious and won- derful, as well as that of the human body. The facul- ties of the one are with no less wisdom adapted to their several ends than the organs of the other. Nay, it is reasonable to think, that, as the mind is a nobler work and of a higher order than the body, even more of the wisdom and skill of the divine Architect hath been em- ployed in its structure. It is, therefore, a subject highly worthy of inquiry on its own account, but still more worthy on account of the extensive influence which the knowledge of it hath over every other branch of science. In the arts and sciences which have least connection with the mind, its faculties are the engines which we must employ; and the better we understand their nature and use, their defects and disorders, the more skilfully we shall apply them, and with the greater success. But in the noblest arts, the mind is also the subject upon which we operate. The painter, the poet, the actor, the orator, the moralist, and the statesman, attempt to oper- 70 SEC. I.] THE PHILOSOPHY OF REID. 71 ate upon the mind in different ways, and for different ends; and they succeed according as they touch properly the strings of the human frame. Nor can their several arts ever stand on a solid foundation, or rise to the dignity of science, until they are built on the principles of the human constitution. Wise men now agree, or ought to agree, in this, that there is but one way to the knowledge of nature's works the way of observation and experiment. By our con- stitution, we have a strong propensity to trace particular facts and observations to general rules, and to apply such general rules to account for other effects, or to di- rect us in the production of them. This procedure of the understanding is familiar to every human creature in the common affairs of life, and it is the only one by which any real discovery in philosophy can b,e made. The man who first discovered that cold freezes water, and that heat turns it into vapour, proceeded on the same general principles, and in the same method by which Newton discovered the law of gravitation and the properties of light. His regulce philosophandi are maxims of common sense, and are practised every day in com- mon life; and he who philosophizes by other rules, either concerning the material system or concerning the mind, mistakes his aim. Conjectures and theories are the creatures of men, and will always be found very unlike the creatures of God. If we would know the works of God, we must consult themselves with attention and humility, without daring to add anything of ours to what they declare. A just interpretation of nature is the only sound and orthodox! philosophy: whatever we add of our own, is apocryphal, and of no authority. All our curious theories of the formation of the earth, of the generation of animals, of the origin of natural and moral evil, so far as they go beyond a just induction from facts, are vanity and folly, no less than the Vortices 72 THE PHILOSOPHY OF REID. ;CH. I. of Des Cartes, or the Archaeus of Paracelsus. Perhaps the philosophy of the mind hath been no less adulterated by theories, than that of the material system. The theory of Ideas is indeed very ancient, and hath been very universally received; but, as neither of these titles can give it authenticity, they ought not to screen it from a free and candid examination; especially in this age, when it hath produced a system of scepticism that seems to triumph over all science, and even over the dictates of common sense. All that we know of the body, is owing to anatomical dissection and observation, and it must be by an anat- omy of the mind that we can discover its powers and principles. Section IL THE IMPEDIMENTS TO OUR KNOWLEDGE OF THE MIND. But it must be acknowledged, that this kind of anat- omy is much more difficult than the other; and, there- fore, it needs not seem strange that mankind have made less progress in it. To attend accurately to the opera- tions of our minds, and make them an object of thought, is no easy matter even to the contemplative, and to the bulk of mankind is next to impossible. An anatomist who hath happy opportunities, may have access to examine with his own eyes, and with equal ac- curacy, bodies of all different ages, sexes, and conditions; so that what is defective, obscure or preternatural in one, may be discerned clearly and in its most perfect state in another. But the anatomist of the mind cannot have the same advantage. It is his own mind only that he can examine with any degree of accuracy and distinct- ness. This is the only subject he can look into. He may, from outward signs, collect the operations of other minds; but these signs are for the most part ambiguous, and must be interpreted by what he perceives within himself. SKC.H.] THE PHILOSOPHY OF REID. 73 So that, if a philosopher could delineate to us, dis- tinctly and methodically, all the operations of the think- ing principle within him, which no man was ever able to do, this would be only the anatomy of one particular subject; which would be both deficient and erroneous, if applied to human nature in general. For a little re- flection may satisfy us, that the difference of minds is greater than that of any other beings which we consider as of the same species. Of the various powers and faculties we possess, there are some which nature seems both to have planted and reared, so as to have left nothing to human industry. Such are the powers which we have in common with the brutes, and which are necessary to the preservation of the individual, or the continuance of the kind. There are other powers, of which nature hath only planted the seeds in our minds, but hath left the rearing of them to human culture. It is by the proper culture of these that we are capable of all those improvements in intellectuals, in taste, and in morals, which exalt and dignify human nature; while, on the other hand, the neglect or perversion of them makes its degeneracy and corruption. The two-legged animal that eats of nature's dainties, what his taste or appetite craves, and satisfies his thirst at the crystal fountain, who propagates his kind as occasion and lust prompt, repels injuries, and takes alternate labour and repose, is, like a tree in the forest, purely of nature's growth. But this same savage hath within him the seeds of the logician, the man of taste and breeding, the orator, the statesman, the man of virtue, and the saint; which seeds, though planted in his mind by na- ture, yet, through want of culture and exercise, must lie for ever buried, and be hardly perceivable by himself or by others. The lowest degree of social life will bring to light some of those principles which lay hid in the savage state; 74 THE PHILOSOPHY OF REID. [Cn. I. and, according to his training, and company, and man- ner of life, some of them, either by their native vigor, or by the force of culture, will thrive and grow up to great perfection, others will be strangely perverted from their natural form, and others checked, or perhaps quite eradicated. This makes human nature so various and multiform in the individuals that partake of it, that, in point of morals and intellectual endowments, it fills up all that gap which we conceive to be between brutes and devils below, and the celestial orders above; and such a pro- digious diversity of minds must make it extremely diffi- cult to discover the common principles of the species. The language of philosophers, with regard to the original faculties of the mind, is so adapted to the pre- vailing system, that it cannot fit any other; like a coat that fits the man for whom it was made, and shews him to advantage, which yet will sit very awkward upon one of a different make, although perhaps as handsome and as well proportioned. It is hardly possible to make any innovation in our philosophy concerning the mind and its operations, without using new words and phrases, or giving a different meaning to those that are received a liberty which, even when necessary, creates prejudice and misconstruction, and which must wait the sanction of time to authorize it; for innovations in language, like those in religion and government, are always suspected and disliked by the many, till use hath made them famil- iar, and prescription hath given them a title. If the original perceptions and notions of the mind were to make their appearance single and unmixed, as we first received them from the hand of nature, one ac- customed to reflection would have less difficulty in tracing them; but before we are capable of reflection, they are so mixed, compounded, and decompounded, by habits, as- sociations, and abstractions, that it is hard to know what they were originally. The mind may, in this respect, SEC. II.] THE PHILOSOPHY OF REID, 75 be compared to an apothecary or a chemist, whose materials indeed are furnished by nature; but, for the purposes of his art, he mixes, compounds, dissolves, evaporates, and sublimes them, till they put on a quite different appearance; so that -it is very difficult to know what they were at first, and much more to bring them back to their original and natural form. And this work of the mind is not carried on by deliberate acts of mature reason, which we might recollect, but by means of in- stincts, habits, associations, and other principles, which operate before we come to the use of reason; so that it is extremely difficult for the mind to return upon its own footsteps, and trace back those operations which have employed it since it first began to think and to act. Could we obtain a distinct and full history of all that hath past in the mind of a child, from the beginning of life and sensation, till it grows up to the use of reason how its infant faculties began to work, and how they brought forth and ripened all the various notions, opinions and sentiments which we find in ourselves when we come to be capable of reflection this would be a treasure of natural history, which would probably give more light into the human faculties, than all the systems of philosophers about them since the beginning of the world. But it is in vain to wish for what nature has not put within the reach of our power. Reflection, the only instrument by which we can discern the powers of the mind, comes too late to observe the progress of nature, in raising them from their infancy to perfection. It must therefore require great caution, and great application of mind, for.a man that is grown up in all the prejudices of education, fashion, and philosophy, to unravel his notions and opinions, till he find out the simple and original principles of his constitution, of which no account can be given but the will of our Maker. This may be truly called an analysis of the human faculties; and, till this is performed, it is in vain 76 THE PHILOSOPHY OF REID. [CH. I. we expect any just system of the mind that is, an enumeration of the original powers and laws of our con- stitution, and an explication from them of the various phenomena of human nature. Success in an inquiry of this kind, it is not in human power to command ; but, perhaps, it is possible, by caution and humility, to avoid error and delusion. The labyrinth may be too intricate, and the thread too fine, to be traced through all its windings; but, if we stop where we can trace it no farther, and secure the ground we have gained, there is no harm done; a quicker eye may in time trace it farther. It is genius, and not the want of it, that adulterates philosophy, and fills it with error and false theory. A v creative imagination disdains the mean offices of dig- ging for a foundation, of removing rubbish, and carry- ing materials; leaving these servile employments to the drudges in science, it plans a design, and raises a fabric. . Invention supplies materials where they are wanting, and fancy adds colouring and every befitting ornament. The work pleases the eye, and wants nothing but solidity and a good foundation. It seems even to vie with the works of nature, till some succeeding architect blows it into rubbish, and builds as goodly a fabric of his own in its place. Happily for the present age, the castle-builders employ themselves more in romance than in philosophy. That is undoubtedly their province, and in those regions the offspring of fancy is legitimate, but in philosophy it is all spurious. Section III. THE PRESENT STATE OF THIS PART OF PHILOSOPHY OF DES CARTES, MALEBRANCHE, AND LOCKE. That our philosophy concerning the mind and its faculties is but in a very low state, may be reasonably conjectured even by those who never have narrowly ex- SEC. III.] THE PHILOSOPHY OF REID. 77 amined it. Are there any principles, with regard to the mind, settled with that perspicuity and evidence which attends the principles of mechanics, astronomy and optics ? These are really sciences built upon laws of nature which universally obtain. What is discovered in them is no longer matter of dispute: future ages may add to it ; but, till the course of nature be changed, what is already established can never be overturned. But when we turn our attention inward, and consider the phaenomena of human thoughts, opinions, and percep- tions, and endeavour to trace them to the general laws and the first principles of our constitution, we are im- mediately involved in darkness and perplexity; and, if common sense, or the principles of education, hap- pen not to be stubborn, it is odds but we end in absolute scepticism. Des Cartes, finding nothing established in this part of philosophy, in order to lay the foundation of it deep, resolved not to believe his own existence till he should be able to give a good reason for it. He was, perhaps, the first that took up such a resolution; but, if he could indeed have effected his purpose, and really become diffident of his existence, his case would have been de- plorable, and without any remedy from reason or philos- ophy. A man that disbelieves his own existence, is surely as unfit to be reasoned with as a man that believes he is made of glass. There may be disorders in the human frame that may produce such extravagancies, but they will never be cured by reasoning. Des Cartes, in- deed, would make us believe that he got out of this delirium by this logical argument, Cogito, ergo sum; but it is evident he was in his senses all the time, and never seriously doubted of his existence; for he takes it for granted in this argument, and proves nothing at all. I am thinking, says he therefore, I am. And is it not as good reasoning to say, I am sleeping therefore, I am ? or, I am doing nothing therefore, I am ? If a 78 THE PHILOSOPHY OF REID. [Cn. I. body moves, it must exist, no doubt; but, if it is at rest it must exist likewise.* Perhaps Des Cartes meant not to assume his own ex- istence in this enthymeme, but the existence of thought; and to infer from that the existence of a mind, or subject of thought. But why did he not prove the existence of his thought ? Consciousness, it may be said, vouches that. But who is voucher for consciousness ? Can any man prove that his consciousness may not deceive him ? No man can; nor can we give a better reason for trusting to it, than that every man, while his mind is sound, is determined, by the constitution of his nature, to give implicit belief to it, and to laugh at or pity the man who doubts its testimony. And is not every man, in his wits, as much determined to take his existence upon trust as his consciousness ? The other proposition assumed in this argument, That thought cannot be without a mind or subject, is liable to the same objection: not that it wants evidence but that its evidence is no clearer, nor more immediate, than that of the proposition to be proved by it. And, taking all these propositions together I think; I am conscious; Everything that thinks, exists; I exist would not every sober man form the same opinion of the man who seriously doubted any one of them ? And if he was his friend, would he not hope for his cure from physic and good regimen, rather than from metaphysic and logic ? But supposing it proved, that my thought and my consciousness must have a subject, and consequently that I exist, how do I know that all that train and succession of thoughts which I remember belong to one subject, and that the I of this moment is the very individual I of yesterday and of times past ? * The nature ot the Cartesian Doubt and its solution is here mis- apprehended. II. See note, I. P., Essay ii., ch. 8. SEC. III.] THE PHILOSOPHY OF REID. 79 Des Cartes did not think proper to start this doubt ; but Locke has done it ; and, in order to resolve it, gravely determines that personal identity consists in consciousness that is, if you are conscious that you did such a thing a twelvemonth ago, this consciousness makes you to be the very person that did it. Now conscious- ness of what is past can signify nothing else but the re- membrance that I did it ; so that Locke's principle must be, That identity consists in remembrance ; and, conse- quently, a man must lose his personal identity with re- gard to everything he forgets. Nor are these the only instances whereby our philos- ophy concerning the mind appears to be very fruitful in creating doubts, but very unhappy in resolving them. Des Cartes, Malebranche, and Locke, have all em- ployed their genius and skill to prove the existence of a material world : and with very bad success. Poor untaught mortals believe undoubtedly that there is a sun, moon, and stars ; an earth, which we inhabit ; country, friends, and relations, which we enjoy ; land, houses, and movables, which we possess. But philos- ophers, pitying the credulity of the vulgar, resolve to have no faith but what is founded upon reason.* They apply to philosophy to furnish them with reasons for the belief of those things which all mankind have believed, without being able to give any reason for it. And surely one would expect, that, in matters of such importance, the proof would not be difficult : but it is the most dif- ficult thing in the world. For these three great men, with the best good will, have not been able, from all the treasures of philosophy, to draw one argument that is fit to convince a man that can reason, of the existence of any one thing without him. Admired Philosophy! * Reason is here employed, by Reid, not as a synonyme for Com- mon Sense, (yov, locus principiorum) and as he himself more cor- rectly employs it in his later works, but as equivalent to Reasoning, (dictvoia, discursus mentalis.) See Note A. H. 8o THE PHILOSOPHY OF REID. [CH. I. daughter of light ! parent of wisdom and knowledge ! if thou art she, surely thou hast not yet arisen upon the human mind, nor blessed us with more of thy rays than are sufficient to shed a darkness visible upon the human faculties, and to disturb that repose and security which happier mortals enjoy, who never approached thine altar, nor felt thine influence ! But if, indeed, thou hast not power to dispel those clouds and phantoms which thou hast discovered or created, withdraw this penurious and malignant ray; I despise Philosophy, and renounce its guidance let my soul dwell with Common Sense.* Section IV. APOLOGY FOR THOSE PHILOSOPHERS. But, instead of despising the dawn of light, we ought rather to hope for its increase : instead of blaming the philosophers I have mentioned for the defects and blem- ishes of their system we ought rather to honour their mem- ories, as the first discoverers of a region in philosophy formerly unknown ; and however lame and imperfect the system may be, they have opened the way to future dis- coveries, and are justly entitled to a great share in the merit of them. They have removed an infinite deal of dust and rubbish, collected in the ages of scholastic soph- istry, which had obstructed the way. They have put us in the right road that of experience and accurate re- flection. They have taught us to avoid the snares of am- biguous and ill-defined words, and have spoken and thought upon this subject with a distinctness and perspi- cuity formerly unknown. They have made many open- ings that may lead to the discovery of truths which they did not reach, or to the detection of errors in which they were involuntarily entangled. * Mr. Stewart very justly censures the vagueness and ambiguity of this passage. Elem, vol ii., ch. i., 3, p. 92, 8vo editions. H- SBC.V.] THE PHILOSOPHY OF REID. 8l It may be observed, that the defects and blemishes in the received philosophy concerning the mind, which have most exposed it to the contempt and ridicule of sensible men, have chiefly been owing to this that the votaries of this Philosophy, from a natural prejudice in her fa- vour, have endeavoured to extend her jurisdiction beyond its just limits, and to call to her bar the dictates of Com- mon Sense. But these decline this jurisdiction ; they dis- dain the trial of reasoning, and disown its authority; they neither claim its aid, nor dread its attacks. In this unequal contest betwixt Common Sense and Philosophy, the latter will always come off both with dishonour and loss; nor can she ever thrive till this rival- ship is dropt, these encroachments given up, and a cordial friendship restored: for, in reality, Common Sense holds nothing of Philosophy, nor needs her aid. But, on the other hand, Philosophy (if I may be per- mitted to change the metaphor) has no other root but the principles of Common Sense ; it grows out of them, and draws its nourishment from them. Severed from this root, its honours wither, its sap is dried up, it dies and rots. The philosophers of the last age, whom I have men- tioned, did not attend to the preserving this union and subordination so carefully as the honour and interest of philosophy required: but those of the present have waged open war with Common Sense, and hope to make a complete conquest of it by the subtilties of Philosophy an attempt no less audacious and vain than that of the giants to dethrone almighty Jove. Section V. OF BISHOP BERKELEY THE "TREATISE OF HUMAN NA- TURE" AND OF SCEPTICISM. The present age, I apprehend, has not produced two more acute or more practised in this part of philosophy, 82 THE PHILOSOPHY OF REID. [Cii. I. than the Bishop of Cloyne, and the author of the " Treatise of Human Nature." The first was no friend to scepticism, but had that warm concern for religious and moral principles which became his order : yet the result of his inquiry was a serious conviction that there is no such thing as a material world nothing in nature but spirits and ideas; and that the belief of material sub- stances, and of abstract ideas, are the chief causes of all our errors in philosophy, and of all infidelity and heresy in religion. His arguments are founded upon the principles which were formerly laid down by Des Cartes, Malebranche, and Locke, and which have been very generally received. And the opinion of the ablest judges seems to be, that they neither have been, nor can be confuted; and that he hath proved by unanswerable arguments what no man in his senses can believe. The second proceeds upon the same principles, but carries them to their full length; and, as the Bishop un- did the whole material world, this author, upon the same grounds, undoes the world of spirits, and leaves nothing in nature but ideas and impressions, without any sub- ject on which they may be impressed. It seems to be a peculiar strain of humour in this author, to set out in his introduction by promising, with a grave face, no less than a complete system of the sciences, upon a foundation entirely new to wit, that of human nature when the intention of the whole work is to shew, that there is neither human nature nor science in the world. It may perhaps be unreasonable to com- plain of this conduct in an author who neither believes his own existence nor that of his reader; and therefore could not mean to disappoint him, or to laugh at his credulity. Vet I cannot imagine that the author of the ' ' Treatise of Human Nature " is so sceptical as to plead this apology. He believed, against his principles, that he should be read, and that he should retain his personal SEC. V.] THE PHILOSOPHY OF REID. 83 identity, till he reaped the honour and reputation justly due to his metaphysical acumen. Indeed, he ingeniously acknowledges, that it was only in solitude and retirement that he could yield any assent to his own philosophy; society, like daylight, dispelled the darkness and fogs of scepticism, and made him yield to the dominion of common sense. Nor did I ever hear him charged with doing anything, even in solitude, that argued such a de- gree of scepticism as his principles maintain. Surely if his friends apprehended this, they would have the charity never to leave him alone. Pyrrho the Elean, the father of this philosophy, seems to have carried it to greater perfection than any of his successors : for, if we may believe Antigonus the Carystian, quoted by Diogenes Laertius, his life cor- responded to his doctrine. And, therefore, if a cart run against him, or a dog attacked him, or if he came upon a precipice, he would not stir a foot to avoid the danger, giving no credit to his senses. But his attendants, who, happily for him, were not so great sceptics, took care to keep him out of harm's way; so that he lived till he was ninety years of age. Nor is it to be doubted but this author's friends would have been equally careful to keep him from harm, if ever his principles had taken too strong a hold of him. It is probable the "Treatise of Human Nature" was not written in company; yet it contains manifest indica- tions that the author every now and then relapsed into the faith of the vulgar, and could hardly, for half a dozen pages, keep up the sceptical character. In like manner, the great Pyrrho himself forgot his principles on some occasions; and is said once to have been in such a passion with his cook, who probably had not roasted his dinner to his mind, that with the spit in his hand, and the meat upon it, he pursued him even into the market-place. It is a bold philosophy that rejects, without ceremony, 84 THE PHILOSOPHY OF REID. [Cn. I. principles which irresistibly govern the belief and the conduct of all mankind in the common concerns of life; and to which the philosopher himself must yield, after he imagines he hath confuted them. Such principles are older, and of more authority, than Philosophy: she rests upon them as her basis, not they upon her. If she could overturn them, she must be buried in their ruins; but all the engines of philosophical subtil ty are too weak for this purpose; and the attempt is no less ridiculous than if a mechanic should contrive an axis in peritrochio to remove the earth out of its place; or if a mathematician should pretend to demonstrate that things equal to the same thing are not equal to one another. Zeno endeavoured to demonstrate the impossibility of motion; Hobbes, that there was no difference between right and wrong; and this author, that no credit is to be given to our senses, to our memory, or even to demon- stration. Such philosophy is justly ridiculous, even to those who cannot detect the fallacy of it. It can have no other tendency, than to shew the acuteness of the so- phist, at the expense of disgracing reason and human nature, and making mankind Yahoos. Section VI. OF THE "TREATISE OF HUMAN NATURE." There are other prejudices against this system of hu- man nature, which, even upon a general view, may make one diffident of it. Des Cartes, Hobbes, and this author, have each of them given us a system of human nature; an undertak- ing too vast for any one man, how great soever his ge- nius and abilities may be. There must surely be reason to apprehend, that many parts of human nature never came under their observation; and that others have been stretched and distorted, to fill up blanks, and complete SEC. VI.] THE PHILOSOPHY OF REID. 85 the system. Christopher Columbus, or Sebastian Cabot, might almost as reasonably have undertaken to give us a complete map of America. There is a certain character and style in Nature's works, which is never attained in the most perfect imi- tation of them. This seems to be wanting in the systems of human nature I have mentioned, and particularly in the last. One may see a puppet make variety of motions and gesticulations, which strike much at first view ; but when it is accurately observed, and taken to pieces, our admiration ceases: we comprehend the whole art of the maker. How unlike is it to that which it represents ! What a poor piece of work compared with the body of a man, whose structure the more we know, the more won- ders we discover in it, and the more sensible we are of our ignorance ! Is the mechanism of the mind so easily comprehended, when that of the body is so difficult ? Yet, by this system, three laws of association, joined to a few original feelings, explain the whole mechanism of sense, imagination, memory, belief, and of all the actions, and passions of the mind. Is this the man that Na- ture made ? I suspect it is not so easy to look behind the scenes in Nature's work. This is a puppet, surely, contrived by too bold an apprentice of Nature, to mimic her work. It shews tolerably by candle-light ; but, brought into clear day, and taken to pieces, it will ap- pear to be a man made with mortar and a trowel. The more we know of other parts of nature, the more we like and approve them. The little I know of the planet- ary system, of the earth, which we inhabit ; of minerals, vegetables, and animals ; of my own body ; and of the laws which obtain in these parts of nature opens to my mind grand and beautiful scenes, and contributes equally to my happiness and power. But, when I look within, and consider the mind itself, which makes me capable of all these prospects and enjoyments if it is, indeed, what the " Treatise of Human Nature" makes it I find 86 THE PHILOSOPHY OF REID. [Cn. I. I have been only in an enchanted castle, imposed upon by spectres and apparitions. I blush inwardly to think how I have been deluded ; I am ashamed of my frame, and can hardly forbear expostulating with my destiny. Is this thy pastime, O Nature, to put such tricks upon a silly creature, and then to -take off the mask, and shew him how he hath been befooled ? If this is the philo- sophy of human nature, my soul, enter thou not into her secrets ! It is surely the forbidden tree of knowledge ; I no sooner taste of it, than I perceive myself naked, and stript of all things yea, even of my very self. I see myself, and the whole frame of nature, shrink into fleet- ing ideas, which, like Epicurus's atoms, dance about in emptiness. Section VIL THE SYSTEM OF ALL THESE AUTHORS IS THE SAME, AND LEADS TO SCEPTICISM. But what if these profound disquisitions into the first principles of human nature, do naturally and necessarily plunge a man into this abyss of scepticism ? May we not reasonably judge so from what hath happened ? Des Cartes no sooner began to dig in this mine, than scepti- cism was ready to break in upon him. He did what he could to shut it out. Malebranche and Locke, who dug deeper, found the difficulty of keeping out this enemy still to increase; but they laboured honestly in the design. Then Berkeley, who carried on the work, despairing of securing all, bethought himself of an expedient: By giving up the material world, which he thought might be spared without loss, and even with advantage, he hoped, by an impregnable partition, to secure the world of spirits. But alas ! the "Treatise of Human Nature" wantonly sapped the foundation of this partition, and drowned all in one universal deluge. These facts, which are undeniable, do, indeed, give SEC. VIII.] THE PHILOSOPHY OF REID. 8? reason to apprehend that Des Cartes' system of the hu- man understanding, which I shall beg leave to call the ideal system, and which, with some improvements made by la- ter writers, is now generally received, hath some original defect; that this scepticism is inlaid in it, and reared along with it : and, therefore, that we must lay it open to the foundation, and examine the materials, before we can expect to raise any solid and useful fabric of know- ledge on this subject. Section VIII. WE OUGHT NOT TO DESPAIR OF A BETTER. But is this to be despaired of, because Des Cartes and his followers have failed ? By no means. This pusilla- nimity would be injurious to ourselves and injurious to truth. Useful discoveries are sometimes indeed the effect of superior genius, but more frequently they are the birth of time and of accidents. A traveller of good judgment may mistake his way, and be unawares led into a wrong track; and while the road is fair before him, he may go on without suspicion and be followed by others; but, when it ends in a coal-pit, it requires no great judgment to know that he hath gone wrong, nor perhaps to find out what misled him. In the meantime, the unprosperous state of this part of philosophy hath produced an effect, somewhat dis- couraging indeed to any attempt of this nature, but an effect which might be expected, and which time only and better success can remedy. Sensible men, who never will be sceptics in matters of common life, are apt to treat with sovereign contempt everything that hath been said, or is to be said, upon this subject. It is meta- physic, say they : who minds it ? Let scholastic sophis- ters entangle themselves in their own cobwebs ; I am re- 88 THE PHILOSOPHY OF REID. [C H . I.. SEC. VIII. solved to take my own existence, and the existence of other things, upon trust ; and to believe that snow is cold, and honey sweet, whatever they may say to the contrary. He must either be a fool, or want to make a fool of me, that would reason me out of my reason and senses. I confess I know not what a sceptic can answer to this, nor by what good argument he can plead even for a hear- ing ; for either his reasoning is sophistry, and so deserves contempt ; or there is no truth in human faculties and then why should we reason ? If, therefore, a man find himself intangled in these meta- physical toils, and can find no other way to escape, let him bravely cut the knot which he cannot loose, curse metaphysic, and dissuade every man from meddling with it ; for, if I have been led into bogs and quagmires by following an ignis fatuus, what can I do better than to warn others to beware of it? If philosophy contradicts herself, befools her votaries, and deprives them of every object worthy to be pursued or enjoyed, let her be sent back to the infernal regions from which she must have had her original. But is it absolutely certain that this fair lady is of the party ? Is it not possible she may have been misrepre- sented? Have not men of genius in former ages often made their own dreams to pass for her oracles? Ought she then to be condemned without any further hearing ? This would be unreasonable. I have found her in all other matters an agreeable companion, a faithful coun- sellor, a friend to common sense, and to the happiness of mankind. This justly entitles her to my correspond- ence and confidence, till I find infallible proofs of her infidelity. CH. II., SEC. I. THE PHILOSOPHY OF REID. 89 CHAPTER II. OF SMELLING. Section I. THE ORDER OF PROCEEDING OF THE MEDIUM AND ORGAN OF SMELL. IT is so difficult to unravel the operations of the hu- man understanding, and to reduce them to their first principles, that we cannot expect to succeed in the at- tempt, but by beginning with the simplest, and proceed- ing by very cautious steps to the more complex. The five external senses may, for this reason, claim to be first considered in an analysis of the human faculties. And the same reason ought to determine us to make a choice even among the senses, and to give the precedence, not to the noblest or most useful, but to the simplest, and that whose objects are least in danger of being mis- taken for other things. In this view, an analysis of our sensations may be carried on, perhaps with most ease and distinctness, by taking them in this order: Smelling, Tasting, Hearing, Touch, and, last of all, Seeing. Natural philosophy informs us, that all animal and vegetable bodies, and probably all or most other bodies, while exposed to the air, are continually sending forth effluvia of vast subtilty, not only in their state of life and growth, but in the states of fermentation and putre- faction. These volatile particles do probably repel each other, and so scatter themselves in the air, until they meet with other bodies to which they have some chemi- cal affinity, and with which they unite, and form new concretes. All the smell of plants, and of other bodies, 90 THE PHILOSOPHY OF REID. LCH. II. is caused by these volatile parts, and is smelled wherever they are scattered in the air : and the acuteness of smell in some animals, shews us, that these effluvia spread far, and must be inconceivably subtile. Whether, as some chemists conceive, every species of bodies hath a spiritus rector, a kind of soul, which causes the smell and all the specific virtues of that body, and which, being extremely volatile, flies about in the air in quest of a proper receptacle, I do not inquire. This, like most other theories, is perhaps rather the product of imagination than of just induction. But that all bodies are smelled by means of effluvia which they emit, and which are drawn into the nostrils along with the air, there is no reason to doubt. So that there is mani- fest appearance of design in placing the organ of smell in the inside of that canal, through which the air is con- tinually passing in inspiration and expiration. Anatomy informs us, that the membrana pituitaria, and the olfactory nerves, which are distributed to the villous parts of this membrane, are the organs destined by the wisdom of nature to this sense; so that when a body emits no effluvia, or when they do not enter into the nose, or when the pituitary membrane or olfactory nerves are rendered unfit to p'erform their office, it cannot be smelled. Yet, notwithstanding this, it is evident that neither the organ of smell, nor the medium, nor any motions we can conceive excited in the membrane^ above mentioned, or in the nerve or animal spirits, do in the least resem- ble the sensation of smelling; nor could that sensation of itself ever have led us to think of nerves, animal spirits, or effluvia. Section II. THE SENSATION CONSIDERED ABSTRACTLY. Having premised these things with regard to the me- dium and organ of this sense, let us now attend careful- SEC. II.] THE PHILOSOPHY OF REID. 91 ly to what the mind is conscious of when we smell a rose or a lily; and, since our language affords no other name for this sensation, we shall call it a smell or odour, care- fully excluding from the meaning of those names every- thing but the sensation itself, at least till we have ex- amined it. ^ Suppose a person who never had this sense before, to receive it all at once, and to smell a rose can he per- ceive any similitude or agreement between the smell and \ the rose? or indeed between it and any other object what- soever? Certainly he cannot. He finds himself affected in a new way, he knows not why or from what cause. Like a man that feels some pain or pleasure, formerly un- known to him, he is conscious that he is not the cause of it himself; but cannot, from the nature of the thing, determine whether it is caused by body or spirit, by something near, or by something at a distance. It has no similitude to anything else, so as to admit of a com- parison; and, therefore, he can conclude nothing from it, unless, perhaps, that there must be some unknown cause of it. It is evidently ridiculous to ascribe to it figure, colour, extension, or any other quality of bodies. He cannot give it a place, any more than he cain give a place to melancholy or joy; nor can he conceive it to have any existence, ' but when it is smelled. So that it appears to be a simple and original affection or feeling of the mind, altogether inexplicable and unaccountable. It is, in- deed, impossible that it can be in any body: it is a sen- sation, and a sensation can only be in a sentient thing. The various odours have each their different degrees of strength or weakness. Most of them are agreeable or disagreeable; and frequently those that are agreeable when weak, are disagreeable when stronger. When we compare different smells together, we can perceive very few resemblances or contrarieties, or, indeed, relations of any kind between them. They are all so simple in 92 THE PHILOSOPHY OF REID. |Cn. II. themselves, and so different from each other, that it is hardly possible to divide them into genera and species. Most of the names we give them are particular; as the smell of a rose, of a jessamine, and the like. Yet there are some general names as sweet, stinking, musty, putrid, cadaverous, aromatic. Some of them seem to refresh and animate the mind, others to deaden and depress it. Section III. SENSATION AND REMEMBRANCE, NATURAL PRINCIPLES OF BELIEF. So far we have considered this sensation abstractly. Let us next compare it with other things to which it bears some relation. And first I shall compare this sen- sation with the remembrance, and the imagination of it. I can think of the smell of a rose when I do not smell it; and it is possible that when I think of it, there is neither rose nor smell anywhere existing. But when I smell it, I am necessarily determined to believe that the sen- sation really exists. This is common to all sensations, that, as they cannot exist but in being perceived, so they cannot be perceived but they must exist. I could as easily doubt of my own existence, as of the existence of my sensations. Even those profound philosophers who have endeavoured to disprove their own existence, have yet left their sensations to stand upon their own bottom, stript of a subject, rather than call in question the reali- ty of their existence. Here, then, a sensation, a smell, for instance, may be presented to the mind three different ways: it may be smelled, it may be remembered, it may be imagined or thought of. In the first case, it is necessarily accom- panied with a belief of its present existence; in the sec- ond, it is necessarily accompanied with a belief of its past existence; and in the last, it is not accompanied with be- SEC. HI.] THE PHILOSOPHY OF REID. 93 lief at all,* but is what the logicians call a simple appre- hension. Why sensation should compel our belief of the pres- ent existence of the thing, memory a belief of its past ex- istence, and imagination no belief at all, I believe no philosopher can give a shadow of reason, but that such is the nature of these operations: they are all simple and original, and therefore inexplicable acts of the mind. Suppose that once, and only once, I smelled a tube- rose in a certain room, where it grew in a pot, and gave a very grateful perfume. Next day I relate what I saw and smelled. When I attend as carefully as I can to what passes in my mind in this case, it appears evident that the very thing I saw yesterday, and the fragrance I smelled, are now the immediate objects of my mind, when I remember it. Further, I can imagine this pot and flower transported to the room where I now sit, and yielding the same perfume. Here likewise it appears, that the individual thing which I saw and smelled, is the object of my imagination. Philosophers indeed tell me, that the immediate ob- ject of my memory and imagination- in this case, is not the past sensation, but an idea of it, an image, phan- tasm, or species, f of the odour I smelled: that this idea now exists in my mind, or in my sensorium; and the mind, contemplating this present idea, finds it a repre- sentation of what is past, or of what may exist; and ac- cordingly calls it memory, or imagination. This is the doctrine of the ideal philosophy; which we shall not * This is not strictly correct. The imagination of an object is necessarily accompanied with a belief of the existence of the mental representation. Reid uses the term existence for objective existence only, and takes no account of the possibility of a subjective exist- ence. H. f It will be observed, that Reid understands by Idea, Image, Phantasm, Species, &., always a tertiumquid numerically different both from the Object existing and from the Subject knowing. He had formed no conception of a doctrine in which a representative ob- 94 THE PHILOSOPHY OF REID. [CH. il. now examine, that we may not interrupt the thread of the present investigation. Upon the strictest attention, memory appears to me to have things that are past, and not present ideas, for its object. We shall afterwards examine this system of ideas, and endeavour to make it appear, that no solid proof has ever been advanced of . the existence of ideas; that they are a mere fiction and hypothesis, contrived to solve the phenomena of the human understanding; that they do not at all answer this end; and that this hypothesis of ideas or images of things in the mind, or in the sensorium, is the parent of those many paradoxes so shocking to common sense, and of that scepticism which disgrace our philosophy of the mind, and have brought upon it the ridicule and contempt of sensible men. In the meantime, I beg leave to think, with the vul- gar, that, when I remember the smell of the tuberose, that very sensation which I had yesterday, and which has now no more any existence, is the immediate object of my memory; and when I imagine it present, the sen- sation itself, and not any idea of it, is the object of my imagination. But, though the object of my sensation, memory, and imagination, be in this case the same, yet these acts or operations of the mind are as different, and as easily distinguishable, as smell, taste, and sound. I am conscious of a difference in kind between sensation and memory, and between both and imagination. I find this also, that the sensation compels my belief of the present existence of the smell, and memory my belief of its past existence. There is a smell, is the immediate testimony of sense; there was a smell, is the immediate testimony of memory. If you ask me, why I believe that the smell exists, I can give no other reason, nor ject is allowed, but only as a modification of the mind itself. On the evil consequences of this error, both on his own philosophy and on his criticism of other opinions, H. SEC. IV.] THE PHILOSOPHY OF RElD. 95 shall ever be able to give any other, than that I smell it. If you ask, why I believe that it existed yesterday, I can give no other reason but that I remember it. Sensation and memory, therefore, are simple, original, , and perfectly distinct operations of the mind, and both of them are original principles of belief. Imagination is distinct from both, but is no principle of belief. Sen- sation implies the present existence of its object, mem- ory its past existence, but imagination views its object naked, and without any belief of its existence or non- existence, and is therefore what the schools call Simple Apprehension. * Section IV. JUDGMENT AND BELIEF IN SOME CASES PRE-CEDE SIMPLE AP- PREHENSION. ^ But here, again, the ideal system comes in/ourjwayj_Jt teaches us that the first operation of the mincTabout its ideas, is simple apprehension that is, the bare concep- tion of a thing without any belief about it: and that, after we have got simple apprehensions, by comparing them together, we perceive agreements or disagreements / between them; and that this perception of the agreement/ or disagreement of ideas, is all that we call belief, judg/ ment, or knowledge. Now, this appears to me to be all fiction, without any foundation in nature; for it is acknowledged by all, that sensation must go before memory and imagination; and hence it necessarily fol- x\ \r lows, that apprehension, accompanied with belief and J J^T knowledge, must go before simple apprehension, at least in the matters we are now speaking of. So that here, in- * Simple Apprehension, in the language of the Schools, has no reference to any exclusion of belief. It was merely given to the con- ception of simple, in contrast to the cognition of complex, terms. 96 THE PHILOSOPHY OF REID. [Cn. II. stead of saying that the belief or knowledge is got by put- ting together and comparing the simple apprehensions, we ought rather to say that the simple apprehension is per- formed by resolving and analysing a natural and origi- nal judgment. And it is with the operations of the mind, in this case, as with natural bodies, which are, indeed, compounded of simple principles or elements. Nature does not exhibit these elements separate, to be compounded by us; she exhibits them mixed and compounded in concrete bodies, and it is only by art and chemical analysis that they can be separated. Section V. TWO THEORIES OF THE NATURE OF BELIEF REFUTED CON- CLUSIONS FROM WHAT HATH BEEN SAID. But what is this belief or knowledge which accompa- nies sensation and memory ? Every man knows what it is, but no man can define it. Does any man pretend to define sensation, or to define consciousness ? It is hap- py, indeed, that no man does. And if no philosopher had endeavoured to define and explain belief, some par- adoxes in philosophy, more incredible than ever were brought forth by the most abject superstition or the most frantic enthusiasm, had never seen the light. Of this kind surely is that modern discovery of the ideal philos- ophy, that sensation, memory, belief, and imagination, when they have the same object, are only different de- grees of strength and vivacity in the idea. * Suppose the idea to be that of a future state after death: one man be- lieves it firmly this means no more than that he hath a strong and lively idea of it; another neither believes nor disbelieves that is, he has a weak and faint idea. Sup- pose, now, a third person believes firmly that there is no * He refers to Hume. H. SBC. V.] THE PHILOSOPHY OF REID. 97 such thing, I am at a loss to know whether his idea be faint or lively: if it is faint, then there may be a firm belief where the idea is faint; if the idea is lively, then the be- lief of a future state and the belief of no future state must be one and the same. The same arguments that are used to prove that belief implies only a stronger idea of the object than simple apprehension, might as well be used to prove that love implies only a stronger idea of the object than indifference. And then what shall we say of hatred, which must upon this hypothe- sis be a degree of love, or a degree of indifference ? If it should be said, that in love there is something more than an idea to wit, an affection of the mind may it not be said with equal reason, that in belief there is AJ something more than an idea to wit, an assent or per- suasion of the mind ? But perhaps it may be thought as ridiculous to argue against this strange opinion, as to maintain it. Indeed, if a man should maintain that a circle, a square, and a triangle differ only in magnitude, and not in figure, I believe he would find nobody disposed either to believe him or to argue against him; and yet I do not think it less shocking to common sense, to maintain that sensa- tion, memory, and imagination differ only in degree, and not in kind. I know it is said, that, in a delirium, or in dreaming, men are apt to mistake one for the other. But does it follow from this, that men who are neither dreaming nor in a delirium cannot distinguish them ? But how does a man know that he is not in a delirium ? I cannot tell: neither can I tell how a man knows that he exists. But, if any man seriously doubts whether he is in a delirium, I think it highly probable that he is, and that it is time to seek for a cure, which I am persuaded he will not find in the whole system of logic. I mentioned before Locke's notion of belief or know- ledge ; he holds that it consists in a perception of the 98 THE PHILOSOPHY OF REID. [Cn. II. agreement or disagreement of ideas ; and this he values himself upon as a very important discovery. We shall have occasion afterwards to examine more particularly this grand principle of Locke's philosophy, and to shew that it is one of the main pillars of modern scepticism, although he had no intention to make that use of it. At present let us only consider how it agrees with the instances of belief now under consideration ; and whether it gives any light to them. I believe that the sensation I have exists ; and that the sensation I remember does not now exist, but did exist yesterday. Here, according to Locke's system, I compare the idea of a sensation with the ideas of past and present exist- ence : at one time I perceive that this idea agrees with that of present existence, but disagrees with that of past existence ; but, at another time, it agrees with the idea of past existence, and disagrees with that of present ex- istence. Truly these ideas seem to be very capricious in their agreements and disagreements. Besides, I can- not, for my heart, conceive what is meant by either. I say a sensation exists, and I think I understand clearly what I mean. But you want to make the thing clearer, and for that end tell me, that there is an agreement be- tween the idea of that sensation and the idea of existence. To speak freely, this conveys to me no light, but darkness ; I can conceive no otherwise of it, than as an odd and obscure circumlocution. I conclude, then, ' that the belief which accompanies sensation and mem- ory, is a simple act of the mind, which cannot be de- fined. It is, in this respect, like seeing and hearing, which can never be so defined as to be understood by those who have not these faculties ; and to such as have them, no definition can make these operations more clear than they are already. In like manner, every man that has any belief and he must be a curi- osity that has none knows perfectly what belief is, but can never define or explain it. I conclude, also, that SKC.VI.] THE PHILOSOPHY OF REID. 99 sensation, memory, and imagination, even where they have the same object, are operations of a quite differ- ent nature, and perfectly distinguishable by those who are sound and sober. A man that is in danger of con- founding them, is indeed to be pitied ; but whatever relief he may find from another art, he can find none from logic or metaphysic. I conclude further, that it is no less a part of the human constitution, to believe the present existence of our sensations, and to believe the past existence of what we remember, than it is to believe that twice two make four. The evidence of sense, the evidence of memory, and the evidence of the necessary relations of things, are all distinct and original kinds of evidence, equally grounded on our constitution : none of them depends upon, or can be resolved into another. To reason against any of these kinds of evidence, is absurd; nay, to reason for them is absurd. They are first principles ; and such fall not within the province of reason, * but of common sense. Section VI. APOLOGY FOR METAPHYSICAL ABSURDITIES SENSATION WITH- OUT A SENTIENT, A CONSEQUENCE OF THE THEORY OF IDEAS CONSEQUENCES OF THIS STRANGE OPINION. Having considered the relation which the sensation of smelling bears to the remembrance and imagination of it, I proceed to consider what relation it bears to a mind or sentient principle. It is certain, no man can conceive or believe smelling to exist of itself, without a mind, or something that has the power of smelling, of which it is called a sensation, an operation, or feeling. Yet, if any man should demand a proof, that sensation cannot be without a mind or sentient being, I confess * See note, p. 79. H. 100 . THE PHILOSOPHY OF REID. [Cn. II. that I can give none ; and that to pretend to prove it, seems to me almost as absurd as to deny it. This might have been said without any apology before the "Treatise of Human Nature" appeared in the world. For till that time, no man, as far as I know, ever thought either of calling in question that principle, or of giving a reason for his belief of it. Whether thinking beings were of an ethereal or igneous nature, whether material or immaterial, was variously disputed; but that thinking is an operation of some kind of being or other, was always taken for granted, as a principle that could not possibly admit of doubt. However, since the author above mentioned, who is undoubtedly one of the most acute metaphysicians that this or any age hath produced, hath treated it as a vulgar prejudice, and maintained that the mind is only a suc- cession of ideas and impressions without any subject; his opinion, however contrary to the common appre- hensions of mankind, deserves respect. I beg there- fore, once for all, that no offence may be taken at charg- ing this or other metaphysical notions with absurdity, or with being contrary to the common sense of mankind. No disparagement is meant to the understandings of the authors or maintainers of such opinions. Indeed, they commonly proceed, not from defect of understanding, but from an excess of refinement the reasoning that leads to them often gives new light to the subject, and shews real genius and deep penetration in the author ; and the premises do more than atone for the conclu- sion. If there are certain principles, as I think there are, which the constitution of our nature leads us to believe, and which we are under a necessity to take for granted in the common concerns of life, without being able to give a reason for them these are what we call the prin- ciples of common sense ; and what is manifestly con- trary to them, is what we call absurd. SEC. VI.] THE PHILOSOPHY OF REID. IOI Indeed, if it is true, and to be received as a principle of philosophy, that sensation and thought may be with- out a thinking being, it must be acknowledged to be the most wonderful discovery that this or any other age hath produced. The received doctrine of ideas is the princi- ple from which it is deduced, and of which indeed it seems to be a just and natural consequence. And it is probable, that it would not have been so late a discov- ery, but that it is so shocking and repugnant to the com- mon apprehensions of mankind, that it required an un- common degree of philosophical intrepidity to usher it into the world. It is a fundamental principle of the ideal system, that every object of thought must be an impres- sion or an idea that is, a faint copy of some preceding impression. This is a principle so commonly received, that the author above mentioned, although his whole sys- tem is built upon it, never offers the least proof of it. It is upon this principle, as a fixed point, that he erects his metaphysical engines, to overturn heaven and earth, body and spirit. And, indeed, in my apprehension, it is alto- gether sufficient for the purpose. For, if impressions and ideas are the only objects of thought, then heaven and earth, and body and spirit, and everything you please, must signify only impressions and ideas, or they must be words without any meaning. It seems, there- fore, that this notion, however strange, is closely con- nected with the received doctrine of ideas, and we must either admit the conclusion, or call in question the premises. Ideas seem to have something in their nature un- friendly to other existences. They were first introduced into philosophy, in the humble character of images or representatives of things : and in this character they seemed not only to be inoffensive, but to serve admir- ably well for explaining the operations of the human un- derstanding. But, since men began to reason clearly and distinctly about them, they h rjJoJ lirgrrr" sup- ^5^ OP 102 THE PHILOSOPHY OF REID. [CH.II. planted their constituents, and undermined the existence of everything but themselves. First, they discarded all sec- ondary qualities of bodies ; and it was found out by their means, that fire is not hot, nor snow cold, nor honey sweet ; and, in a word, that heat and cold, sound, colour, taste, and smell, are nothing but ideas or impres- sions. Bishop Berkeley advanced them a step higher, and found out, by just reasoning from the same princi- ples, that extension, solidity, space, figure, and body, are ideas, and that there is nothing in nature but ideas and spirits. But the triumph of ideas was completed by the "Treatise of Human Nature/' which discards spirits also, and leaves ideas and impressions as the sole exist- ences in the universe. What if, at last, having nothing else to contend with, they should fall foul of one another, and leave no existence in nature at all ? This would surely bring philosophy into danger ; for what should we have left to talk or to dispute about ? However, hitherto these philosophers acknowledge the existence of impressions and ideas ; they acknow- ledge certain laws of attraction, or rules of precedence, according to which, ideas and impressions range them- selves in various forms, and succeed one another : but that they should belong to a mind, as its proper goods and chattels, this they have found to be a vulgar error. These ideas are as free and independent as the birds of the air, or as Epicurus's atoms when they pursued their journey in the vast inane. Shall we conceive them like the films of things in the Epicurean system ? Principio hoc dice, rerum simulacra vagari, Multa modis multis, in cunctas undique parteis Tenuia, quae facile inter se junguntur in auris, Obvia cum veniunt LUCR. Or do they rather resemble Aristotle's intelligible species, after they are shot forth from the object, and before they have yet struck upon the passive intellect ? But why SEC. VI.] THE PHILOSOPHY OF REID. 103 should we seek to compare them with anything, since there is nothing in nature but themselves ? They make the whole furniture of the universe ; starting into exist- ence, or out of it, without any cause ; combining into parcels, which the vulgar call minds ; and succeeding one another by fixed laws, without time, place, or author of those laws. Yet, after all, these self-existent and independent ideas look pitifully naked and destitute, when left thus alone in the universe, and seem, upon the whole, to be in a worse condition than they were before. Des Cartes, Malebranche, and Locke, as they made much use of ideas, treated them handsomely, and provided them in decent accommodation ; lodging them either in the pineal gland, or in the pure intellect, or even in the divine mind. They moreover clothed them with a commission, and made them representatives of things, which gave them some dignity and character. But the "Treatise of Hu- man Nature," though no less indebted to them, seems to have made but a bad return, by bestowing upon them this independent existence : since thereby they are turned out of house and home, and set adrift in the world, without friend or connection, without a rag to cover their nakedness ; and who knows but the whole system of ideas may perish by the indiscreet zeal of their friends to exalt them ? However this may be, it is certainly a most amazing discovery that thought and ideas may be without any thinking being a discovery big with consequences which cannot easily be traced by those deluded mortals who think and reason in the common track. We were always apt to imagine, that thought supposed a thinker, and love a lover, and treason a traitor : but this, it seems, was all a mistake ; and it is found out, that there may be treason without a traitor, and love without a lover, laws without a legislator, and punishment without a suf- ferer, succession without time, and motion without any- 104 THE PHILOSOPHY OF REID, |CH. II. thing moved, or space in which it may move : or if, in these cases, ideas are the lover, the sufferer, the traitor, it were to be wished that the author of this discovery had farther condescended to acquaint us whether ideas can converse together, and be under obligations of duty or gratitude to each other ; whether they can make promises and enter into leagues and covenants, and ful- fil or break them, and be punished for the breach. If one set of ideas makes a covenant, another breaks it, and a third is punished for it, there is reason to think that justice is no natural virtue in this system. It seemed very natural to think, that the ' ' Treatise of Human Nature" required an author, and a very ingenious one too; but now we learn that it is only a set of ideas which came together and arranged them- selves by certain associations and attractions. After all, this curious system appears not to be fitted to the present state of human nature. How far it may suit some choice spirits, who are refined from the dregs of common sense, I cannot say. It is acknowledged, I think, that even these can enter into this system only in their most speculative hours, when they soar so high in pursuit of those self-existent ideas as to lose sight of all other things. But when they condescend to mingle again with the human race, and to converse with a friend, a companion, or a fellow-citizen, the ideal sys- tem vanishes; common sense, like an irresistible torrent, carries them along; and, in spite of all their reasoning and philosophy, they believe their own existence, and the existence of other things. Indeed, it is happy they do so; for, if they should carry their closet belief into the world, the rest of man- kind would consider them as diseased, and send them to an infirmary. Therefore, as Plato required certain pre- vious qualifications of those who entered his school, I think it would be prudent for the doctors of this ideal philosophy to do the same, and to refuse admittance to SEC. VII.] THE PHILOSOPHY OF REID. 105 every man who is so weak as to imagine that he ought to have the same belief in solitude and in company, or that his principles ought to have any influence upon his practice ; for this philosophy is like a hobby-horse, which a man in bad health may ride in his closet, with- out hurting his reputation; but, if he should take him abroad with him to church, or to the exchange, or to the play-house, his heir would immediately call a jury, and seize his estate. Section VIL THE CONCEPTION AND BELIEF OF A SENTIENT BEING OR MIND IS SUGGESTED BY OUR CONSTITUTION THE NOTION OF RE- LATIONS NOT ALWAYS GOT BY COMPARING THE RELATED IDEAS. Leaving this philosophy, therefore, to those who have occasion for it, and can use it discreetly as a chamber exercise, we may still inquire how the rest of mankind, and even the adepts themselves, except in some solitary moments, have got so strong and irresistible a belief, that thought must have a subject, and be the act of some thinking being; how every man believes himself to be something distinct from his ideas and impressions some- thing which continues the same identical self when all. his ideas and impressions are changed. It is impossible to trace the origin of this opinion in history; for all lan- guages have it interwoven in their original construction. All nations have always believed it. The constitution of all laws and governments, as well as the common transactions of life, suppose it. It is no less impossible for any man to recollect when he himself came by this notion; for, as far back as we can remember, we were already in possession of it, and as fully persuaded of our own existence, and the exist- ence of other things, as that one and one make two. It seems, therefore, that this opinion preceded all reasoning, 106 THE PHILOSOPHY OF REID. [Cn.ll. and experience, and instruction; and this is the more probable, because we could not get it by any of these means. It appears, then, to be an undeniable fact, that, from thought or sensation, all mankind, constantly and invariably, from the first dawning of reflection, do infer a power or faculty of thinking and a permanent being or mind to which that faculty belongs; and that we as invariably ascribe all the various kinds of sensation and thought we are conscious of, to one individual mind or self. But by what rules of logic we make these inferences, it is impossible to shew; nay, it is impossible to shew how our sensations and thoughts can give us the very notion and conception either of a mind or of a faculty. The faculty of smelling is something very different from the actual sensation of smelling; for the faculty may re- main when we have no sensation. And the mind is no -, less different from the faculty; for it continues the same individual being when that faculty is lost. Yet this sen- sation suggests to us both a faculty and a mind; and not only suggests the notion of them, but creates a belief of their existence; although it is impossible to discover, by reason, any tie or connection between one and the other. What shall we say, then ? Either those inferences which we draw from our sensations namely, the exist- ence of a mind, and of powers or faculties belonging to it are prejudices of philosophy or education, mere fic- tions of the mind, which a wise man should throw off as he does the belief of fairies; or they are judgments of nature judgments not got by comparing ideas, and per- ceiving agreements and disagreements, but immediately inspired by our constitution^ If this last is the case, as I apprehend it is, it will be impossible to shake off those opinions, and we must yield to them at last, though we struggle hard to get rid of them. And if we could, by a determined obstinacy, SEC. VII.] THE PHILOSOPHY OF REID. IO7 shake off the principles oF our nature, this is not to act the philosopher, but the fool or the madman. It is in> cumbent upon those who think that these are not natural principles, to shew, in the first place, how we can otherwise get the notion of a mind and its faculties; and then to shew how we come to deceive ourselves into the opinion that sensation cannot be without a sentient being. It is the received doctrine of philosophers, that our notions of relations can only be got by comparing the related ideas: but, in the present case, there seems to be an instance to the contrary. It is not by having first the notions of mind and sensation, and then comparing them together, that we perceive the one to have the rela- tion of a subject or substratum, and the other that of an act or operation: on the contrary, one of the related things to wit, sensation suggests to us both the cor- relate and the relation. I beg leave to make use of the word suggestion, be- cause I know not one more proper, to express a power of the mind, which seems entirely to have escaped the notice of philosophers, and to which we owe many of our simple notions which are neither impressions nor ideas, as well as many original principles of belief. I shall endeavor to illustrate, by an example, what I understand by this word. We all know, that a certain kind of sound suggests immediately to the mind, a coach passing in the street; and not only produces the imagination, but the belief, that a coach is passing. Yet there is here no comparing of ideas, no perception of agreements or disagreements, to produce this belief: nor is there the least similitude between the sound we hear and the coach we imagine and believe to be passing.* * "The word suggest " (says Mr. Stewart, in reference to the pre- ceding passage) "is much used by Berkeley, in this appropriate and technical sense, not only in his ' Theory of Vision, ' but in his * Prin- 108 THE PHILOSOPHY OF REID. [Cn. II. It is true that this suggestion is not natural and original; if is the result of experience and habit. But I think it appears, from what hath been said, that there are natural suggestions: particularly, that sensation suggests the no- tion of present existence, and the belief that what we perceive or feel does now exist; that memory suggests the notion of past existence, and the belief that what we remember did exist in time past; and that our sensations and thoughts do also suggest the notion of a mind, and the belief of its existence, and of its relation to our ciples of Human Knowledge,' and in his ' Minute Philosopher.' It expresses, indeed, the cardinal principle on which his ' Theory of Vision ' hinges, and is now so incorporated with some of our best metaphysical speculations, that one cannot easily conceive how the use of it was so long dispensed with. Locke uses the word excite for the same purpose; but it seems to imply an hypothesis concerning the mechanism of the mind, and by no means expresses the fact in question with the same force and precision. "It is remarkable, that Dr. Reid should have thought it incum- bent on him to apologise for introducing into philosophy a word so familiar to every person conversant with Berkeley's works. I beg leave to make use of the word suggestion, because, ' &c " So far Dr. Reid's use of the word coincides exactly with that of Berkeley ; but the former will be found to annex to it a meaning more extensive than the latter, by employing it to comprehend, not only those intimations which are the result of experience and habit; but another class of intimations, (quite overlooked by Berkeley,) those which result from the original frame of the human mind." Dissertation on the History of Metaphysical and Ethical Science. P. 167. Second edition. Mr. Stewart might have adduced, perhaps, a higher and, certainly, a more proximate authority, in favour, not merely of the term in general, but of Reid's restricted employment of it, as an intimation of what he and others have designated the Common Sense of man- kind. The following sentence of Tertullian contains a singular an- ticipation, both of the philosophy and of the philosophical phrase- ology of our author. Speaking of the universal belief of the soul's immortality: " Natura pleraque suggeruntur, quasi de flttblico sensu quo animam Deus ditare dignatus est." DE ANIMA, c. 2. Some strictures on Reid's employment of the term suggestion may be seen in the " Versuche" of Tetens, I., p. 508, sqq. H. SEC. VIII.] THE PHILOSOPHY OF REID. 109 thoughts. By a like natural principle it is, that a be- ginning of existence, or any change in nature, suggests to us the notion of a cause, and compels our belief of its existence. And, in like manner, as shall be shewn when we come to the sense of touch, certain sensations of touch, by the constitution of our nature, suggest to us extension, solidity, and motion, which are nowise like to sensations, although they have been hitherto con- founded with them. Section VIII. THERE IS A QUALITY OR VIRTUE IN BODIES, WHICH WE CALL THEIR SMELL HOW THIS IS CONNECTED IN THE IMAGINA- TION WITH THE SENSATION. We have considered smell as signifying a sensation, feeling, or impression upon the mind; and in this sense, it can only be in a mind, or sentient being: but it is evi- dent that mankind gives the name of smell much more frequently to something which they conceive to be ex- ternal, and to be a quality of body: they understand something by it which does not at all infer a mind; and have not the least difficulty in conceiving the air per- fumed with aromatic odours in the deserts of Arabia, or in some uninhabited island, where the human foot never trod. Every sensible day-labourer hath as clear a notion of this, and as full a conviction of the possibility of it, as he hath of his own existence; and can no more doubt of the one than of the other. Suppose that such a man meets with a modern phi- losopher, and wants to be informed what smell in plants is. The philosopher tells him, that there is no smell in plants, nor in anything but in the mind; that it is impossible there can be smell but in a mind; and that all this hath been demonstrated by modern philosophy. The plain man will, no doubt, be apt to think him merry: but, if he finds that he is serious, his next conclu- IIO THE PHILOSOPHY OF REID. [CH. ll. sion will be that he is mad; or that philosophy, like magic, puts men into a new world, and gives them different faculties from common men. And thus philoso- phy and common sense are set at variance. But who is to blame for it ? In my opinion the philosopher is to blame. For if he means by smell, what the rest of man- kind most commonly mean, he is certainly mad. But if he puts a different meaning upon the word, without ob- serving it himself, or giving warning to others, he abuses language and disgraces philosophy, without doing any service to truth: as if a man should exchange the mean- ing of the words daughter and cow, and then endeavour to prove to his plain neighbour, that his cow is his daughter, and his daughter his cow. I believe there is not much more wisdom in many of those paradoxes of the ideal philosophy, which to plain sensible men appear to be palpable absurdities, but with the adepts pass for profound discoveries. I resolve, for my own part, always to pay a great regard to the dictates of common sense, and not to depart from them without absolute necessity: and, therefore, I am apt to think that there is really something in the rose or lily, which is by the vulgar called smell, and which continues to exist when it is not smelled: and shall proceed to inquire what this is; how we come by the notion of it; and what rela- tion this quality or virtue of smdl hath to the sensation which we have been obliged to call by the same name, for want of another. Let us therefore suppose, as before, a person begin- ning to exercise the sense of smelling; a little experience will discover to him that the nose is the organ of this sense, and that the air, or something in the air, is a medium of it. And finding, by farther experience, that, v when a rose is near, he has a certain sensation, when it is removed, the sensation is gone, he finds a connection in nature betwixt the rose and this sensation. The rose is considered as a cause, occasion, or antecedent of the SEC. IX.] THE PHILOSOPHY OF REID. Ill sensation; the sensation as an effect or consequence of the presence of the rose; they are associated in the mind, and constantly found conjoined in the imagination. But here it deserves our notice, that, although the sen- sation may seem more closely related to the mind its subject, or to the nose its organ, yet neither of these con- nections operate so powerfully upon the imagination as its connection with the rose its concomitant. The reason of this seems to be, that its connection with the mind is more general, and noway distinguisheth it from other smells, or even from tastes, sounds, and other kinds of sensations. The relation it hath to the organ is likewise general, and doth not distinguish it from other smells; but the connection it hath with the rose is special and constant; by which means they become almost insepa- rable in the imagination, in like manner as thunder and lightning, freezing and cold. Section IX. THAT THERE IS A PRINCIPLE IN HUMAN NATURE, FROM WHICH THE NOTION OF THIS, AS WELL AS ALL OTHER NATURAL VIRTUES OR CAUSES, IS DERIVED. In order to illustrate further how we come to conceive a quality or virtue in the rose which we call smell, and what this smell is, it is proper to observe, that the mind begins very early to thirst after principles which may direct it in the exertion of its powers. The smell of a rose is a certain affection or feeling of the mind; and, as it is not constant, but comes and goes, we want to know when and where we may expect it; and are uneasy till we find something which, being present, brings this feeling along with it, and, being removed, removes it. This, when found, we call the cause of it; not in a strict and philosophical sense, as if the feeling were really effected or produced by that cause, but in a popu- 112 THE PHILOSOPHY OF REID. [Cn. II. lar sense; for the mind is satisfied if there is a constant conjunction between them; and such causes are in reality nothing else but laws of nature. Having found the smell thus constantly conjoined with the rose, the mind is at rest, without inquiring whether this conjunction is owing to a real efficiency or not; that being a philosophical inquiry, which does not concern human life. But every discovery of such a constant conjunction is of real im- portance in life, and makes a strong impression upon the mind. So ardently do we desire to find everything that hap- pens within our observation thus connected with some- thing else as its cause or occasion, that we are apt to fancy connections upon the slightest grounds; and this weakness is most remarkable in the ignorant, who know least of the real connections established in nature. A man meets with an unlucky accident on a certain day of the year, and, knowing no other cause of his misfortune, he is apt to conceive something unlucky in that day of the calendar; and, if he finds the same connection hold a second time, is strongly confirmed in his superstition. I remember, many years ago, a white ox was brought into this country, of so enormous a size that people came many miles to see him. There happened, some months after, an uncommon fatality among women in child-bear- ing. Two such uncommon events, following one an- other, gave a suspicion of their connection, and oc- casioned a common opinion among the country-people that the white ox was the cause of this fatality. However silly and ridiculous this opinion was, it sprung from the same root in human nature on which all natural philosophy grows namely, an eager desire to find out connections in things, and a natural, original, and unaccountable propensity to believe that the con- nections which we have observed in time past will continue in time to come. Omens, portents, good and bad luck, palmistry, astrology, all the numerous arts of SEC. IX.] THE PHILOSOPHY OF REID. 113 divination and of interpreting dreams, false hypotheses and systems, and true principles in the philosophy of nature, are all built upon the same foundation in the human constitution, and are distinguished only accord- ing as we conclude rashly from too few instances, or cautiously from a sufficient induction. As it is experience only that discovers these connec- tions between natural causes and their effects; without inquiring further, we attribute to the cause some vague and indistinct notion of power or virtue to produce the effect. And, in many cases, the purposes of life do not make it necessary to give distinct names to the cause and the effect. Whence it happens, that, being closely connected in the imagination, although very unlike to each other, one name serves for both; and, in common discourse, is most frequently applied to that which, of the two, is most the object of our attention. This occa- sions an ambiguity in many words, which, having the same causes in all languages, is common to all, and is apt to be overlooked even by philosophers. Some instances will serve both to illustrate and confirm what we have said. Magnetism signifies both the tendency of the iron to- wards the magnet, and the power of the magnet to pro- duce that tendency; and, if it was asked, whether it is a quality of the iron or of the magnet, one would perhaps be puzzled at first; but a little attention would discover, that we conceive a power or virtue in the magnet as the cause, and a motion in the iron as the effect; and, although these are things quite unlike, they are so united in the imagination, that we give the common name of magnetism to both. The same thing may be said of gravitation, which sometimes signifies the tendency of bodies towards the earth, sometimes the attractive power of the earth, which we conceive as the cause of that ten- dency. We may observe the same ambiguity in some of Sir Isaac Newton's definitions; and that even in words 114 THE PHILOSOPHY OF REID. [Cn. II. of his own making. In three of his definitions, he ex- plains very distinctly what he understands by the absolute quantity, what by the accelerative quantity, and what by the motive quantity, of a centripetal force. In the first of these three definitions, centripetal force is put for the cause, which we conceive to be some power or virtue in the centre or central body; in the two last, the same word is put for the effect of this cause, in producing velocity, or in producing motion towards that centre. Heat signifies a sensation, and cold a contrary one; but heat likewise signifies a quality or state of bodies, which hath no contrary, but different degrees. When a man feels the same water hot to one hand and cold to the other, this gives him occasion to distinguish between the feeling and the heat of the body; and, although he knows that the sensations are contrary, he does not imagine that the body can have contrary qualities at the same time. And when he finds a different taste in the same body in sickness and in health, he is easily con- vinced, that the quality in the body called taste is the same as before, although the sensations he has from it are perhaps opposite. The vulgar are commonly charged by philosophers, with the absurdity of imagining the smell in the rose to be something like to the sensation of smelling; but I think unjustly; for they neither give the same epithets to both, nor do they reason in the same manner from them. What is smell in the rose ? It is a quality or vir- tue of the rose, or of something proceeding from it, which we perceive by the sense of smelling; and this is all we know of the matter. But what is smelling ? It is an act of the mind, but is never imagined to be a qual- ity of the mind. Again, the sensation of smelling is con- ceived to infer necessarily a mind or sentient being; but smell in the rose infers no such thing. We say, this body smells sweet, that stinks; but we do not say, this mind smells, sweet and that stinks. Therefore, smell in SEC. IX] THE PHILOSOPHY OF REID. 115 the rose, and the sensation which it causes, are not con- ceived, even by the vulgar, to be things of the same kind, although they have the same name. From what hath been said, we may learn that the smell of a rose signifies two things: First, a sensation, which can have no existence but when it is perceived, and can only be in a sentient being or mind; Secondly, it signifies some power, quality, or virtue, in the rose, or in effluvia proceeding from it, which hath a permanent existence, independent of the mind, and which, by the constitution of nature, produces the sensation in us. By the original constitution of our nature, we are both led to believe that there is a permanent cause of the sensa- tion, and prompted to seek after it; and experience de- termines us to place it in the rose. The names of all smells, tastes, sounds, as well as heat and cold, have a like ambiguity in all languages; but it deserves our at- tention, that these names are but rarely, in common lan- guage, used to signify the sensations; for the most part, they signify the external qualities which are indicated by the sensations the cause of which phenomenon I take to be this. Our sensations have very different degrees of strength. Some of them are so quick and lively as to give us a great deal either of pleasure or of uneasiness. When this is the case, we are compelled to attend to the sensation itself, and to make it an object of thoughf and discourse; we give it a name, which signifies nothing but the sensation; and in this case we readily acknowledge, that the thing meant by that name is in the mind only, and not in anything external. Such are the various kinds of pain, sickness, and the sensations of hunger and other appetites. But, where the sensation is not so interesting as to require to be made an object of thought, our con- stitution leads us to consider it as a sign of something external, which hath a constant conjunction with it; and, having found what it indicates, we give a name to that: the sensation, having no proper name, falls in as an ac- Il6 THE PHILOSOPHY OF REID. [Cn. II. cessory to the thing signified by it, and is confounded under the same name. So that the name may, indeed, be applied to the sensation, but most properly and com- monly is applied to the thing indicated by that sensation. The sensations of smell, taste, sound, and colour, are of infinitely more importance as signs or indications, than they are upon their own account; like the words of a language, wherein we do not attend to the sound but to the sense. Section X. WHETHER IN SENSATION THE MIND IS ACTIVE OR PASSIVE ? There is one inquiry remains, Whether, in smelling, and in other sensations, the mind is active or passive ? This possibly may seem to be a question about words, or, at least, of very small importance; however, if it leads us to attend more accurately to the operations of our minds than we are accustomed to do, it is, upon that very account, not altogether unprofitable. I think the opinion of modern philosophers is, that in sensation the mind is altogether passive.* And this undoubtedly is so far true, that we cannot raise any sensation in our minds by willing it; and, on the other hand, it seems hardly possible to avoid having the sensation when the object is presented. Yet it seems likewise to be true, that, in proportion as the attention is more or less turned to a sensation or diverted from it, that sensation is more or less perceived and remembered. Every one knows that very intense pain may be diverted by a surprise, or by anything that entirely occupies the mind. When we are engaged in earnest conversation, the clock may strike by us without being heard; at least, we remember not, the next moment, that we did hear it. The noise and tumult of a great trading city is not heard by them who have lived in it all their days; but it stuns those \ strangers who have lived in the peaceful retirement of the * This is far too absolutely stated H, SEC. X.] THE PHILOSOPHY OF REID. 117 country. Whether, therefore, there can be any sensation where the mind is purely passive, I will not say; but I think we are conscious of having given some attention to every sensation which we remember, though ever so recent No doubt, where the impulse is strong and uncom- mon, it is as difficult to withhold attention as it is to forbear crying out in racking pain, or starting in a sud- den fright. But how far both might be attained by v strong resolution and practice, is not easy to determine. So that, although the Peripatetics had no good reason to suppose an active and a passive intellect, since attention may be well enough accounted an act of the will, yet I think they came nearer to the truth, in holding the mind \ to be in sensation partly passive and partly active, than the moderns in affirming it to be purely passive. Sensa- tion, imagination, memory and judgment, have, by the vulgar in all ages, been considered as acts of the mind. \ The manner in which they are expressed in all languages, shews this. When the mind is much employed in them, we say it is very active; whereas, if they were impressions only, as the ideal philosophy would lead us to conceive, we ought, in such a case, rather to say, that the mind is very passive; for, I suppose, no man would attribute great activity to the paper I write upon, because it re- ceives variety of characters. The relation which the sensation of smell bears to the memory and imagination of it, and to a mind or subject, is common to all our sensations, and, indeed, to all the operations of the mind: the relation it bears to the will is common to it with all the powers of understanding: and the relation it bears to that quality or virtue of bodies which it indicates, is common to it with the sen- sations of taste, hearing, colour, heat, and cold so that what hath been said of this sense, may easily be applied to several of our senses, and to other operations of the mind; and this, I hope, will apologize for our insisting so long upon it. Il8 THE PHILOSOPHY OF REID. [Cu. III. CHAPTER III. OF TASTING. A GREAT part of what hath been said of the sense of smelling, is so easily applied to those of tasting and hearing, that we shall leave the application entirely to the reader's judgment, and save ourselves the trouble of a tedious repetition. It is probable that everything that affects the taste is, in some degree, soluble in the saliva. It is not con- ceivable how any thing should enter readily, and of its own accord, as it were, into the pores of the tongue, palate, and fauces, unless it had some chemical affinity to that liquor with which these pores are always replete. It is, therefore, an admirable contrivance of nature, that \^ the organs of taste should always be moist with a liquor which is so universal a menstruum, and which deserves to be examined more than it hath been hitherto, both in v that capacity, and as a medical unguent. Nature teaches dogs, and other animals, to use it in this last way; and its subserviency both to taste and digestion shews its efficacy in the former. It is with manifest design and propriety, that the or- gan of this sense guards the entrance of the alimentary canal, as that of smell the entrance of the canal for respiration. And from these organs being placed in such manner that everything that enters into the stomach must undergo the scrutiny of both senses, it is plain that they were intended by nature to distinguish wholesome food from that which is noxious. The brutes have no ^ other means of choosing their food; nor would mankind, in the savage state. And it is very probable that the smell and taste, noway vitiated by luxury or bad habits, CH. III.] THE PHILOSOPHY OF REID. 119 would rarely, if ever, lead us to a wrong choice of food among the productions of nature; although the artificial compositions of a refined and luxurious cookery, or of chemistry and pharmacy, may often impose upon both, and produce things agreeable to the taste and smell, which are noxious to health. And it is probable that both smell and taste are vitiated, and rendered less fit to perform their natural offices, by the unnatural kind of life men commonly lead in society. These senses are likewise of great use to distinguish bodies that cannot be distinguished by our other senses, and to discern the changes which the same body under- goes, which, in many cases, are sooner perceived by taste and smell than by any other means. How many things are there in the market, the eating-house, and the tavern, as well as in the apothecary and chemist's shops, which are known to be what they are ^given out to be, and are perceived to be good or bad in their kind, only by taste or smell ? And how far our judgment of things, by means of our senses, might be improved by accurate attention to the small differences of taste and smell, and other sensible qualities, is not easy to determine. Sir Isaac Newton, by a noble effort of his great genius, at- tempted, from the colour of opaque bodies, to discover the magnitude of the minute pellucid parts of which they are compounded: and who knows what new lights nat- ural philosophy may yet receive from other secondary qualities duly examined ? Some tastes and smells stimulate the nerves and raise the spirits: but such an artificial elevation of the spirits is, by the laws of nature, followed by a depression, which can only be relieved by time, or by the repeated use of the like stimulus. By the use of such things we create an appetite for them, which very much resembles, and hath all the force of a natural one. It is in this manner that men acquire an appetite for snuff, tobacco, strong liquors, laudanum, and the like. 120 THE PHILOSOPHY OF REID. [Cn. III. Nature, indeed, seems studiously to have set bounds to the pleasures and pains we have by these two senses, and to have confined them within very narrow limits, that we might not place any part of our happiness in them; there being hardly any smell or taste so disagree- able that use will not make it tolerable, and at last per- haps agreeable, nor any so agreeable as not to lose its relish by constant use. Neither is there any pleasure or pain of these senses which is not introduced or followed by some degree of its contrary, which nearly balances it; so that we may here apply the beautiful allegory of the divine Socrates that, although pleasure and pain are contrary in their nature, and their faces look different ways, yet Jupiter hath tied them so together that he that lays hold of the one draws the other along with it As there is a great variety of smells, seemingly simple and uncompounded, not only altogether unlike, but some of them contrary to others, and as the same thing may be said of tastes, it would seem that one taste is not less different from another than it is from a smell : and therefore it may be a question, how all smells come to be considered as one genus, and all tastes as another ? What is the generical distinction ? Is it only that the nose is the organ of the one and the pal- ate of the other ? or, abstracting from the organ, is there not in the sensations themselves something common to smells, and something else common to tastes, whereby the one is distinguished from the other? It seems most probable that the latter is the case; and that, under the appearance of the greatest simplicity, there is still in these sensations something of composition. If one considers the matter abstractly, it would seem that a number of sensations, or, indeed, of any other individual things, which are perfectly simple and uncom- pounded, are incapable of being reduced into genera and species; because individuals which belong to a species must have something peculiar to each, by which they CH. III.] THE PHILOSOPHY OF REID. 121 are distinguished, and something common to the whole species. And the same may be said of species which be- long to one genus. And, whether this does not imply some kind of composition, we shall leave to -metaphy- sicians to determine. The sensations both of smell and taste do undoubtedly admit of an immense variety of modifications, which no language can express. If a man was to examine five hundred different wines, he would hardly find two of them that had precisely the same taste. The same thing holds in cheese, and in many other things. Yet, of five hundred different tastes in cheese or wine, we can hardly describe twenty, so as to give a distinct notion of them to one who had not tasted them. Dr. Nehemiah Grew, a most judicious and laborious naturalist, in a discourse read before the Royal Society, anno 1675, ^ atn endeavoured to shew that there are at least sixteen different simple tastes, which he enumerates. How many compounded ones may be made out of all the various combinations of two, three, four, or more of these simple ones, they who are acquainted with the theory of combinations will easily perceive. All these have various degrees of intenseness and weakness. Many of them have other varieties; in some the taste is more quickly perceived upon the application of the sapid body, in others more slowly in some the sensation is more permanent, in others more transient in some it seems to undulate or return after certain intervals, in others it is constant: the various parts of the organ as the lips, the tip of the tongue, the root of the tongue, the fauces, the uvula, and the throat are some of them chiefly affected by one sapid body, and others by an- other. All these, and other varieties of tastes, that ac- curate writer illustrates by a number of examples. Nor is it to be doubted, but smells, if examined with the same accuracy, would appear to have as great variety. 122 THE PHILOSOPHY OF REID. [CH. IV. CHAPTER IV. OF HEARING. Section Z VARIETY OF SOUNDS THEIR PLACE AND DISTANCE LEARNED BY CUSTOM, WITHOUT REASONING. SOUNDS have probably no less variety of modifications, than either tastes or odours. For, first, sounds differ in tone. The ear is capable of perceiving four or five hun- dred variations of tone in sound, and probably as many different degrees of strength; by combining these, we have above twenty thousand simple sounds that differ either in tone or strength, supposing every tone to be perfect. But it is to be observed, that to make a perfect tone, a great many undulations of elastic air are required, which must all be of equal duration and extent, and fol- low one another with perfect regularity; and each undu- lation must be made up of the advance and recoil of in- numerable particles of elastic air, whose motions are all uniform in direction, force, and time. Hence we may easily conceive a prodigious variety in the same tone, arising from irregularities of it, occasioned by the con- stitution, figure, situation, or manner of striking the sono- rous body; from the constitution Of the elastic medium, or its being disturbed by other motions; and from the constitution of the ear itself, upon which the impres- sion is made. A flute, a violin, a hautboy, and a French horn, may all sound the same tone and be easily distinguishable. Nay, if twenty human voices sound the same note, and with equal strength, there will still be some difference. SEC. I.] THE PHILOSOPHY OF REID. l3 The same voice, while it retains its proper distinctions, may yet be varied many ways, by sickness or health, youth or age, leanness or fatness, good or bad humour. The same words spoken by foreigners and natives nay, by persons of different provinces of the same nation may be distinguished. Such an immense variety of sensations of smell, taste, and sound, surely was not given us in vain. They are signs by which we know and distinguish things without us; and it was fit that the variety of the signs should, in some degree, correspond with the variety of the things signified by them. It seems to be by custom that we learn to distinguish both the place of things, and their nature, by means of their sound. That such a noise is in the street, such another in the room above me; that this is a knock at my door, that a person walking up stairs is probably learnt by experience. I remember, that once lying abed, and having been put into a fright, I heard my own heart beat; but I took it to be one knocking at the door, and arose and opened the door oftener than once, before I discovered that the sound was in my own breast. It is probable, that, previous to all experience, we should as little know whether a sound came from the right or left, from above or below, from a great or a small distance, as we should know whether it was the sound of a drum, or a bell, or a cart. Nature is frugal in her operations, and will not be at the expense of a particular instinct, to give us that knowledge which experience will soon produce, by means of a general principle of human nature. For a little experience, by the constitution of human nature, ties together, not only in our imagination, but in our belief, those things which were in their nature un- connected. When I hear a certain sound, I conclude immediately, without reasoning, that a coach passes by. There are no premises from which this conclusion is in- 124 THE PHILOSOPHY OF REID. [Cn. IV. ferred by any rules of logic. It is the effect of a princi- ple of our nature, common to us with the brutes. Although it is by hearing that we are capable of the perceptions of harmony and melody, and of all the charms of music, yet it would seem that these require a higher faculty, which we call a musical ear. This seems to be in very different degrees, in those who have the bare fac- ulty of hearing equally perfect; and, therefore, ought not to be classed with the external senses, but in a higher order. Section II. OF NATURAL LANGUAGE. One of the noblest purposes of sound undoubtedly is language, without which mankind would hardly be able to attain any degree of improvement above the brutes. Language is commonly considered as purely an inven- tion of men, who by nature are no less mute than the brutes; but, having a superior degree of invention and reason, have been able to contrive artificial signs of their thoughts and purposes, and to establish them by com- mon consent. But the origin of language deserves to be more carefully inquired into, not only as this inquiry may be of importance for the improvement of language, but as it is related to the present subject, and tends to lay open some of the first principles of human nature. I shall, therefore, offer some thoughts upon this sub- ject. By language I understand all those signs which man- kind use in order to communicate to others their thoughts and intentions, their purposes and desires. And such signs may be conceived to be of two kinds: First, such as have no meaning but what is affixed to them by compact or agreement among those who use them these are artificial signs; Secondly, such as, previ- ous to all compact or agreement, have a meaning which SEC. II.] THE PHILOSOPHY OF REID. 125 every man understands by the principles of his nature. Language, so far as it consists of artificial signs, may be called artificial; so far as it consists of natural signs, I call it natural. Having premised these definitions, I think it is de- monstrable, that, if mankind had not a natural lan- guage they could never have invented an artificial one by their reason and ingenuity. For all artificial language supposes some compact or agreement to affix a certain meaning to certain signs; therefore, there must be com- pacts or agreements before the use of artificial signs; but there can be no compact or agreement without signs, nor without language; and, therefore, there must be a natu- / ral language before any artificial language can be in- vented: which was to be demonstrated. Had language in general been a human invention, as much as writing or printing, we should find whole na- tions as mute as the brutes. Indeed, even the brutes have some natural signs by which they express their own thoughts, affections, and desires, and understand those of others. A chick, as soon as hatched, understands the different sounds whereby its dam calls it to food, or gives the alarm of danger. A dog or a horse under- stands, by nature, when the human voice caresses, and when it threatens him. But brutes, as far as we know, have no notion of contracts or covenants, or of moral obligation to perform them. If nature had given them these notions, she would probably have given them nat- ural signs to express them. And where nature has de- nied these notions, it is as impossible to acquire them by art, as it is for a blind man to acquire the notion of col- ours. Some brutes are sensible of honour or disgrace; they have resentment and gratitude; but none of them, as far as we know, can make a promise or plight their faith, having no such notions from their constitution. And if mankind had not these notions by nature, and natural signs to express them by, with all their wit 126 THE PHILOSOPHY OF REID. [Cn. IV. and ingenuity they could never have invented lan- guage. The elements of this natural language of mankind, or the signs that are naturally expressive of our thoughts, may, I think, be reduced to these three kinds: modula- tions of the voice, gestures, and features. By means of these, two savages who have no common artificial lan- guage, can converse together, can communicate their thoughts in some tolerable manner; can ask and refuse, affirm and deny, threaten and supplicate; can traffic, enter into covenants, and plight their faith. This might be confirmed by historical facts of undoubted credit, if it were necessary. Mankind having thus a common language by nature, though a scanty one, adapted only to the necessities of nature, there is no great ingenuity required in improving it by the addition of artificial signs, to supply the deficiency of the natural. These artificial signs must multiply with the arts of life, and the improvements of knowledge. The articulations of the voice seem to be, of all signs, the most proper for artificial language; and as mankind have universally used them for that purpose, we may reason- ably judge that nature intended them for it.' But nature probably does not intend that we should lay aside the use of the natural signs; it is enough that we supply their defects by artificial ones. A man that rides always in a chariot, by degrees loses the use of his legs; and one who uses artificial signs only, loses both the knowledge and use of the natural. Dumb people retain much more of the natural language than others, because necessity obliges them to use it. And for the same reason, sav- ages have much more of it than civilized nations. It is by natural signs chiefly that we give force and energy to language; and the less language has of them, it is the less expressive and persuasive. Thus, writing is less ex- pressive than reading, and reading less expressive than speaking without book ;, speaking without the SEC. II.] THE PHILOSOPHY OF REID. 127 proper and natural modulations, force, and variations of the voice, is a frigid and dead language, compared with that which is attended with them; it is still more express- ive when we add the language of the eyes and features; and is then only in its perfect and natural state, and at- tended with its proper energy, when to all these we superadd the force of action. Where speech is natural, it will be an exercise, not of the voice and lungs only, but of all the muscles of the body; like that of dumb people and savages, whose lan- guage, as it has more of nature, is more expressive, and is more easily learned. Is it not pity that the refinements of a civilized life, in- stead of supplying the defects of natural language, should root it out and plant in its stead dull and lifeless articu- lations of unmeaning sounds, or the scrawling of insig- nificant characters ? The perfection of language is com- monly thought to be, to express human thoughts and sentiments distinctly by these dull signs; but if this is the perfection of artificial language, it is surely the. cor- ruption of the natural. Artificial signs signify, but they do not express; they speak to the understanding, as algebraical characters may do, but the passions, the affections, and the will, hear them not; these continue dormant and inactive, till we speak to them in the language of nature, to which they are all attention and obedience. It were easy to show, that the fine arts of the musician, the painter, the actor, and the orator, so far as they are expressive although the knowledge of them requires in us a delicate taste, a nice judgment, and much study and practice yet they are nothing else but the language of nature, which we brought into the world with us, but have unlearned by disuse, and so find the greatest diffi- culty in recovering it. Abolish the use of articulate sounds and writing among mankind for a century, and every man would be a 128 THE PHILOSOPHY OF REID. [Cn. IV., SEC. II. painter, an actor, and an orator. We mean not to affirm that such an expedient is practicable; or, if it were, that the advantage would counterbalance the loss; but that, as men are led by nature and necessity to converse together, they will use every mean in their power to make themselves understood; and where they cannot do this by artificial signs, they will do it, as far as possible, by natural ones: and he that understands perfectly the use of natural signs, must be the best judge in all the expressive arts. CH. V., SEC. I.] THE PHILOSOPHY OF REID. 129 CHAPTER V. OF TOUCH. Section I. OF HEAT AND COLD. THE senses which we have hitherto considered, are very simple and uniform, each of them exhibiting only one kind of sensation, and thereby indicating only one quality of bodies. By the ear we perceive sounds, and nothing else; by the palate, tastes; and by the nose., odours. These qualities are all likewise of one order, being all secondary qualities; whereas, by touch we perceive not one quality only, but many, and those of very different kinds. The chief of them are heat and cold, hardness and softness, roughness and smoothness, figure, solidity, motion, and extension. We shall con- sider these in order. As to heat and cold, it will easily be allowed that they are secondary qualities, of the same order with smell, taste, and sound. And, therefore, what hath been already said of smell, is easily applicable to them; that is, that the words heat and cold have each of them two significations; they sometimes signify certain sensations of the mind, which can have no existence when they are not felt, nor can exist anywhere but in a mind or sen- tient being; but more frequently they signify a quality in bodies, which, by the laws of nature, occasions the sen- sations of heat and cold in us a quality which, though connected by custom so closely with the sensation, that we cannot, without difficulty, separate them, yet hath not 130 THE PHILOSOPHY OF REID. [Cn. V. the least resemblance to it, and may continue to exist when there is no sensation at all. The sensations of heat and cold are perfectly known; for they neither are, nor can be, anything else than what we feel them to be; but the qualities in bodies which we call- heat and cold are unknown. They are only con- ceived by us, as unknown causes or occasions of the sen- sations to which we give the same names. But, though common sense says nothing of the nature of these quali- ties, it plainly dictates the existence of them; and to deny that there can be heat and cold when they are not felt, is an absurdity too gross to merit confutation. For what could be more absurd, than to say, that the ther- mometer cannot rise or fall, unless some person be pre- sent, or that the coast of Guinea would be as cold as Nova Zembla, if it had no inhabitants ? It is the business of philosophers to investigate, by proper experiments and induction, what heat and cold are in bodies. And whether they make heat a particu- lar element diffused through nature, and accumulated in the heated body, or whether they make it a certain vi- bration of the parts of the heated body; whether they determine that heat and cold are contrary qualities, as the sensations undoubtedly are contrary, or that heat only is a quality, and cold its privation: these questions are within the province of philosophy; for common sense says nothing on the one side or the other. But, whatever be the nature of that quality in bodies which we call heat, we certainly know this, that it can- not in the least resemble the sensation of heat. It is no less absurd to suppose a likeness between the sensation and the quality, than it would be to suppose that the pain of the gout resembles a square or a triangle. The simplest man that hath common sense, does not imagine the sensation of heat, or anything that resembles that sensation, to be in the fire. He only imagines that there is something in the fire which makes him and other SEC. II.] THE PHILOSOPHY OF REID. 13! sentient beings feel heat. Yet, as the name of heat, in common language, more frequently and more properly signifies this unknown something in the fire, than the sensation occasioned by it, he justly laughs at the phi- losopher who denies that there is any heat in the fire, and thinks that he speaks contrary to common sense. Section II. OF HARDNESS AND SOFTNESS. Let us next consider hardness and softness ; by which words we always understand real properties or qualities of bodies of which we have a distinct conception. When the parts of a body adhere so firmly that it cannot easily be made to change its figure, we call it hard ; when its parts are easily displaced, we call it soft. This is the notion which all mankind have of hardness and softness ; they are neither sensations, nor like any sensation ; they were real qualities before they were per- ceived by touch, and continue to be so when they are not perceived ; for if any man will affirm that diamonds were not hard tilf they were handled, who would reason with him ? There is, no doubt, a sensation by which we perceive a body to be hard or soft This sensation of hardness may easily be had, by pressing one's hand against the table, and attending to the feeling that ensues, setting aside, as much as possible, all thought of the table and its qualities, or of any external thing. But it is one thing to have the sensation, and another to attend to it, and make it a distinct object of reflection. The first is very easy; the last, in most cases, extremely difficult. We are so accustomed to use the sensation as a sign, and to pass immediately to the hardness signified, that, as far as appears, it was never made an object of thought, either by the vulgar or by philosophers ; nor has it a 132 THE PHILOSOPHY OF REID. [Cn. V. name in any language. There is no sensation more dis- tinct, or more frequent ; yet it is never attended to, but passes through the mind instantaneously, and serves only to introduce that quality in bodies, which, by a law of our constitution, it suggests. There are, indeed, some cases, wherein it is no difficult matter to attend to the sensation occasioned by the hard- ness of a body ; for instance, when it is so violent as to occasion considerable pain : then nature calls upon us to attend to it, and then we acknowledge that it is a mere sensation, and can only be in a sentient being. If a man runs his head with violence against a pillar, I appeal to him whether the pain he feels resembles the hardness of the stone, or if he can conceive anything like what he feels to be in an inanimate piece of matter. The attention of the mind is here entirely turned towards the painful feeling; and, to speak in the common language of mankind, he feels nothing in the stone, but feels a violent pain in his head. It is quite otherwise when he leans his head gently against the pillar ; for then he will tell you that he feels nothing in his head, but feels hardness in the stone. Hath he not a sensation in this case as well as in the other ? Undoubtedly he hath ; but it is a sensation which nature intended only as a sign of something in the stone ; and, accordingly, he instantly fixes his attention upon the thing signified ; and cannot, without great difficulty, attend so much to the sensation as to be persuaded that there is any such thing distinct from the hardness it signifies. But, however difficult it may be to attend to this fugitive sensation, to stop its rapid progress, and to dis- join it from the external quality of hardness, in whose shadow it is apt immediately to hide itself ; this is what a philosopher by pains and practice must attain, other- wise it will be impossible for him to reason justly upon this subject, or even to understand what is here advanced. For the last appeal, in subjects of this nature, must SEC. II.] THE PHILOSOPHY OF REID. 133 be to what a man feels and perceives in his own mind. It is indeed strange that a sensation which we have every time we feel a body hard, and which, conse- quently, we can command as often and continue as long as we please, a sensation as distinct and determinate as any other, should yet be so much unknown as never to have been made an object of thought and reflection, nor to have been honoured with a name in any language : that philosophers, as well as the vulgar, should have entirely overlooked it, or confounded it with that quality of bodies which we call hardness, to which it hath not the least similitude. May we not hence conclude, that the knowledge of the human faculties is but in its in- fancy ? that we have not yet learned to attend to those operations of the mind, of which we are conscious every hour of our lives ? that there are habits of inattention acquired very early, which are as hard to be overcome as other habits ? For I think it is probable, that the novelty of this sensation will procure some attention to it in* children at first ; but, being in nowise interesting in itself, as soon as it becomes familiar, it is overlooked, and the attention turned solely to that which it signifies. Thus, when one is learning a language, he attends to the sounds ; but when he is master of it, he attends only to the sense of what he would express. If this is the case, we must become as little children again, if we will be philosophers ; we must overcome this habit of inattention which has been gathering strength ever, since we began to think a habit, the usefulness of which, in common life, atones for the difficulty it creates to the philosopher in discovering the first principles of the human mind. The firm cohesion of the parts of a body, is no more like that sensation by which I perceive it to be hard, than the vibration of a sonorous body is like the sound I hear : nor can I possibly perceive, by my reason, any connec- tion between the one and the other, No man can give 134 THE PHILOSOPHY OF REID. [Cn. V. a reason, why the vibration of a body might not have given the sensation of smelling, and the effluvia of bodies affected our hearing, if it had so pleased our Maker. In like manner, no man can give a reason why the sen- sations of smell, or taste, or sound, might not have indicated hardness, as well as that sensation which, by our constitution, does indicate it. Indeed, no man can conceive any sensation to resemble any known quality of bodies. Nor can any man show, by any good argument, that all our sensations might not have been as they are, though no body, nor quality of body, had ever existed. Here, then, is a phenomenon of human nature, which comes to be resolved. Hardness of bodies is a thing that we conceive as distinctly, and believe as firmly, as anything in nature. We have no way of coming at this conception and belief, but by means of a certain sensa- tion of touch, to which hardness hath not the least simil- itude; nor can we, by any rules of reasoning, infer the one from the other. The question is, How we come by this conception and belief? First, as to the conception: Shall we call it an idea of sensation, or of reflection ? The last will not be affirmed; and as little can the first, unless we will call that an idea of sensation which hath no resemblance to any sensation. So that the origin of this idea of hardness, one of the most common and most distinct we have, is not to be found in all our systems of the mind: not even in those which have so copiously endeavoured to deduce all our notions from sensation and reflection. But, secondly, supposing we have got the conception of hardness, how come we by the belief of it ? Is it self- evident, from comparing the ideas, that such a sensation could not be felt, unless such a quality of bodies existed ? No. Can it be proved by probable or certain arguments ? No; it cannot. Have we got this belief, then, by tradi- tion, by education, or by experience ? No; it is not got SEC. III.] THE PHILOSOPHY OF REID. 135 in any of these ways. Shall we then throw off this be- lief as having no foundation in reason ? Alas ! it is not in our power; it triumphs over reason, and laughs at all the arguments of a philosopher. Even the author of the "Treatise of Human Nature," though he saw no reason for this belief, but many against it, could hardly conquer it in his speculative and solitary moments; at other times, he fairly yielded to it, and confesses that he found himself under a necessity to do so. What shall we say, then, of this conception, and this belief, which are so unaccountable and untractable ? I see nothing left, but to conclude, that, by an original principle of our constitution, a certain sensation of touch both suggests to the mind the conception of hardness, and creates the belief of it: or, in other words, that this sensation is a natural sign of hardness. And this I shall endeavour more fully to explain. Section III. OF NATURAL SIGNS. As in artificial signs there is often neither similitude between the sign and thing signified, nor any connec- tion that arises necessarily from the nature of the things, so it is also in natural signs. The word gold has no similitude to the substance signified by it; nor is it in its own nature more fit to signify this than any other sub- stance; yet, by habit and custom, it suggests this and no other. In like manner, a sensation of touch suggests hardness, although it hath neither similitude to hardness, nor, as far as we can perceive, any necessary connection with it. The difference betwixt these two signs lies only in this that, in the first, the suggestion is the effect of habit and custom; in the second, it is not the effect of habit, but of the original constitution of our minds. It appears evident from what hath been said on the 136 THE PHILOSOPHY OF REID. [Cn. V. subject of language, that there are natural signs as well as artificial; and particularly, that the thoughts, pur- poses, and dispositions of the mind, have their natural signs in the features of the face, the modulation of the voice, and the motion and attitude of the body: that, without a natural knowledge of the connection between these signs and the things signified by them, language could never have been invented and established among men: and, that the fine arts are all founded upon this connection, which we may call the natural language of mankind. It is now proper to observe, that there are different orders of natural signs, and to point out the different classes into which they may be distinguished, that we may more distinctly conceive the relation between our sensations and the things they suggest, and what we mean by calling sensations signs of external things. The first class of natural signs comprehends those whose connection with the thing signified is established by nature, but discovered only by experience. The whole of genuine philosophy consists in discovering such connections, and reducing them to general rules. The great Lord Verulam had a perfect comprehension of this, when he called it an interpretation of nature. No man ever more distinctly understood or happily ex- pressed the nature and foundation of the philosophic art. What is all we know of mechanics, astronomy, and optics, but connections established by nature, and dis- covered by experience or observation, and consequences deduced from them ? All the knowledge we have in agri- culture, gardening, chemistry, and medicine, is built upon the same foundation. And if ever our philosophy concerning the human mind is carried so far as to de- serve the name of science, which ought never to be de- spaired of, it must be by observing facts, reducing them to general rules, and drawing just conclusions from them. What we commonly call natural causes might, with more .SEC. III!] THE PHILOSOPHY OF REID. 137 propriety, be called natural signs, and what we call effects, the things signified. The causes have no proper efficiency or causality, as far as we know: and all we can certainly affirm is, that nature hath established a con- stant conjunction between them and the things called their effects; and hath given to mankind a disposition to observe those connections, to confide in their contin- uance, and to make use of them for the improvement of our knowledge, and increase of our power. A second class is that wherein the connection between the sign and thing signified, is not only established by nature, but discovered to us by a natural principle, with- out reasoning or experience. Of this kind are the nat- ural signs of human thoughts, purposes, and desires, which have been already mentioned as the natural lan- guage of mankind. An infant may be put into a fright by an angry countenance, and soothed again by smiles and blandishments. A child that has a good musical ear, may be put to sleep or to dance, may be made mer- ry or sorrowful, by the modulation of musical ^sounds. The principles of all the fine arts, and of what we call a fine taste, may be resolved into connections of this kind. A fine taste may be improved by reasoning and experience; bur if the first principles of it were not planted in our minds by nature, it could never be ac- quired. Nay, we have already made it appear, that a great part of this knowledge which we have by nature, is lost by the disuse of natural signs, and the substitution of artificial in their place. A third class of natural signs comprehends those which, though we never before had any notion or con- ception of the thing signified, do suggest it, or conjure it up, as it were, by a natural kind of magic, and at once give us a conception and create a belief of it. I shewed formerly, that our sensations suggest to us a sentient being or mind to which they belong a being which hath a permanent existence, although the sensa- 138 THE PHILOSOPHY OF REID. [Cn. V. tions are transient and of short duration a being which is still the same, while its sensations and other operations are varied ten thousand ways a being which hath the same relation to all that infinite variety of thoughts, pur- poses, actions, affections, enjoyments, and sufferings, which we are conscious of, or can remember. The conception of a mind is neither an idea of sensation nor of reflection; for it is neither like any of our sensations, nor like anything we are conscious of. The first con- ception of it, as well as the belief of it, and of the com- mon relation it bears to all that we are conscious of, or remember, is suggested to every thinking being, we do not know how. The notion of hardness in bodies, as well as the belief of it, are got in a similar manner; being, by an original principle of our nature, annexed to that sensation which we have when we feel a hard body. And so naturally and necessarily does the sensation convey the notion and belief of hardness, that hitherto they have been con- founded by the most acute inquirers into the principles of human nature, although they appear, upon accurate reflection, not only to be different things, but as unlike as pain is to the point of a sword. It may be observed, that, as the first class of natural signs I have mentioned is the foundation of true philoso- phy, and the second the foundation of the fine arts, or of taste so the last is the foundation of common sense a part of human nature which hath never been ex- plained. I take it for granted, that the notion of hardness, and the belief of it, is first got by means of that particular sensation which, as far back as we can remember, does invariably suggest it ; and that, if we had never had such a feeling, we should never have had any notion of hard- ness. I think it is evident, that we cannot, by reasoning from our sensations, collect the existence of bodies at all, far less any of their qualities. This hath been proved SEC. IV.] THE PHILOSOPHY OF REID. 139 by unanswerable arguments by the Bishop of Cloyne, and by the author of the "Treatise of Human Nature." It appears as evident that this connection between our sen- sations and the conception and belief of external exist- ences cannot be produced by habit, experience, educa- tion, or any principle of human nature that hath been admitted by philosophers. At the same time, it is a fact that such sensations are invariably connected with the conception and belief of external existences. Hence, by all rules of just reasoning, we must conclude that this connection is the effect of our constitution, and ought to be considered as an original principle of human nature, till we find some more general principle into which it may be resolved. * Section IV. OF HARDNESS, AND OTHER PRIMARY QUALITIES. Further, I observe that hardness is a quality, of which we have as clear and distinct a conception as of anything whatsoever. The cohesion of the parts of a body with more or less force, is perfectly understood, though its cause is not ; we know what it is, as well as how it affects the touch. It is, therefore, a quality of a quite different order from those secondary qualities we have already taken notice of, whereof we know no more nat- urally than that they are adapted to raise certain sensa- tions in us. If hardness were a quality of the same kind, it would be a proper inquiry for philosophers, what hardness in bodies is ? and we should have had various hypotheses about it, as well as about colour and heat. * This whole doctrine of natural signs, on which his philosophy is in a great measure established, was borrowed by Reid, in principle, and even in expression, from Berkeley. Compare "Minute Philoso- pher," Dial. IV., 7, n, 12; "New Theory of Vision," 144. 147; "Theory of Vision Vindicated," 38-43. H. 140 THE PHILOSOPHY OF REID. [Cn. V. But it is evident that any such hypothesis would be ridiculous. If any man should say, that hardness in bodies is a certain vibration of their parts, or that it is certain effluvia emitted by them which affect our touch in the manner we feel such hypotheses would shock common sense ; because we all know that, if the parts of a body adhere strongly, it is hard, although it should neither emit effluvia nor vibrate. Yet, at the same time, no man can say, but that effluvia or the vibration of the parts of a body, might have affected our touch, in the same manner that hardness now does, if it had so pleased the Author of our nature ; and, if either of these hypoth- eses is applied to explain a secondary quality such as smell, or taste, or sound, or colour, or heat there ap- pears no manifest absurdity in the supposition. The distinction betwixt primary and secondary quali- ties hath had several revolutions. Democritus and Epi- curus, and their followers, maintained it. Aristotle and the Peripatetics abolished it. Des Cartes, Malebranche, and Locke, revived it, and were thought to have put it in a very clear light. But Bishop Berkeley again discard- ed this distinction, by such proofs as must be con- vincing to those that hold the received doctrine of ideas. * Yet, after all, there appears to be a real foundation for it in the principles of our nature. What hath been said of hardness, is so easily appli- cable not only to its opposite, softness, but likewise to roughness and smoothness, to figure and motion, that we may be excused from making the application, which would only be a repetition of what hath been said. All these, by means of certain corresponding sensations of touch, are presented to the mind as real external quali- ties ; the conception and the belief of them are invariably * On this distinction of Primary and Secondary Qualities, see "Essays on the Intellectual Powers," Essay II., chap. 17, and Note D, at the end of the volume. H. SEC. V.] THE PHILOSOPHY OF REID. 141 connected with the corresponding sensations, by an original principle of human nature. Their sensations have no name in any language ; they have not only been overlooked by the vulgar, but by philosophers ; or, if they have been at all taken notice of, they have been confounded with the external qualities which they sug- gest. Section V. OF EXTENSION. It is further to be observed, that hardness and softness, roughness and smoothness, figure and motion, do all suppose extension, and cannot be conceived without it ; yet, I think it must, on the other hand, be allowed that, if we had never felt any thing hard or soft, rough or smooth, figured or moved, we should never have had a conception of extension ;* so that, as there is good ground to believe that the notion of extension could not be prior to that of other primary qualities, so it is cer- tain that it could not be posterior to the notion of any of them, being necessarily implied in them all.f Extension, therefore, seems to be a quality suggested to us, by the very same sensations which suggest the other qualities above mentioned. When I grasp a ball in my hand, I perceive it at once hard, figured, and ex- * According to Reid, Extension (Space) is a notion a posteriori, the result of experience. According to Kant, it is a priori y experi- ence only affording the occasions required by the mind to exert the acts, of which the intuition of space is a condition. To the former it is thus a contingent : to the latter, a necessary mental possession. H. f In this paragraph, to say nothing of others in the " Inquiry," Reid evidently excludes sight as a sense, through which the notion of extension or space, enters into the mind. In his later work, the " Essays on the Intellectual Powers," he, however, expressly allows that function to sight and touch, and to those senses alone. See Essay II., chap. 19, p. 262, quarto edition. H. 142 THE PHILOSOPHY OF REID. [Cn. V. tended. The feeling is very simple, and hath not the least resemblance to any quality of body. Yet it sug- gests to us three primary qualities perfectly distinct from one another, as well as from the sensation which indi- cates them. When I move my hand along the table, the feeling is so simple that I find it difficult to distin- guish it into things of different natures ; yet, it immedi- ately suggests hardness, smoothness, extension, and mo- tion things of very different natures, and all of them as distinctly understood as the feeling which suggests them. We are commonly told by philosophers, that we get the idea of extension by feeling along the extremities of a body, as if there was no manner of difficulty in the matter. I have sought, with great pains, I confess, to find out how this idea can be got by feeling ; but I have sought in vain. Yet it is one of the clearest and most distinct notions we have ; nor is there anything whatso- ever about which the human understanding can carry on so many long and demonstrative trains of reasoning. The notion of extension is so familiar to us from in- fancy, and so constantly obtruded by everything we see and feel, that we are apt to think it obvious how it comes into the mind ; but upon a narrower examination we shall find it utterly inexplicable. It is true we have feelings of touch, which every moment present extension to the mind ; but how they come to do so, is the ques- tion ; for those feelings do no more resemble extension, than they resemble justice or courage nor can the ex- istence of extended things be inferred from those feelings by any rules of reasoning ; so that the feelings we have by touch, can neither explain how we get the notion, nor how we come by the belief of extended things. What hath imposed upon philosophers in this matter is, that the feelings of touch, which suggest primary qualities, have no names, nor are they ever reflected upon. They pass through the mind instantaneously, SEC. V.) THE PHILOSOPHY OP REID. 143 and serve only to introduce the notion and belief of ex- ternal things, which, by our constitution, are connected with them. They are natural signs, and the mind im- mediately passes to the thing signified, without making the least reflection upon the sign, or observing that there was any such thing. Hence it hath always been taken for granted, that the ideas of extension, figure, and mo- tion, are ideas of sensation, which enter into the mind by the sense of touch, in the same manner as the sensa- tions of sound and smell do by the ear and nose. The sensations of touch are so connected, by our constitution, with the notions of extension, figure, and motion, that philosophers have mistaken the one for the other, and never have been able to discern that they were not only distinct things, but altogether unlike. However, if we will reason distinctly upon this subject, we ought to give names to those feelings of touch ; we must accustom ourselves to attend to them, and to reflect upon them, that we may be able to disjoin them from, and to compare them with, the qualities signified or suggested by them. The habit of doing this is not to be attained without pains and practice ; and till a man hath acquired this habit, it will be impossible for him to think distinctly, or to judge right, upon this subject. Let a man press his hand against the table he feels it hard. But what is the meaning of this ? The mean- ing undoubtedly is, that he hath a certain feeling of touch, from whickhe concludes, without any reasoning, or comparing ideas, that there is something external really existing, whose parts stick so firmly together, that they cannot be displaced without considerable force. There is here a feeling, and a conclusion drawn from it, or some way suggested by it. In order to compare these, we must view them separately, and then consider by what tie they are connected, and wherein they resem- ble one another. The hardness of the table is the con- clusion, the feeling is the medium by which we are led 144 TttE PHILOSOPHY OF REID. [CH. V, to that conclusion. Let a man attend distinctly to this medium, and to the conclusion, and he will perceive them to be as unlike as any two things in nature. The one is a sensation of the mind, which can have no ex- istence but in a sentient being ; nor can it exist one moment longer than it is felt ; the other is in the table, and we conclude, without any difficulty, that it was in the table before it was felt, and continues after the feel- ing is over. The one implies no kind of extension, nor parts, nor cohesion ; the other implies all these. Both, indeed, admit of degrees, and the feeling, beyond a cer- tain degree, is a species of pain ; but adamantine hard- ness does not imply the least pain. And as the feeling hath no similitude to hardness, so neither can our reason perceive the least tie or connec- tion between them ; nor will the logician ever be able to shew a reason why we should conclude hardness from this feeling, rather than softness, or any other quality whatsoever. But, in reality, all mankind are led by their constitution to conclude hardness from this feeling. The sensation of heat, and the sensation we have by pressing a hard body, are equally feelings ; nor can we, by reasoning, draw any conclusion from the one but what may be drawn from the other ; but, by our consti- tution, we conclude from the first an obscure or occult quality, of which we have only this relative conception, that it is something adapted to raise in us the sensation of heat ; from the second, we conclude a quality of which we have a clear and distinct conception to wit, the hardness of the body. Section VI. OF EXTENSION. To put this matter in another light, it may be proper to try, whether from sensation alone we can collect any SEC. VI.] THE PHILOSOPHY OF REID. 145 notion of extension, figure, motion, and space. I take it for granted, that a blind man hath the same notions of extension, figure, and motion, as a man that sees ; that Dr. Saunderson had the same notion of a cone, a cylinder, and a sphere, and of the motions and distances of the heavenly bodies, as Sir Isaac Newton. As sight, therefore, is not necessary for our acquiring those notions, we shall leave it out altogether in our inquiry into the first origin of them ; and shall suppose a blind man, by some strange distemper, to have lost all the experience, and habits, and notions he had got by touch ; not to have the least conception .of the existence, figure, dimensions, or extension, either of his own body, or of any other ; but to have all his knowledge of exter- nal things to acquire anew, by means of sensation, and the power of reason, which we suppose to remain entire. We shall, first, suppose his body fixed immovably in one place, and that he can only have the feelings of touch, by the application of other bodies to it. Suppose him first to be pricked with a pin this will, no doubt, give a smart sensation: he feels pain ; but what can he infer from it ? Nothing, surely, with regard to the ex- istence or figure of a pin. He can infer nothing from this species of pain, which he may not as well infer from the gout or sciatica. Common sense may lead him to think that this pain has a cause ; but whether this cause is body or spirit, extended or unextended, figured or not figured, he cannot possibly, from any principles he is supposed to have, form the least conjecture. Having had formerly no notion of body or of extension, the prick of a pin can give him none. Suppose, next, a body not pointed, but blunt, is ap- plied to his body with a force gradually increased until it bruises him. What has he got by this, but another sensation or train of sensations, from which he is able to conclude as little as from the former? A scirrhous tumour in any inward part of the body, by pressing upon 146 THE PHILOSOPHY OF REID. [CH. V. the adjacent parts, may give the same kind of sensation as the pressure of an external body, without conveying any notion but that of pain, which, surely, hath no re- semblance to extension. Suppose, thirdly, that the body applied to him touches a larger or a lesser part of his body. Can this give him any notion of its extension or dimensions ? To me it seems impossible that it should, unless he had some previous notion of the dimensions and figure of his own body, to serve him as a measure. When my two hands touch the extremities of a body, if I know them to be a foot asunder, I easily collect that the body is a foot long ; and, if I know them to' be five feet asunder, that it is five feet long ; but, if I know not what the distance of my hands is, I cannot know the length of the object they grasp ; and, if I have no previous notion of hands at all, or of distance between them, I can never get that notion by their being touched. Suppose, again, that a body is drawn along his hands or face, while they are at rest. Can this give him any notion of space or motion ? It no doubt gives a new feeling ; but how it should convey a notion of space or motion to one who had none before, I cannot conceive. The blood moves along the arteries and veins, and this motion, when violent, is felt : but I imagine no man, by this feeling, could get the conception of space or motion, if he had it not before. Such a motion may give a certain succession of feelings, as the colic may do ; but no feelings, nor any combination of feelings, can ever resemble space or motion Let us next suppose, that he makes some instinctive effort to move his head or his hand ; but that no motion follows, either on account of external resistance, or of palsy. Can this effort convey the notion of space and motion to one who never had it before? Surely it cannot. Last of all, let us suppose that he moves a limb by SEC. VI.] THE PHILOSOPHY OF REID. 147 instinct, without having had any previous notion of space or motion. He has here a new sensation, which accom- panies the flexure of joints, and the swelling of muscles. But how this sensation can convey into his mind the idea of space and motion, is still altogether mysterious and unintelligible. The motions of the heart and lungs are all performed by the contraction of muscles, yet give no conception of space or motion. An embryo in the womb has many such motions, and probably the feelings that accompany them, without any idea of space or motion. Upon the whole, it appears that our philosophers have imposed upon themselves and upon us, in pre- tending to deduce from sensation the first origin of our notions of external existences, of space, motion, and ex- tension,* and all the primary qualities of body that is, the qualities whereof we have the most clear and distinct conception. These qualities do not at all tally with any system of the human faculties that hath been advanced. They have no resemblance to any sensation, or to any operation of our minds ; and, therefore, they cannot be ideas either of sensation or of reflection. The very con- ception of them is irreconcilable to the principles of all our philosophic systems of the understanding. The be- lief of them is no less so. * That the notion of Space is a necessary condition of thought, and that, as such, it is inspossible to derive it from experience, has been cogently demonstrated by Kant. But that we may not, through sense,have empirically an immediate perception of some- thing extended, I have yet seen no valid reason to doubt. The a priori Conception does not exclude the a posteriori Perception ; and this latter cannot be rejected without belying the evidence of consciousness, which assures us that we are immediately cognizant, not only of a Setfb\it of a Not Se/f, not only of mind but of matter: and matter cannot be immediately known that is known as existing except as something extended. In this, however, I venture a step beyond Reid and Stewart, no less than beyond Kant; though I am convinced that the philosophy of the two former tended to this con- clusion, which is, in fact, that of the common sense of mankind, H, 148 THE PHILOSOPHY OF REID. [Cn. V. Section VII. OF THE EXISTENCE OF A MATERIAL WORLD. It is beyond our power to say when, or in what order, we came by our notions of these qualities. When we trace the operations of our minds as far back as memory and reflection can carry us, we find them already in pos- session of our imagination and belief, and quite familiar to the mind : but how they came first into its acquaint- ance, or what has given them so strong a hold of our be- lief, and what regard they deserve, are, no doubt, very important questions in the philosophy of human nature. Shall we, with the Bishop of Cloyne, serve them with a quo warranto, and have them tried at the bar of philos- ophy, upon the statute of the ideal system ? Indeed, in this trial they seem to have come off very pitifully ; for, although they had very able counsel, learned in the law viz., Des Cartes, Malebranche, and Locke, who said everything they could for their clients the Bishop of Cloyne, believing them to be aiders and abetters of heresy and schism, prosecuted them with great vigour, fully answered all that had been pleaded in their defence, and silenced their ablest advocates, who seem, for half a century past, to decline the argument, and to trust to the favour of the jury rather than to the strength of their pleadings. Thus, the wisdom of philosophy is set in opposition to the common sense of mankind. The first pretends to de- monstrate, a priori, that there can be no such thing as a material world; that sun, moon, stars, and earth, vegeta- ble and animal bodies, are, and can be nothing else, but sensations in the mind, or images of those sensations in the memory and imagination; that, like pain and joy, they can have no existence when they are not thought of. The last can conceive no otherwise of this opinion, than as a kind of metaphysical lunacy, and concludes SEC. VII.] THE PHILOSOPHY OF REID. 149 that too much learning is apt to make men mad; and that the man who seriously entertains this belief, though in other respects he may be a very good man, as a man may be who believes that he is made of glass; yet, surely he hath a soft place in his understanding, and hath been hurt by much thinking. This opposition betwixt philosophy and common sense, is apt to have a very unhappy influence upon the philosopher himself. He sees human nature in an odd, unamiable, and mortifying light He considers himself, and the rest of his species, as born under a necessity of believing ten thousand absurdities and contradictions, and endowed with such a pittance of reason as is just sufficient to make this unhappy discovery: and this is all the fruit of his profound speculations. Such notions of human nature tend to slacken every nerve of the soul, to put every noble purpose and sentiment out of counte- nance, and spread a melancholy gloom over the whole face of things. If this is wisdom, let me be deluded with the vulgar. I find something within me that recoils against it, and inspires more reverent sentiments of the human kind, and of the universal administration. Common Sense and Reason * have both one author; that Almighty Au- thor in all whose other works we observe a consistency, uniformity, and beauty which charm and delight the un- derstanding: there must, therefore, be some order and consistency in the human faculties, as well as in other parts of his workmanship. A man that thinks reverent- ly of his own kind, and esteems true wisdom and philos- ophy, will not be fond, nay, will be very suspicious, of such strange and paradoxical opinions. If they are false, they disgrace philosophy; and, if they are true, * The reader will again notice this and the other instances which follow, of the inaccuracy of Reid's language in his earlier work, con- stituting, as different, Reason and Common Sense. H. 150 THE PHILOSOPHY OF REID. [Cn. V. they degrade the human species, and make us justly ashamed of our frame. To what purpose is it for philosophy to decide against common sense in this or any other matter ? The belief of a material world is older, and of more authority, than any principles of philosophy. It declines the tribunal of reason,* and laughs at all the artillery of the logician. It retains its sovereign authority in spite of all the edicts of philosophy, and reason itself must stoop to its orders. Even those philosophers who have disowned the author- ity of our notions of an external material world, confess that they find themselves under a necessity of submitting to their power. Methinks, therefore, it were better to make a virtue of necessity; and, since we cannot get rid of the vulgar notion and belief of an external world, to reconcile our reason to it as well as we can; for, if Reason* should stomach and fret ever so much at this yoke, she cannot throw it off; if she will not be the servant of Common Sense, she must be her slave. In order, therefore, to reconcile Reason to Common Sense* in this matter, I beg leave to offer to the consid- eration of philosophers these two observations. First, That, in all this debate about the existence of a material world, it hath been taken for granted on both sides, that this same material world, if any such there be, must be the express image of our sensations ; that we can have no conception of any material thing which is not like some sensation in our minds; and particularly that the sen- sations of touch are images of extension, hardness, figure, and motion. Every argument brought against the exist- ence of a material world, either by the Bishop of Cloyne, or by the author of the " Treatise of Human Nature," sup- poseth this. If this is true, their arguments are conclu- sive and unanswerable; but, on the other hand, if it is * See last note. H. SEC. VII.] THE PHILOSOPHY OF REID 151 not true, there is no shadow of argument left. Have those philosophers, then, given any solid proof of this hypothesis, upon which the whole weight of so strange a system rests. No. They have not so much as at- tempted to do it. But, because ancient and modern philosophers have agreed in this opinion, they have taken it for granted. But let us, as becomes philosophers, lay aside authority; we need not, surely, consult Aristotle or Locke, to know whether pain be like the point of a sword. I have as clear a conception of extension, hard- ness, and motion, as I have of the point of a sword; and, with some pains and practice, I can form as clear a no- tion of the other sensations of touch as I have of pain. When I do so, and compare them together, it appears to me clear as daylight, that the former are not of kin to the latter, nor resemble them in any one feature. They are as unlike, yea as certainly and manifestly unlike, as pain is to the point of a sword. It may be true, that those sensations first introduced the material world to our acquaintance; it may be true, that it seldom or never appears without their company; but, for all that, they are as unlike as the passion of anger is to those features of the countenance which attend it. So that, in the sentence those philosophers have passed against the material world, there is an error persona. Their proof touches not matter, or any of its qualities; but strikes directly against an idol of their own imagina- tion, a material world made of ideas and sensations, which never had nor can have an existence. Secondly, The very existence of our conceptions of extension, figure and motion, since they are neither ideas of sensation nor reflection, overturns the whole ideal system, by which the material world hath been tried and condemned;* so that there hath been likewise in this sentence an error juris. *It only overturns that Idealism founded on the clumsy hypothe- sis of ideas being something different, both from the reality they 152 THE PHILOSOPHY OF REID, [Cn. V. It is a very fine and a just observation of Locke, that, as no human art can create a single particle of matter, and the whole extent of our power over the material world consists in compounding, combining, and disjoining the matter made to our hands; so, in the world of thought, the materials are all made by nature, and can only be variously combined and disjoined by us. So that it is impossible for reason or prejudice, true or false philosophy, to produce one simple notion or conception, which is not the work of nature, and the result of our constitution. The conception of extension, motion, and the other attributes of matter, cannot be the effect of error or prejudice; it must be the work of nature. And the power or faculty by which we acquire those concep- tions, must be something different from any power of the human mind that hath been explained, since it is neither sensation nor reflection. This I would, therefore, humbly propose, as an exper- imentum cruets, by which the ideal system must stand or fall; and it brings the matter to a short issue: Extension, figure, motion, may, any one or all of them, be taken for the subject of this experiment. Either they are ideas of sensation, or they are not. If any one of them can be shewn to be an idea of sensation, or to have the least resemblance to any sensation, I lay my hand upon my mouth, and give up all pretense to reconcile reason to common sense in this matter, and must suffer the ideal scepticism to triumph. But if, on the other hand, they are not ideas of sensation, nor like to any sen- sation, then the ideal system is a rope of sand, and all the laboured arguments of the sceptical philosophy against a material world, and against the existence of represent, and from the mind contemplating their representation, and which, also, derives all such ideas from without. This doctrine may subvert the Idealism of Berkeley, but it even supplies a basis for an Idealism like that of Fichte. H. SEC. VII.] THE PHILOSOPHY OP REID. 153 everything but impressions and ideas, proceed upon a false hypothesis. If our philosophy concerning the mind be so lame with regard to the origin of our notions of the clearest, most simple, and most familiar objects of thought, and the powers from which they are derived, can we expect that it should be more perfect in the account it gives of the origin of our opinions and belief? We have seen already some instances of its imperfection in this respect: and, perhaps, that same nature which hath given us the power to conceive things altogether unlike to any of our sensations, or to any operation of our minds, hath like- wise provided for our belief of them, by some part of our constitution hitherto not explained. Bishop Berkeley hath proved, beyond the possibility of reply, that we cannot by reasoning infer the existence of matter from our sensations ; and the author of the "Treatise of Human Nature" hath proved no less clearly, that we cannot by reasoning infer the existence of our own or other minds from our sensations. But are we to admit nothing but what can be proved by reasoning? Then we must be sceptics indeed, and believe nothing at all. The author of the "Treatise of Human Nature" appears to me to be, but a half-sceptic. He hath not followed his principles so far as they lead him; but, after having, with unparalleled intrepidity and success, com- bated vulgar prejudices, when he had but one blow to strike, his courage fails him, he fairly lays down his arms, and yields himself a captive to the most common of all vulgar prejudices I mean the belief of the existence of his own impressions and ideas. I beg, therefore, to have the honour of making an ad- dition to the sceptical system, without which I conceive it cannot hang together. I affirm, that the belief of the existence of impressions and ideas, is as little supported by reason, as that of the existence of minds and bodies. No man ever did or could offer any reason for this belief. 1$4 THE PHILOSOPHY OF REID. [CH, V. Des Cartes took it for granted, that he thought, and had sensations and ideas; so have all his followers done. Even the hero of scepticism hath yielded this point, I crave leave to say, weakly and imprudently. I say so, because I am persuaded that there is no principle of his philosophy that obliged him to make this concession. And what is there in impressions and ideas so formida- ble, that this all-conquering philosophy, after triumph- ing over every other existence, should pay homage to them? Besides, the concession is dangerous: for belief is of such a nature, that, if you leave any root, it will spread; and you may more easily pull it up altogether, than say, Hitherto shalt thou go and no further: the ex- istence of impressions and ideas I give up to thee; but see thou pretend to nothing more. A thorough and con- sistent sceptic will never, therefore, yield this point; and while he holds it, you can never oblige him to yield any- thing else. To such a sceptic I have nothing to say; but of the semi-sceptics, I should beg to know, why they believe the existence of their impressions and ideas. The true reason I take to be, because they cannot help it ; and the same reason will lead them to believe many other things. All reasoning must be from first principles ; and for first principles no other reason can be given but this, that, by the constitution of our nature, we are under a necessity of assenting to them. Such principles are parts of our constitution, no less than the power of think- ing: reason can neither make nor destroy them; nor can it do anything without them: it is like a telescope, which may help a man to see farther, who hath eyes; but, with- out eyes, a telescope shews nothing at all. A mathema- tician cannot prove the truth of his axioms, nor can he prove anything, unless he takes them for granted. We cannot prove the existence of our minds, nor even of our thoughts and sensations. A historian, or a witness, can SEC. VII.] THE PHILOSOPHY OF REID. 155 prove nothing, unless it is taken for granted that the memory and senses may be trusted. A natural philoso- pher can prove nothing, unless it is taken for granted that the course of nature is steady and uniform. How or when I got such first principles, upon which I build all my reasoning, I know not; for I had them be- fore I can remember : but I am sure they are parts of my constitution, and that I cannot throw them off. That our thoughts and sensations must have a subject, which we call ourself, is not therefore an opinion got by reason- ing, but a natural principle. That our sensations of touch indicate something external, extended, figured, hard or soft, is not a deduction of reason, but a natural principle. The belief of it, and the very conception of it, are equally parts of our constitution. If we are de- ceived in it, we are deceived by Him that made us, and there is no remedy. * I do not mean to affirm, that the sensations of touch do, from the very first, suggest the same notions of body and its qualities which they do when we are grown up. Perhaps Nature is frugal in this, as in her other opera- tions. The passion of love, with all its concomitant * The philosophers who Have most loudly appealed to the veraci- ty of God, and the natural conviction of mankind, in refutation of certain obnoxious conclusions, have too often silently contradicted that yeracity and those convictions, when opposed to certain favour- ite opinions. But it is evident that such authority is either good for all, or good for nothing. Our natural consciousness assures us (and \h&fact of that assurance is admitted by philosophers of all opin- ions) that we have an immediate knowledge of the very things them- selves of an external and extended world; and, on the ground of this knowledge alone, is the belief of mankind founded, that such a world really exists. Reid ought, therefore, either to have given up his doctrine of the mere suggestion of extension, &c., as subjective notions, on the occasion of sensation, or not to appeal to the Divine veracity, and the common sense of mankind, in favour of conclu- sions of which that doctrine subverts the foundation. In this incon- sistency, Reid has, however, besides Des Cartes, many distinguished copartners. H. 156 THE PHILOSOPHY OF REID. |CH.V. sentiments and desires, is naturally suggested by the perception of beauty in the other sex; yet the same per- ception does not suggest the tender passion till a certain period of life. A blow given to an infant, raises grief and lamentation; but when he grows up, it as naturally stirs resentment, and prompts him to resistance. Per- haps a child in the womb, or for some short period of its existence, is merely a sentient being; the faculties by which it perceives an external world, by which it reflects on its own thoughts, and existence, and relation to other things, as well as its reasoning and moral faculties, un- fold themselves by degrees; so that it is inspired with the various principles of common sense, as with the passions of love and resentment, when it has occasion for them. Section VIII. OF THE SYSTEMS OF PHILOSOPHERS CONCERNING THE SENSES. All the systems of philosophers about our senses and their objects have split upon this rock, of not distin- guishing properly sensations which can have no existence but when they are felt, from the things suggested by them. Aristotle with as distinguishing a head as ever applied to philosophical disquisitions confounds these two; and makes every sensation to be the form, without the matter, of the thing perceived by it. As the impres- sion of a seal upon wax has the form of the seal but nothing of the matter of it, so he conceived our sensa- tions to be impressions upon the mind, which bear the image, likeness, or form of the external thing perceived, without the matter of it. Colour, sound, and smell, as well as extension, figure, and hardness, are, according to him, various forms of matter: our sensations are the same forms imprinted on the mind, and perceived in its own intellect. It is evident from this, that Aristotle made no distinction between primary and secondary qualities of SEC. VIII. ] THE PHILOSOPHY OF REID. 157 bodies, although that distinction was made by Democri- tus, Epicurus, and others of the ancients. Des Cartes, Malebranche, and Locke, revived the dis- tinction between primary and secondary qualities ; but they made the secondary qualities mere sensations, and the primary ones resemblances of our sensations. They maintained that colour, sound, and heat, are not any- thing in bodies, but sensations of the mind ; at the same time, they acknowledged some particular texture or modification of the body to be the cause or occasion of those sensations ; but to this modification they gave no name. Whereas, by the vulgar, the names of colour, heat, and sound, are but rarely applied to the sensations, and most commonly to those unknown causes of them, as hath been already explained. The constitution of our nature leads us rather to attend to the things signified by the sensation than to the sensation itself, and to give a name to the former rather than to the latter. Thus we see, that, with regard to secondary qualities, these philosophers thought with the vulgar, and with common sense. Their paradoxes were only an abuse of words ; for when they maintain, as an important modern dis- covery, that there is no Jieat in the fire, they mean no more, than that the fire does not feel heat, which every one knew before. With regard to primary qualities, these philosophers erred more grossly. They indeed believed the existence of those qualities ; but they did not at all attend to the sensations that suggest them, which, having no names, have been as little considered as if they had no existence. They were aware that figure, extension, and hardness, are perceived by means of sensations of touch ; whence they rashly concluded, that these sensations must be images and resemblances of figure, extension, and hardness. The received hypothesis of ideas naturally led them to this conclusion: and indeed cannot consist with any other ; for, according to that hypothesis, external things *5& THE PHILOSOPHY OF REID. [Cn. V. must be perceived by means of images of them in the mind ; and what can those images of external things in the mind be, but the sensations by which we perceive them ? This, however, was to draw a conclusion from a hy- pothesis against fact. We need not have recourse to any hypothesis to know what our sensations are, or what they are like. By a proper degree of reflection and at- tention we may understand them perfectly, and be as certain that they are not like any quality of body, as we can be, that the toothache is not like a triangle. How a sensation should instantly make us conceive and be- lieve the existence of an external thing altogether un- like to it, I do not pretend to know; and when I say that the one suggests the other, I mean not to explain the manner of thek connection, but to express a fact, which every one may be conscious of namely, that, by a law of our nature, such a conception and belief constantly and immediately follow the sensation. Bishop Berkeley gave new light to this subject, by shewing, that the qualities of an inanimate thing, such as matter is conceived to be, cannot resemble any sen- sation; that it is impossible to conceive anything like the sensations of our minds, but the sensations of other minds. Every one that attends properly to his sensa- tions must assent to this : yet it had escaped all the philos- ophers that came before Berkeley; it had escaped even the ingenious Locke, who had so much practised reflec- tion on the operations of his own mind. So difficult it is to attend properly even to our own feelings. They are so accustomed to pass through the mind unobserved and instantly to make way for that which nature intended them to signify, that it is extremely difficult to stop, and survey them ; and when we think we have acquired this power, perhaps the mind still fluctuates between the sensation and its associated quality, so that they mix to- gether, and present something to the imagination that is SEC. VIII.] THE PHILOSOPHY OF REID. 159 compounded of both. Thus, in a globe or cylinder, whose opposite sides are quite unlike in colour, if you turn it slowly, the colours are perfectly distinguishable and their dissimilitude is manifest; but if it is turned fast, they lose their distinction, and seem to be of one and the same colour. No succession can be more quick than that of tangi- ble qualities to the sensations with which nature has as- sociated them ; but when one has once acquired the art of making them separate and distinct objects of thought, he will then clearly perceive that the maxim of Bishop Berkeley, above-mentioned, is self-evident; and that the features of the face are not more unlike to a passion of the mind which they indicate, than the sensations of touch are to the primary qualities of body. But let us observe what use the Bishop makes of this important discovery. Why, he concludes, that we can have no conception of an inanimate substance, such as matter is conceived to be, or of any of its qualities ; and that there is the strongest ground to believe that there is no existence in nature but minds, sensations, and ideas ; if there is any other kind of existence, it must be what we neither have nor can have any conception of. But how does this folloV? Why, thus: We can have no conception of anything but what resembles some sen- sation or idea in our minds ; but the sensations and ideas in our minds can resemble nothing but the sensations and ideas in other minds ; therefore, the conclusion is evident. This argument, we see, leans upon two propo- sitions. The last of them the ingenious author hath, indeed, made evident to all that understand his reason- ing, and can attend to their own sensations: but the first proposition he never attempts to prove ; it is taken from the doctrine of ideas, which hath been so universally re- ceived by philosophers, that it was thought to need no proof. We may here again observe, that this acute writer ar- 160 THE PHILOSOPHY OF REID. [CH. V. gues from a hypothesis against fact, and against the com- mon sense of mankind. That we can have no concep- tion of anything, unless there is some impression, sensa- tion, or idea, in our minds which resembles it, is indeed an opinion which hath been very generally received among philosophers ; but it is neither self-evident, nor hath it been clearly proved ; and therefore it hath been more reasonable to call in question this doctrine of philoso- phers, than to discard the material world, and by that means expose philosophy to the ridicule of all men who will not offer up common sense as a sacrifice to meta- physics. We ought, however, to do this justice both to the Bishop of Cloyne and to the author of the " Treatise of Human Nature," to acknowledge, that their conclusions are justly drawn from the doctrine of ideas, which has been so universally received. On the other hand, from the character of Bishop Berkeley, and of his predecessors, Des Cartes, Locke, and Malebranche, we may venture to say, that, if they had seen all the consequences of this doctrine, as clearly as the author before mentioned did, they would -have suspected it vehemently, and examined it more carefully than they appear to have done. The theory of ideas, like the Trojan horse, had a specious appearance both of innocence and beauty ; but if those philosophers had known that it carried in its belly death and destruction to all science and common sense, they would not have broken down their walls to give it admittance. That we have clear and distinct conceptions of exten- sion, figure, motion, and other attributes of body, which are neither sensations, nor like any sensation, is a fact of which we may be as certain as that we have sensations. And that all mankind have a fixed belief of an external material world a belief which is neither got by reason- ing nor education, and a belief which we cannot shake off, even when we seem to have strong arguments against SEC. VIII.] THE PHILOSOPHY OF REID. l6l it and no shadow of argument for it is likewise a fact, for which we have all the evidence that the nature of the thing admits. These facts are phaenomena of human nature, from which we may justly argue against any hypothesis, however generally received. But to argue from a hypothesis against facts, is contrary to the rules of true philosophy. 162 THE PHILOSOPHY OF REID. [C.H. VI. CHAPTER VI. OF SEEING. Section I. THE EXCELLENCE AND DIGNITY OF THIS FACULTY. THE advances made in the knowledge of optics in the last age and in the present, and chiefly the discoveries of Sir Isaac Newton, do honour, not to philosophy only, but to human nature. Such discoveries ought for ever to put to shame the ignoble attempts of our modern sceptics to depreciate the human understanding, and to dispirit men in the search of truth, by representing the human faculties as fit for nothing but to lead us into absurdities and contradictions. Of the faculties called the five senses, sight is without doubt the noblest. The rays of light, which minister to this sense, and of which, without it, we could never have had the least conception, are the most wonderful and astonishing part of the inanimate creation. We must be satisfied of this, if we consider their extreme minuteness; their inconceivable velocity; the regular variety of colours which they exhibit; the invariable laws according to which they are acted upon by other bodies, in their reflections, inflections, and refractions, without the least change of their original properties ; and the facility with which they pervade bodies of great density and of the closest texture, without resistance, without crowding or disturb- ing one another, without giving the least sensible impulse to the lightest bodies. The structure of the eye, and of all its appurtenances, the admirable contrivances of nature for performing all SEC. I.] THE PHILOSOPHY OF REID. 163 its various external and internal motions, and the variety in the eyes of different animals, suited to their several natures and ways of life, clearly demonstrate this organ to be a masterpiece of Nature's work. And he must be very ignorant of what hath been discovered about it, or have a very strange cast of understanding, who can seri- ously doubt whether or not the rays of light and the eye were made for one another, with consummate wisdom, and perfect skill in optics. If we shall suppose an order of beings, endued with every human faculty but that of sight, how incredible would it appear to such beings, accustomed only to the slow informations of touch, that, by the addition of an organ consisting of a ball and socket of an inch diam- eter, they might be enabled, in an instant of time, without changing their place to perceive the dis- position of a whole army or the order of a battle, the figure of a magnificent palace or all the variety of a landscape ! If a man were by feeling to find out the fig- ure of the peak of Teneriffe, or even of St. Peter's Church at Rome, it would be the work of a lifetime. It would appear still more incredible to such beings as we have supposed, if they were informed of the dis- coveries, which may be made by this little organ in things far beyond the reach of any other sense : that by means of it we can find our way in the pathless ocean ; that we can traverse the globe of the earth, determine its figure and dimensions, and delineate every region of it; yea, that we can measure the planetary orbs, and make discoveries in the sphere of the fixed stars. Would it not appear still more astonishing to such beings, if they should be farther informed, that, by means of this same organ, we can perceive the tempers and dis- positions, the passions and affections, of our fellow- creatures, even when they want most to conceal them ? that, when the tongue is taught most artfully to lie and dissemble, the hypocrisy should appear in the counte- 164 THE PHILOSOPHY OF REID. [Cn. VI. * nance to a discerning eye ? and that, by this organ, we can often perceive what is straight and what is crooked in the mind as well as in the body ? How many myste- rious things must a blind man believe, if he will give credit to the relations of those that see ? Surely he needs as strong a faith as is required of a good Christian. It is not therefore without reason that the faculty of seeing is looked upon, not only as more noble than the other senses, but as having something in it of a na- ture superior to sensation. The evidence of reason is called seeing, not feeling, smelling, or tasting. Yea, we are wont to express the manner of the Divine knowledge by seeing, as that kind of knowledge which is most per- fect in us. Section IL SIGHT DISCOVERS ALMOST NOTHING WHICH THE BLIND MAY NOT COMPREHEND THE REASON OF THIS. Notwithstanding what hath been said of the dignity and superior nature of this faculty, it is worthy of our observation, that there is very little of the knowledge acquired by sight, that may not be communicated to a man born blind. One who never saw the light, may be learned and knowing in every science, even in optics ; and may make discoveries in every branch of philosophy. He may understand as much as another man, not only of the order, distances, and motions of the heavenly bodies ; but of the nature of light, and of the laws of the reflection and refraction of its rays. He may un- derstand distinctly how those laws produce the phaenom- ena of the rainbow, the prism, the camera obscura, and the magic lanthorn, and all the powers of the micro- scope and telescope. This is a fact sufficiently attested by experience. In order to perceive the reason of it, we must distin- guish the appearance that objects make to the eye, from SEC. 11.1 THE PHILOSOPHY OF REID. l6$ the things suggested by that appearance ; and again, in the visible appearance of objects, we must distinguish the appearance of colour from the appearance of exten- sion, figure, and motion. First, then, as to the visible appearance of the figure, and motion, and extension of bodies, I conceive that a man born blind may have a distinct notion, if not of the very things, at least of some- thing extremely like to them. May not a blind man be made to conceive that a body moving directly from the eye, or directly towards it, may appear to be at rest ? and that the same motion may appear quicker or slower, ac- cording as it is nearer to the eye or farther off, more direct or more oblique ? May he not be made to con- ceive, that a plain surface, in a certain position, may ap- pear as a straight line, and vary its visible figure, as its position, or the position of the eye, is varied? that a circle seen obliquely will appear an ellipse ; and a square, a rhombus, or an oblong rectangle ? Dr. Saun- derson understood the projection of the sphere, and the common rules of perspective ; and if he did, he must have understood all that I have mentioned. If there were any doubt of Dr. Saunderson's understanding these things, I could mention my having heard him say in conversation, that he found great difficulty in under- standing Dr. Halley's demonstration of that proposition, that the angles made by the circles of the sphere, are equal to the angles made by their representatives in the stereographic projection ; but, said he, when I laid aside that demonstration, and considered the proposition in my own way, I saw clearly that it must be true. Another gentleman, of undoubted credit and judgment in these matters, who had part in this conversation, remembers it distinctly. As to the appearance of colour, a blind man must be more at a loss ; because he hath no perception that resem- bles it. Yet he may, by a kind of analogy, in part supply this defect. To those who see, a scarlet colour signifies r66 THE PHILOSOPHY OF REID. [Cn. VI. an unknown quality in bodies, that makes to the eye an appearance which they are well acquainted with and have often observed to a blind man, it signifies an un- known quality, that makes to the eye an appearance which he is unacquainted with. But he can conceive the eye to be variously affected by different colours, as the nose is by different smells, or the ear by different sounds. Thus he can. conceive scarlet to differ from blue, as the sound of a trumpet does from that of a drum; or as the smell of an orange differs from that of an ap- ple. It is impossible to know whether a scarlet colour has the same appearance to me which it hath to another man ; and, if the appearance of it to different persons differed as much as colour does from sound, they might never be able to discover this difference. Hence it ap- pears obvious, that a blind man might talk long about colours distinctly and pertinently ; and, if you were to examine him in the dark about the nature, composition, and beauty of them, he might be able to answer, so as not to betray his defect. We have seen how far a blind man may go in the knowledge of the appearances which things make to the eye. As to the things which are suggested by them or inferred from them, although he could never discover them of himself, yet he may understand them perfectly by the information of others. And everything of this kind that enters into our minds by the eye, may enter into his by the ear. Thus, for instance, he could never, if left to the direction of his own faculties, have dreamed of any such thing as light ; but he can be informed of every- thing we know about it. He can conceive, as distinctly as we, the minuteness and velocity of its rays, their vari- ous degrees of refrangibility and reflexibility, and all the magical powers and virtues of that wonderful element. He could never of himself have found out, that there are such bodies as the sun, moon, and stars ; but he may be informed of all the noble discoveries of astronomers, SEC. II.] THE PHILOSOPHY OF REID. 167 about their motions, and the laws of nature by which they are regulated. Thus, it appears, that there is very little knowledge got by the eye, which may not be com- municated by language to those who have no eyes. If we should suppose that it were as uncommon for men to see as it is to be born blind, would not the few who had this rare gift appear as prophets and inspired teachers to the many ? We conceive inspiration to give a man no new faculty, but to communicate to him, in a new way, and by extraordinary means, what the facul- ties common to mankind can apprehend, and what he can communicate to others by ordinary means. On the supposition we have made, sight would appear to the blind very similar to this ; for the few who had this gift, could communicate the knowledge acquired by it tc those who had it not. They could not, indeed, convey to the blind any distinct notion of the manner in which they acquired this knowledge. A ball and socket would seem, to a blind man, in this case, as improper an instru- ment for acquiring such a variety and extent of know- ledge, as a dream or a vision. The manner in which a man who sees, discerns so many things by means of the eye, is as unintelligible to the blind, as the manner in which a man may be inspired with knowledge by the Almighty, is to us. Ought the blind man, therefore, without examination, to treat all pretences to the gift of seeing as imposture ? Might he not, if he were candid and tractable, find reasonable evidence of the reality of this gift in others, and draw great advantages from it to himself? The distinction we have made between the visible ap- pearances of the objects of sight, and things suggested by them, is necessary to give us a just notion of the in- tention of nature in giving us eyes. If we attend duly to the operation of our mind in the use of this faculty, we shall perceive that the visible appearance of objects is hardly ever regarded by us. It is not at all made an 168 ' THE PHILOSOPHY OF REID. [Cn. VI. object of thought or reflection, but serves only as a sign to introduce to the mind something else, which may be distinctly conceived by those who never saw. Thus, the visible appearance of things in my room varies almost every hour, according as the day is clear or cloudy, as the sun is in the east, or south, or west, and as my eye is in one part of the room or in another ; but I never think of these variations, otherwise than as signs of morning, noon, or night, of a clear or cloudy sky. A book or a chair has a different appearance to the eye, in every different distance and position ; yet we conceive it to be still the same; and, overlooking the appearance, we immediately conceive the real figure, dis- tance, and position of the body, of which its visible or perspective appearance is a sign and indication. When I see a man at the distance of ten yards, and afterwards see him at the distance of a hundred yards, his visible appearance, in its length, breadth, and all its linear proportions, is ten times less in the last case than it is in the first ; yet I do not conceive him one inch di- minished by this diminution of his visible figure. Nay, I do not in the least attend to this diminution, even when I draw from it the conclusion of his being at a greater distance. For such is the subtilty of the mind's opera- tion in this case, that we draw the conclusion, without perceiving that ever the premises entered into the mind. A thousand such instances might be produced, in order to shew that the visible appearances of objects are in- tended by nature only as signs or indications ; and that the mind passes instantly to the things signified, without making the least reflection upon the sign, or even per- ceiving that there is any such thing. It is in a way some- what similar, that the sounds of a language, after it is be- come familiar, are overlooked, and we attend only to the things signified by them. It is therefore a just and important observation of the Bishop of Cloyne, That the visible appearance of objects SEC. III.] THE PHILOSOPHY Of RElD. 169 is a kind of language used by nature, to inform us of their distance, magnitude, and figure. And this obser- vation hath been very happily applied by that ingenious writer, to the solution of some phaenomena in optics, which had before perplexed the greatest masters in that science. The same observation is further improved by the judicious Dr. Smith, in his Optics, for explaining the apparent figure of the heavens, and the apparent distances and magnitudes of objects seen with glasses, or by the naked eye. Avoiding as much as possible the repetition of what hath been said by these excellent writers, we shall avail ourselves of the distinction between the signs that nature useth in this visual language, and the things signified by them; and in what remains to be said of sight, shall first make some observations upon the signs. Section HI. OF THE VISIBLE APPEARANCES OF OBJECTS. In this section we must speak of things which are never made the object of reflection, though almost every moment presented to the mind. Nature intended them only for signs ; and in the whole course of life they are put to no other use. The mind has acquired a con- firmed and inveterate habit of inattention to them ; for they no sooner appear, than quick as lightning the thing signified succeeds, and engrosses all our regard. They have no name in language ; and, although we are con- scious of them when they pass through the mind, yet their passage is so quick and so familiar, that it is abso- lutely unheeded ; nor do they leave any footsteps of them- selves, either in the memory or imagination. That this is the case with regard to the sensations of touch, hath been shewn in the last chapter ; and it holds no less with regard to the visible appearances of objects. 170 THE PHILOSOPHY OF REID. tCn. VI. I cannot therefore entertain the hope of being intelligi- ble to those readers who have not, by pains and prac- tice, acquired the habit of distinguishing the appearance of objects to the eye, from the judgment which we form by sight of their colour, distance, magnitude, and figure. The only profession in life wherein it is necessary to make this distinction, is that of painting. The painter hath occasion for an abstraction, with regard to visible objects, somewhat similar to that which we here require : and this indeed is the most difficult part of his art. For it is evident, that, if he could fix in his imagination the visible appearance of objects, without confounding it with the things signified by that appearance, it would be as easy for him to paint from the life, and to give every figure its proper shading and relief, and its perspective proportions, as it is to paint from a copy. Perspective, shading, giving relief, and colouring, are nothing else but copying the appearance which things make to the eye. We may therefore borrow some light on the subject of visible appearance from this art. Let one look upon any familiar object, such as a book, at different distances and in different positions : is he not able to affirm, upon the testimony of his sight, that it is the same book, the same object, whether seen at the dis- tance of one foot or of ten, whether in one position or another ; that the colour is the same, the dimensions the same, and the figure the same, as far as the eye can judge ? This surely must be acknowledged. The same individual object is presented to the mind, only placed at different distances and in different positions. Let me ask, in the next place, Whether this object has the same appearance to the eye in these different distances ? In- fallibly it hath not. For, First, However certain our judgment may be that the colour is the same, it is as certain that it hath not the same appearance at different distances. There is a cer- tain degradation of the colour, and a certain confusion SEC. III.] THE PHILOSOPHY OF REID. 171 and indistinctness of the minute parts, which is the natu- ral consequence of the removal of the object to a greater distance. Those that are not painters, or critics in painting, overlook this ; and cannot easily be persuaded, that the colour of the same object hath a different appear- ance at the distance of one foot and of ten, in the shade and in the light. But the masters in painting know how, by the degradation of the- colour and the confusion of the minute parts, figures which are upon the same canvas, and at the same distance from the eye, may be made to represent objects which are at the most unequal distances. They know how to make the ob- jects appear to be of the same colour, by making their pictures really of different colours, according to their distances or shades. Secondly, Every one who is acquainted with the rules of perspective, knows that the appearance of the figure of the book must vary in every different position: yet if you ask a man that has no notion of perspective, whether the figure of it does not appear to his eye to be the same in all its different positions ? he can with a good con- science affirm that it does. He hath learned to make allowance for the variety of visible figure arising from the difference of position, and to draw the proper con- clusions from it. But he draws these conclusions so readily and habitually, as to lose sight of the premises : and therefore where he hath made the same conclusion, he conceives the visible appearance must have been the same. Thirdly, Let us consider the apparent magnitude or dimensions of the book. Whether I view it at the dis- tance of one foot or of ten feet, it seems to be about seven inches long, five broad, and one thick. I can judge of these dimensions very nearly by the eye, and I judge them to be the same at both distances. But yet it is certain, that, at the distance of one foot, its visible length and breadth is about ten times as great as at the distance of 172 THE PHILOSOPHY OF REID. [Cn. VI. ten feet ; and consequently its surface is about a hun- dred times as great. This great change of apparent magnitude is altogether overlooked, and every man is apt to imagine, that it appears to the eye of the same size at both distances. Further, when I look at the book, it seems plainly to have three dimensions, of length, breadth, and thickness : but it is certain that the visible appearance hath no more than two, and can be exactly represented upon a canvas which hath only length and breadth. In the last place, does not every man, by sight, per- ceive the distance of the book from his eye ? Can he not affirm with certainty, that in one case it is not above one foot distant, that in another it is ten ? Nevertheless, it appears certain, that distance from the eye is no im- mediate object of sight. There are certain things in the visible appearance, which are signs of distance from the eye, and from which, as we shall afterwards shew, we learn by experience to judge of that distance within cer- tain limits ; but it seems beyond doubt, that a man born blind, and suddenly made to see, could form no judg- ment at first of the distance of the objects which he saw. The young man couched by Cheselden thought, at first, that everything he saw touched his eye, and learned only by experience to judge of the distance of visible objects. I have entered into this long detail, in order to shew that the visible appearance of an object is extremely different from the notion of it which experience teaches us to form by sight ; and to enable the reader to attend to the visible appearance of colour, figure, and extension, in visible things, which is no common object of thought, but must be carefully attended to by those who would enter into the philosophy of this sense, or would com- prehend what shall be said upon it. To a man newly made to see, the visible appearance of objects would be the same as to us ; but he would see nothing at all of SEC.IV.] THE PHILOSOPHY OF REID. 173 their real dimensions, as we do. He could form no conjecture, by means of his sight only, how many inches or feet they were in length, breadth, or thickness. He could perceive little or nothing of their real figure ; not could he discern that this was a cube, that a sphere; that this was a cone, and that a cylinder. His eye could not inform him that this object was near, and that more remote. The habit of a man or of a woman, which appeared to us of one uniform colour, variously folded and shaded, would present to his eye neither fold nor shade, but variety of colour. In a word, his eyes, though ever so perfect, would at first give him almost no information of things without him. They would indeed present the same appearances to him as they do to us, and speak the same language ; but to him it is an un- known language; and, therefore, he would attend only to the signs, without knowing the signification of them, whereas to us it is a language perfectly familiar ; and, therefore, we take no notice of the signs, but attend only to the thing signified by them. Section IV. THAT COLOUR IS A QUALITY OF BODIES, NOT A SENSATION OF THE MIND. BY colour, all men, who have not been tutored by modern philosophy, understand, not a sensation of the mind, which can have no existence when it is not per- ceived, but a quality or modification of bodies, which continues to be the same whether it is seen -or not. The scarlet-rose which is before me, is still a scarlet-rose when I shut my eyes, and was so at midnight when no eye saw it. The colour remains when the appearance ceases; it remains the same when the appearance changes. For when I view this scarlet-rose through a pair of green spectacles, the appearance is changed; 174 THE PHILOSOPHY OF REID. [CH.V1. but I do not conceive the colour of the rose changed. To a person in the jaundice, it has still another appear- ance; but he is easily convinced that the change is in his eye, and not in the colour of the object. Every differ- ent degree of light makes it have a different appearance, and total darkness takes away all appearance, but makes not the least change in the colour of the body. We may, by a variety of optical experiments, change the appear- ance of figure and magnitude in a body, as well as that of colour; we may make one body appear to be ten. But all men believe, that, as a multiplying glass does not really produce ten guineas out of one, nor a microscope turn a guinea into a ten-pound piece, so neither does a coloured glass change the real colour of the object seen through it, when it changes the appearance of that col- our. The common language of mankind shews evidently, that we ought to distinguish between the colour of a body, which is conceived to be a fixed and permanent quality in the body, and the appearance of that colour to the eye, which may be varied a thousand ways, by a variation of the light, of the medium, or of the eye it- self. The permanent colour of the body is the cause which, by the mediation of various kinds or degrees of light, and of various transparent bodies interposed, pro- duces all this variety of appearances. When a coloured body is presented, there is a certain apparition to the eye, or to the mind, which we have called the appearance of col- our. Mr. Locke calls it an idea; and, indeed, it may be called so with the greatest propriety. This idea can have no existence but when it is perceived. It is a kind of thought, and can only be the act of a percipient or thinking being. By the constitution of our nature, we are led to conceive this idea as a sign of something ex- ternal, and are impatient till we learn its meaning. A thousand experiments for this purpose are made every day by children, even before they come to the use of rea- SEC. IV.] THE PHILOSOPHY OF REID. 175 son. They look at things, they handle them, they put them in various positions, at different distances, and in different lights. The ideas of sight, by these means, come to be associated with, and readily to suggest, things external, and altogether unlike them. In particular, that idea which we have called the appearance of colour, suggests the conception and belief of some unknown quality in the body which occasions the idea; and it is to this quality, and not to the idea, that we give the name of colour. * The various colours, although in their nature equally unknown, are easily distinguished when we think or speak of them, by being associated with the ideas which they excite. In like manner, gravity, mag- netism, and electricity, although all unknown qualities, are distinguished by their different effects. As we grow up, the mind acquires a habit of passing so rapidly from the ideas of sight to the external things suggested by them, that the ideas are not in the least attended to, nor have they names given them in common language. When we think or speak of any particular colour, however simple the notion may seem to be which is pre- sented to the imagination, it is really in some sort com- pounded. It involves an unknown cause and a known effect. The name of colour belongs indeed to the cause only, and not to the effect. But as the cause is unknown, we can form no distinct conception of it but by its rela- tion to the known effect; and, therefore, both go together in the imagination, and are so closely united, that they are mistaken for one simple object of thought* When I * It is justly observed by Mr. Stewart, that these passages seem inconsistent with each other. If in the perception of colour, the sen- sation and the quality "be so closely united as to be mistaken for one simple object of thought," does it not obviously follow, that it is to this compounded notion the name of colour must in general be given ? On the other hand, when it is said that the name of colour is never given to the sensation, btit to the quality onfy, does not this imply, that every time the word is pronounced, the quality is sepa- rated from the sensation, even in the imagination of the vulgar ? H. 176 THE PHILOSOPHY OF REID. tCn.Vl. would conceive those colours of bodies which we call scar- let and blue if I conceived them only as unknown quali- ties, I could perceive no distinction between the one and the other. I must, therefore, for the sake of dis- tinction, join to each of them, in my imagination, some effect or some relation that is peculiar; and the most obvious distinction is, the appearance which one and the other makes to the eye. Hence the appearance is, in the imagination, so closely united with the quality called a scarlet-colour, that they are apt to be mistaken for one and the same thing, although they are in reality so differ- ent and 'so unlike, that one is an idea in the mind, and the other is a quality of body. I conclude, then, that colour is not a sensation, but a secondary quality of bodies, in the sense we have already explained; that it is a certain power or virtue in bodies, that in fair daylight exhibits to the eye an appearance which is very familiar to us, although it hath no name. Colour differs from other secondary qualities in this, that, whereas the name of the quality is sometimes given to the sensation which indicates it, and is occasioned by it, we never, as far as I can judge, give the name of col- our to the sensation, but to the quality only. * Perhaps the reason of this may be,, that the appearances of the same colour are so various and changeable, according to the different modifications of the light, of the medium, and of the eye, that language could not afford names for them. And, indeed, they are so little interesting that they are never attended to, but serve only as signs to in- troduce the things signified by them. Nor ought it to appear incredible, that appearances so frequent and so familiar should have no names, nor be made objects of thought; since we have before shewn that this is true of many sensations of touch, which are no less frequent nor less familiar. * See note on p. 175. SEC. V.] THE PHILOSOPHY OF REID. 177 Section V. AN INFERENCE .FROM THE PRECEDING. From what hath been said about colour, we may in- fer two things. The first is, that one of the most re- markable paradoxes of modern philosophy, which hath been universally esteemed as a great discovery, is, in reality, when examined to the bottom, nothing else but an abuse of words. The paradox I mean is, That col- our is not a quality of bodies, but only an idea in the mind. We have shewn, that the word colour, as used by the vulgar, cannot signify an idea in the mind, but a permanent quality of body. We have shewn that there is really a permanent quality of body, to which the common use of this word exactly agrees. Can any stronger proof be desired, that this quality is that to which the vulgar give the name of colour? If it should be said, that this quality, to which we give the name of colour, is unknown to the vulgar, and, therefore, can have no name among them, I answer, it is, indeed, known only by its effects that is, by its exciting a certain idea in us; but are there not numberless qualities of bodies which are known only by their effects, to which, notwithstanding, we find it necessary to give names ? Medicine alone might fur- nish us with a hundred instances of this kind. Do not the words astringent, narcotic, epispastic, caustic, and innu- merable others, signify qualities of bodies, which are known only by their effects upon animal bodies ? Why, then, should not the vulgar give a name to a quality, whose effects are every moment perceived by their eyes ? We have all the reason, therefore, that the nature of the thing admits, to think that the vulgar apply the name of colour to that quality of bodies which excites in us what the philosophers call the idea of colour. And that there is such a quality in bodies, all philosophers 178 THE PHILOSOPHY OF REID. [Cn. VI. allow, who allow that there is any such thing as body. Philosophers have thought fit to leave that quality of bodies which the vulgar call colour, without a name, and to give the name of colour to the idea or appearance, to which, as we have shewn, the vulgar give no name, be- cause they never make it an object of thought or reflec- tion. Hence it appears, that when philosophers affirm that colour is not in bodies, but in the mind, and the vulgar affirm that colour is not in the mind, but is a quality of bodies, there is no difference between them about things, but only about the meaning of a word. The vulgar have undoubted right to give names to things which they are daily conversant about; and phi- losophers seem justly chargeable with an abuse of lan- guage, when they change the meaning of a common word, without giving warning. If it is a good rule, to think with philosophers and speak with the vulgar, it must be right to speak with the vulgar when we think with them, and not to shock them by philosophical paradoxes, which, when put into com- mon language, express only the common sense of man- kind. If you ask a man that is no philosopher, what colour is, or what makes one body appear white, another scar- let, he cannot tell. He leaves that inquiry to philos- ophers, and can embrace any hypothesis about it, ex- cept that of our modern philosophers, who affirm that colour is not in body, but only in the mind. Nothing appears more shocking to his apprehension, than that visible objects should have no colour, and that colour should be in that which he conceives to be invisi- ble. Vet this strange paradox is not only universally re- ceived, but considered as one of the noblest discoveries of modern philosophy. The ingenious Addison, in the Spectator, No. 413, speaks thus of it: "I have here supposed that my reader is acquainted with that great modern discovery, which is at present universally ac- SEC.V.] THE PHILOSOPHY OF REID. 179 knowledged by all the inquirers into natural philoso- phy namely, that light and colours, as apprehended by the imagination, are only ideas in the mind, and not qualities that have any existence in matter. As this is a truth which has been proved incontestably by many modern philosophers, and is, indeed, one of the finest speculations in that science, if the English reader would see the notion explained at large, he may find it in the eighth chapter of the second book of Locke's Essay on Human Understanding.'" Mr. Locke and Mr. Addison are writers who have de- served so well of mankind, that one must feel some un- easiness in differing from them, and would wish to ascribe all the merit that is due to a discovery upon which they put so high a value. And, indeed, it is just to acknowledge that Locke, and other modern philoso- phers, on the subject of secondary qualities, have the merit of distinguishing more accurately than those that went before them, between the sensation in the mind, and that constitution or quality of bodies which gives occasion to the sensation. They have shewn clearly that these two things are not only distinct, but altogether unlike: that there is no similitude between the effluvia of an odorous body and the sensation of smell, or between the vibrations of a sounding body and the sensation of sound: that there can be no resemblance between the feeling of heat, and the constitution of the heated body which occasions it; or between the appearance which a coloured body makes to the eye, and the texture of the body which causes that appearance. Nor was the merit small of distinguishing these things accurately; because, however different and unlike in their nature, they have been always so associated in' the imagination, as to coalesce, as it were, into one two- faced form, which, from its amphibious nature, could not justly be appropriated either to body or mind; and, until it was properly distinguished into its different con- 180 THE PHILOSOPHY OF REID. [Cn. VI. stituent parts, it was impossible to assign to either their just shares in it. None of the ancient philosophers had made this distinction. * The followers of Democritus and Epicurus conceived the forms of heat, and sound, and colour, to be in the mind only; but that our senses fal- laciously represented them as being in bodies. The Peripatetics imagined that those forms are really in bodies; and that the images of them are conveyed to the mind by our senses, f The one system made the senses naturally fallacious and deceitful; the other made the qualities of body to resemble the sensations of the mind. Nor was it possi- ble to find a third, without making the distinction we have mentioned; by which, indeed, the errors of both these ancient systems are avoided, and we are not left under the hard necessity of believing^ either, on the one hand, that our sensations are like to the qualities of body, or, on the other, that God hath given us one faculty to deceive us, and another to detect the cheat. We desire, therefore, with pleasure, to do justice to the doctrine of Locke, and other modern philosophers, with regard to colour and other secondary qualities, and to ascribe to it its due merit, while we beg leave to cen- sure the language in which they have expressed their doctrine. When they had explained and established the distinction between the appearance which colour makes to the eye, and the modification of the coloured body which, by the laws of nature, causes that appearance, the question was, whether to give the name of colour to * This is inaccurate. The distinction was known to the ancient philosophers; and Democritus was generally allowed to be its author. This Reid himself elsewhere indeed admits. (See above, pp. 140 156, '57).-H. \ These statements concerning both classes of philosophers are vague and incorrect. The latter, in general, only allowed species for two senses, Sight and Hearing; few admitted them in Feeling; and some rejected them altogether. H. SEC. VI.J THE PHILOSOPHY OF REID. l8l the cause or to the effect ? By giving it, as they have done, to the effect, they set philosophy apparently in opposition to common sense, and expose it to the ridi- cule of the vulgar. But had they given the name of colour to the cause, as they ought to have done, they must then have affirmed, with the vulgar, that colour is a quality of bodies; and that there is neither colour nor anything like it in the mind. Their language, as well as their sentiments, would have been perfectly agreeable to the common apprehensions of mankind, and true Philosophy would have joined hands with Common Sense. As Locke was no enemy to common sense, it may be presumed, that, in this instance, as in some others, he was seduced by some received hypothesis; and that this was actually the case, will appear in the follow- ing section. Section VI. THAT NONE OF OUR SENSATIONS ARE RESEMBLANCES OF ANT OF THE QUALITIES OF BODIES. A second inference is, that, although colour is really a quality of body, yet it is not represented to the mind by an idea or sensation that resembles it; on the contrary, it is suggested by an idea which does not in the least resemble it. And this inference is applicable, not to colour only, but to all the qualities of body which we have examined. It deserves to be remarked, that, in the analysis we have hitherto given of the operations of the five senses, and of the qualities of bodies discovered by them, no in- stance hath occurred, either of any sensation which re- sembles any quality of body, or of any quality of body whose image or resemblance is conveyed to the mind by means of the senses. There is no phenomenon in nature more unaccounta- ble than the intercourse that is camacbSfiStfcfen the 0? THE niXTlBSXT 182 THE PHILOSOPHY OF REIDc [CH, VI. mind and the external world there is no phenomenon which philosophical spirits have shewn greater avidity to pry into, and to resolve. It is agreed by all, that this intercourse is carried on by means of the senses; and this satisfies the vulgar curiosity, but not the philosophic. Philosophers must have some system, some hypothesis, that shews the manner in which our senses make us acquainted with external things. All the fertility of human invention seems to have produced only one hy- pothesis for this purpose, which, therefore, hath been universally received; and that is, that the mind, like a mirror, receives the images of things from without, by means of the senses: so that their use must be to con- vey these images into the mind. * Whether to these images of external things in the mind, we give the name of sensible forms, or sensible species, with the Peripatetics, or the name of ideas of sen- sation, with Locke; or whether, with later philosophers, we distinguish sensations, which are immediately conveyed by the senses, from ideas of sensation, which are faint copies of our sensations retained in the> memory and im- agination ; f these are only differences about words. The hypothesis I have mentioned is common to all these different systems. The necessary and allowed consequence of this hypoth- esis is, that no material thing, nor any quality of material things, can be conceived by us, or made an object of thought, until its image is conveyed to the mind by means of the senses. We shall examine this hypothesis particularly afterwards, and at this time only observe, that, in consequence * This is incorrect, especially as it asserts that the one universal hypothesis of philosophy was, that "the mind receives the images of things from without," meaning by these images, immediate or rep- resentative objects, different from the modifications of the thinking subject itself. H. f He refers to Hume; Aristotle, however, and Hobbes, had pre- viously called Imagination a decaying sense. H. SEC. VI.] THE PHILOSOPHY OF REID. 183 of it, one would naturally expect, that to every quality and attribute of body we know or can conceive, there should be a sensation corresponding, which is the image and resemblance of that quality; and that the sensations which have no similitude or resemblance to body, or to any of its qualities, should give us no conception of a material world, or of anything belonging to it These things might be expected as the natural consequences of the hypothesis we have mentioned. Now, we have considered, in this and the preceding chapters, Extension, Figure, Solidity, Motion, Hardness, Roughness, as well as Colour, Heat, and Cold, Sound, Taste, and Smell. We have endeavoured to shew that our nature and constitution lead us to conceive these as qualities of body, as all mankind have always conceived them to be. We have likewise examined with great at- tention the various sensations we have by means of the five senses, and are not able to find among them all one single image of body, or of any of its qualities. From whence, then, come those images of body and of its qual- ities into the mind,? Let philosophers resolve this ques- tion. All I can say is, that they come not by the senses. I am sure that, by proper attention and care, I may know my sensations, and be able to affirm with certainty what they resemble, and what they do not resemble. I have examined them one by one, and compared them with matter and its qualities; and I cannot find one of them that confesses a resembling feature. A truth so evident as this that our sensations are not images of matter, or of any of its qualities ought not to yield to a hypothesis such as that above-mentioned, how- ever ancient, or however universally received by philos- ophers ; nor can there be any amicable union between the two. This will appear by some reflections upon the spirit of the ancient and modern philosophy concerning sensation. During the reign of the Peripatetic philosophy, our 1 84 THE PHILOSOPHY OF REID. [CH. VI. sensations were not minutely or accurately examined. The attention of philosophers, as well as of the vulgar, was turned to the things signified by them: therefore, in consequence of the common hypothesis, it was taken for granted, that all the sensations we have from external things, are the forms or images of these external things. And thus the truth we have mentioned yielded entirely to the hypothesis, and was altogether suppressed by it. Des Cartes gave a noble example of turning our attention inward, and scrutinizing our sensations; and this example hath been very worthily followed by modern philosophers, particularly by Malebranche, Locke, Berke- ley, and Hume. The effect of this scrutiny hath been, a gradual discovery of the truth above-mentioned to wit, the dissimilitude between the sensations of our minds, and the qualities or attributes of an insentient inert sub- stance, such as we conceive matter to be. But this valuable and useful discovery, in its different stages, hath still been unhappily united to the ancient hypothesis and from this inauspicious match of opinions, so un- friendly and discordant in their natures, have arisen those monsters of paradox and scepticism with which the modern philosophy is too justly chargeable. Locke saw clearly, and proved incontestably, that the sensations we have by taste, smell, and hearing, as well as the sensations of colour, heat, and cold, are not resemblances of anything in bodies; and in this he agrees with Des Cartes and Malebranche. Joining this opinion with the hypothesis, it follows necessarily, that three senses of the five are cut off from giving us any intelligence of the material world, as being altogether inept for that office. Smell, and taste, and sound, as well as colour and heat, can have no more relation to body, than anger or gratitude ; nor ought the former to be called qualities of body, whether primary or secondary, any more than the latter. For it was natural and obvious to argue thus from that hypothesis: If heat, and colour, and sound SEC. VI.] THE PHILOSOPHY OF REID. 185 are real qualities of body, the sensations by which we perceive them must be resemblances of those qualities ; but these sensations are not resemblances ; therefore, those are not real qualities of body. We see, then, that Locke, having found that the ideas of secondary qualities are no resemblances, was com- pelled, by a hypothesis common to all philosophers, to deny that they are real qualities of body. It is more difficult to assign a reason why, after this, he should call them secondary qualities; for this name, if I mistake not, was of his invention.* Surely he did not mean that they were secondary qualities of the mind ; and I do not see with what propriety, or even by what tolerable license, he could call them secondary qualities of body, after finding that they were no qualities of body at all. In this, he seems to have sacrificed to Common Sense, and to have been led by her authority even in opposition to his hypothesis. The same sovereign mistress of our opinions that led this philosopher to call those things secondary qualities of body, which, according to his principles and reasonings, were no qualities of body at all, hath led, not the vulgar of all ages only, but philoso- phers also, and even the disciples of Locke, to believe them to be real qualities of body she hath led them to investigate, by experiments, the nature of colour, and sound, and heat, in bodies. Nor hath this investigation been fruitless, as it must have been if there had been no such thing in bodies ; on the contrary, it hath produced very noble and useful discoveries, which make a very considerable part of natural philosophy. If, then, natural philosophy be not a dream, there is something in bodies which we call colour, and heat, and sound. And if this * The terms First and Second^ or Primary and Secondary qualities, were no more an invention of Locke than the distinction which he applied them to denote. The terms First and Second Qualities, as I have noticed, in the Aristotelian philosophy, marked out, however, a different distribution of qualities than that in question. H. 1 86 THE PHILOSOPHY OF REID. [Cn. VI. be so, the hypothesis from which the contrary is con- cluded, must be false : for the argument, leading to a false conclusion, recoils against the hypothesis from which it was drawn, and thus directs its force backward. If the qualities of body were known to us only by sensations that resemble them, then colour, and sound, and heat could be no qualities of body; but these are real qualities of body ; and, therefore, the qualities of body are not known only by means of sensations that resemble them. But to proceed. What Locke had proved with regard to the sensations we have by smell, taste, and hearing, Bishop Berkeley proved no less unanswerably with regard to all our other sensations ; to wit, that none of them can in the least resemble the qualities of a lifeless and insentient being, such as matter is conceived to be. Mr. Hume hath confirmed this by his authority and reasoning. This opinion surely looks with a very malign aspect upon the old hypothesis ; yet that hypothesis hath still been retained, and conjoined with it. And what a brood of monsters hath this produced ! The first-born of this union, and, perhaps, the most harmless, was, that the secondary qualities of body were mere sensations of the mind. To pass by Malebranche's notion of seeing all things in the ideas of the divine mind, as a foreigner, never naturalized in this island ; the next was Berkeley's system, That extension, and figure, and hardness, and motion that land, and sea, and houses, and our own bodies, as well as those of our wives, and children, and friends are nothing but ideas of the mind: and that there is nothing existing in nature, but minds and ideas. The progeny that followed, is still more frightful ; so that it is surprising, that one could be found who had the courage to act the midwife, to rear it up, and to usher it into the world. No causes nor effects ; no sub- stances, material or spiritual ; no evidence, even in SEC. VII.] THE PHILOSOPHY OF REID. 187 mathematical demonstration ; no liberty nor active power ; nothing existing in nature, but impressions and ideas following each other, without time, place, or subject. Surely no age ever produced such a system of opinions, justly deduced with great acuteness, perspicuity, and ele- gance, from a principle universally received. The hy- pothesis we have mentioned is the father of them all. The dissimilitude of our sensations and feelings to ex- ternal things, is the innocent mother of most of them. As it happens sometimes, in an arithmetical operation, that two errors balance one another, so that the con- clusion is little or nothing affected by them; but when one of them is corrected, and the other left, we are led farther from the truth than by both together: so it seems to have happened in the Peripatetic philosophy of sensation, compared with the modern. The Peripatetics adopted two errors; but the last served as a corrective to the first, and rendered it mild and gentle ; so that their system had no tendency to scepticism. The moderns have retained the first of those errors, but have gradually detected and corrected the last. The consequence hath been, that the light we have struck out hath created darkness, and scepticism hath advanced hand in hand with knowledge, spreading its melancholy gloom, first over the material worjd, and at last over the whole face of nature. Such a phenomenon as this, is apt to stagger even the lovers of light and knowledge, while its cause is latent ; but, when that is detected, it may give hopes that this darkness shall not be everlasting, but that it shall be succeeded by a more permanent light. Section VIL OF VISIBLE FIGURE AND EXTENSION. Although there is no resemblance, nor, as far as we know, any necessary connection, between that quality in a body which we call its colour, and the appearance which 1 88 THE PHILOSOPHY OF REID. [CH. VI that colour makes to the eye, it is quite otherwise with regard to its figure and magnitude. There is certainly a resemblance, and a necessary connection, between the visible figure and magnitude of a body, and its real figure and magnitude ; no man can give a reason why a scarlet colour affects the eye in the manner it does ; no man can be sure that it affects his eye in the same manner as it affects the eye of another, and that it has the same ap- pearance to him as it has to another man ; but we can assign a reason why a circle placed obliquely to the eye, should appear in the form of an ellipse. The visible figure, magnitude, and position may, by mathematical reasoning, be deduced from the real ; and it may be demonstrated, that every eye that sees distinctly and per- fectly, must, in the same situation, see it under this form, and no other. Nay, we may venture to affirm, that a man born blind, if he were instructed in mathematics, would be able to determine the visible figure of a body when its real figure, distance, and position, are given. Dr. Saunderson understood the projection of the sphere, and perspective. Now, I require no more knowledge in a blind man, in order to his being able to determine the visible figure of bodies, than that he can project the out- line of a given body, upon the surface of a hollow sphere, whose centre is in the eye. This projection is the visible figure he wants : for it is the same figure with that which is projected upon the tunica retina in vision. A blind man can conceive lines drawn from every point of the object to the centre of the eye, making an- gles. He can conceive that the length of the object will appear greater or less, in proportion to the angle which it subtends at the eye ; and that, in like manner, the breadth, and in general the distance, of any one point of the object from any other point, will appear greater or less, in proportion to the angles which those distances subtend. He can easily be made to conceive, that the visible appearance has no thickness, any more than a SEC. VII.] THE PHILOSOPHY OF REID. 189 projection of the sphere, or a perspective draught. He may be informed, that the eye, until it is aided by ex- perience, does not represent one object as nearer or more remote than another. Indeed, he would probably con- jecture this of himself, and be apt to think that the rays of light must make the same impression upon the eye, whether they come from a greater or a less distance. These are all the principles which we suppose our blind mathematician to have ; and these he may cer- tainly acquire by information and reflection. It is no less certain, that, from these principles, having given the real figure and magnitude of a body, and its position and distance with regard to the eye, he can find out its visible figure and magnitude. He can demonstrate in general, from these principles, that the visible figure of all bodies will be the same with that of their projection upon the surface of a hollow sphere, when the eye is placed in the centre. And he can demonstrate that their visible magnitude will be greater or less, according as their projection occupies a greater or less part of the surface of this sphere. To set this matter in another light, let us distinguish betwixt the position of objects with regard to the eye, and their distance from it. Objects that lie in the same right line drawn from the centre of the eye, have the same position, however different their distances from the eye may be : but objects which lie in different right lines drawn from the eye's centre, have a different position ; and this difference of position is greater or less in pro- portion to the angle made at the eye by the right lines mentioned. Having thus defined what we mean by the position of objects with regard to the eye, it is evident that, as the real figure of a body consists in the situation of its several parts with regard to one another, so its vis- ible figure consists in the position of its several parts with regard to the eye ; and, as he that hath a distinct conception of the situation of the parts of the body with 190 THE PHILOSOPHY OF REID. [Cn. VI. regard to one another, must have a distinct conception of its real figure ; so he that conceives distinctly the position of its several parts with regard to the eye, must have a distinct conception of its visible figure. Now, there is nothing, surely, to hinder a blind man from conceiving the position of the several parts of a body with regard to the eye, any more than from conceiving their situation with regard to one another ; and, there- fore, I conclude, that a blind man may attain a distinct conception of the visible figure of bodies. Although we think the arguments that have been offered are sufficient to prove that a blind man may con- ceive the visible extension and figure of bodies ; yet, in order to remove some prejudices against this truth, it will be of use to compare the notion which a blind mathematician might form to himself of visible figure, with that which is presented to the eye in vision, and to observe wherein they differ. First, Visible figure is never presented to the eye but in conjunction with colour : and, although there be no connection between them from the nature of the things, yet, having so invariably kept company together, we are hardly able to disjoin them even in our imagination. What mightily increases this difficulty is, that we have never been accustomed to make visible figure an object of thought. It is only used as a sign, and, having served this purpose, passes away, without leaving a trace behind. The drawer or designer, whose business it is to hunt this fugitive form, and to take a copy of it, finds how difficult his task is, after many years' labour and practice. Happy ! if at last he can acquire the art of arresting it in his imagination, until he can delineate it. For then it is evident that he must be able to draw as accurately from the life as from a copy. But how few of the professed masters of designing are ever able to arrive at this degree of perfection ! It is no wonder, then, that we should find so great difficulty in conceiving SBC. VII.] THE PHILOSOPHY OF REID. 191 this form apart from its constant associate, when it is so difficult to conceive it at all. But our blind man's no- tion of visible figure will not be associated with colour, of which he hath no conception, but it will, perhaps, be associated with hardness or smoothness, with which he is acquainted by touch. These different associations are apt to impose upon us, and to make things seem different, which, in reality, are the same. Secondly, The blind man forms the notion of visible figure to himself, by thought, and by mathematical reasoning from principles ; whereas, the man that sees, has it presented to his eye at once, without any labour, without any reasoning, by a kind of inspiration. A man may form to himself the notion of a parabola, or a cycloid, from the mathematical definition of those figures, although he had never seen them drawn or de- lineated. Another, who knows nothing of the mathe- matical definition of the figures, may see them delineated on paper, or feel them cut out in wood. Each may have a distinct conception of the figures, one by mathematical reasoning, the other by sense. Now, the blind man forms his notion of visible figure in the same manner as the first of these formed his notion of a parabola or a cycloid, which he never saw. Thirdly, Visible figure leads the man that sees, directly to the conception of the real figure, of which it is a sign. But the blind man's thoughts move in a contrary direc- tion. For he must first know the real figure, distance, and situation of the body, and from thence he slowly traces out the visible figure by mathematical reasoning. Nor does his nature lead him to conceive this visible figure as a sign ; it is a creature of his own reason and imagination. Ip2 THE PHILOSOPHY OF REID. [Cn. VI. Section VIIL SOME QUERIES CONCERNING VISIBLE FIGURE ANSWERED. It may be asked, What kind of thing is this visible figure ? Is it a Sensation, or an Idea ? If it is an idea, from what sensation is it copied ? These questions may seem trivial or impertinent to one who does not know that there is a tribunal of inquisition erected by certain modern philosophers, before which everything in nature must answer. The articles of inquisition are few indeed, but very dreadful in their consequences. They are only these : Is the prisoner an Impression or an Idea ? If an idea, from what impression copied ? Now, if it appears that the prisoner is neither an impression, nor an idea copied from some impression, immediately, without being allowed to offer anything in arrest of judgment, he is sentenced to pass out of existence, and to be, in all time to come, an empty unmeaning sound, or the ghost of a departed entity. Before this dreadful tribunal, cause and effect, time and place, matter and spirit, have been tried and cast : how then shall such a poor flimsy form as visible figure stand before it ? It must even plead guilty, and confess that it is neither an impression nor an idea. For, alas ! it is notorious, that it is extended in length and breadth ; it may be long or short, broad or narrow, triangular, quadrangular, or circular; and, therefore, unless ideas and impressions are extended and figured, it cannot belong to that category. If it should still be asked, To what category of beings does visible figure then belong ? I can only, in answer, give some tokens, by which those who are better ac- quainted with the categories, may chance to find its place. It is, as we have said, the position of the several parts of a figured body with regard to the eye. The SEC. VIII.] THE PHILOSOPHY OF REID. 193 different positions of the several parts of the body with regard to the eye, when put together, make a real figure, which is truly extended in length and breadth, and which represents a figure that is extended in length, breadth, and thickness. In like manner, a projection of the sphere is a real figure, and hath length and breadth, but represents the sphere, which hath three dimensions. A projection of the sphere, or a perspec- tive view of a palace, is a representative in the very same sense as visible figure is ; and wherever they have their lodgings in the categories, this will be found to dwell next door to them. It may farther be asked, Whether there be any sensa- tion proper to visible figure, by which it is suggested in vision ? or by what means it is presented to the mind ? This is a question of some importance, in order to our having a distinct notion of the faculty of seeing : and to give all the light to it we can, it is necessary to compare this sense with other senses, and to make some supposi- tions, by which we may be enabled to distinguish things that are apt to be confounded, although they are totally different. There are three of our senses which give us intelli- gence of things at a distance: smell, hearing, and sight. In smelling and in hearing, we have a sensation or im- pression upon the mind, which, by our constitution, we conceive to be a sign of something external : but the po- sition of this external thing, with regard to the organ of sense, is not presented to the mind along with the sen- sation. When I hear the sound of a coach, I could not, previous to experience, determine whether the sounding body was above or below, to the right hand or to the left. So that the sensation suggests to me some external object as the cause or occasion of it; but it suggests not the position of that object, whether it lies in this direc- tion or in that. The same thing may be said with regard to smelling. But the case is quite different with regard 194 THE PHILOSOPHY OF REID. [Cn. VI. to seeing. When I see an object, the appearance which the colour of it makes, may be called the sensation, which suggests to me some external thing as its cause; but it suggests likewise the individual direction and position of this cause with regard to the eye. I know it is precisely in such a direction, and in no other. At the same time, I am not conscious of anything that can be called sensa- tion, but the sensation of colour. The position of the coloured thing is no sensation; but it is by the laws of my constitution presented to the mind along with the colour, without any additional sensation. Let us suppose that the eye were so constituted that the rays coming from any one point of the object were not, as they are in our eyes, collected in one point of the retina,\)ut diffused over the whole: it is evident to those who understand the structure of the eye, that such an eye as we have supposed, would shew the colour of a body as our eyes do, but that it would neither shew figure nor position. The operation of such an eye would be precisely similar to that of hearing and smell; it would give no perception of figure or extension, but merely of colour. Nor is the supposition we have made altogether imaginary: for it is nearly the case of most people who have cataracts, whose crystalline, as Mr. Cheselden ob- serves, does not altogether exclude the rays of light, but diffuses them over the retina, so that such persons see things as one does through a glass of broken gelly: they perceive the colour, but nothing of the figure or magni- tude of objects. Again, if we should suppose that smell and sound were conveyed in right lines from the objects, and that every sensation of hearing and smell suggested the pre- cise direction or position of its object; in this case, the operations of hearing and smelling would be similar to that of seeing: we should smell and hear the figure of objects, in the same sense as now we see it; and every smell and sound would be associated with some SEC. VIII.] THE PHILOSOPHY OF REID. 19$ figure in the imagination, as colour is in our present state. We have reason to believe, that the rays of light make some impression upon the retina; but we are not con- scious of this impression; nor have anatomists or philos- ophers been able to discover the nature and effects of it; whether it produces a vibration in the nerve, or the mo- tion of some subtile fluid contained in the nerve, or something different from either, to which we cannot give a name. Whatever it is, we shall call it the material im- pression ; remembering carefully, that it is not an impres- sion upon the mind, but upon the body; and that it is no sensation, nor can resemble sensation, any more than figure or motion can resemble thought. Now, this ma- terial impression, made upon a particular point of the retina, by the laws of our constitution, suggests two things to the mind namely, the colour an i the position of some external object. No man can give a reason why the same material impression might not have suggested sound, or smell, or either of these, along with the posi- tion of the object. That it should suggest colour and position, and nothing else, we can resolve only into our constitution, or the will of our Maker. And since there is no necessary connection between these two things sug- gested by this material impression, it might, if it had so pleased our Creator, have suggested one of them without the other. Let us suppose, therefore, since it plainly appears to be possible, that our eyes had been so framed as to suggest to us the position of the object, without suggesting colour, or any other quality: What is the con- sequence of this supposition ? It is evidently this, that the person endued with such an eye, would perceive the visible figure of bodies, without having any sensation or impression made upon his mind. The figure he per- ceives is altogether external; and therefore cannot be called an impression upon the mind, without the gross- est abuse of language. If it should be said, that it is 196 THE PHILOSOPHY OF REID. [Cu. VI. impossible to perceive a figure, unless there be some im- pression of it upon the mind, I beg leave not to admit the impossibility of this without some proof: and I can find none. Neither can I conceive what is meant by an impression of figure upon the mind. I can conceive an impression of figure upon wax, or upon any body that is fit to receive it; but an impression of it upon the mind, is to me quite unintelligible; and, although I form the most distinct conception of the figure, I cannot, upon the strictest examination, find any impression of it upon my mind. If we suppose, last of all, that the eye hath the power restored of perceiving colour, I apprehend that it will be allowed, that now it perceives figure in the very same manner as before, with this difference only, that colour is always joined with it. In answer, therefore, to the question proposed, there seems to be no sensation that is appropriated to visible figure, or whose office it is to suggest it. It seems to be suggested immediately by the material impression upon the organ, of which we are not conscious: and why may not a material impression upon the retina suggest visible figure, as well as the material impression made upon the hand, when we grasp a ball, suggests real figure ? In the one case, one and the same material impression, suggests both colour and visible figure; and in the other case, one and the same material impression suggests hard- ness, heat, or cold, and real figure, all at the same time. We shall conclude this section with another question upon this subject. Since the visible figure of bodies is a real and external object to the eye, as their tangible fig- ure is to the touch, it may be asked, Whence arises the difficulty of attending to the first, and the facility of at- tending to the last ? It is certain that the first is more frequently presented to the eye, than the last is to the touch; the first is as distinct and determinate an object SEC. VIII.) THE PHILOSOPHY OF REID. 197 as the last, and seems in its own nature as proper for speculation. Yet so little hath it been attended to, that it never had a name in any language, until Bishop Berke- ley gave it that which we have used after his example, to distinguish it from the figure which is the object of touch. The difficulty of attending to the visible figure of bodies, and making it an object of thought, appears so similar to that which we find in attending to our sensa- tions, that both have probably like causes. Nature in- tended the visible figure as a sign of the tangible figure and situation of bodies, and hath taught us, by a kind of instinct, to put it always to this use. Hence it hap- pens, that the mind passes over it with a rapid motion, to attend to the things signified by it. It is as unnatu- ral to the mind to stop at the visible figure, and attend to it, as it is to a spherical body to stop upon an inclined plane. There is an inward principle, which constantly carries it forward, and which cannot be overcome but by a contrary force. There are other external things which nature intended for signs; and we find this common to them all, that the mind is disposed to overlook them, and to attend only to the things signified by them. Thus there are certain modifications of the human face, which are natural signs of the present disposition of the mind. Every man un- derstands the meaning of these signs, but not one of a hun- dred ever attended to the signs themselves, or knows anything about them. Hence you may find many an ex- cellent practical physiognomist who knows nothing of the proportions of a face nor can delineate or describe the expression of any one passion. An excellent painter or statuary can tell, not only what are the proportions of a good face, but what changes every passion makes in it. This, however, is one of the chief mysteries of his art, to the acquisition of which in- finite labour and attention, as well as a happy genius, 198 THE PHILOSOPHY OF REID. (Cn. VI. are required ; but when he puts his art in practice, and happily expresses a passion by its proper signs, every one understands the meaning of these signs, without art, and without reflection. What has been said of painting, might easily be ap- plied to all the fine arts. The difficulty in them all con- sists in knowing and attending to those natural signs whereof every man understands the meaning. We pass from the sign to the thing signified, with ease, and by natural impulse ; but to go backward from the thing signified to the sign, is a work of labour and diffi- culty. Visible figure, therefore, being intended by nature to be a sign, we pass on immediately to the thing signi- fied, and cannot easily return to give any attention to the sign. Nothing shews more clearly our indisposition to at- tend to visible figure and visible extension than this that, although mathematical reasoning is no less appli- cable to them, than to tangible figure and extension, yet they have entirely escaped the notice of mathematicians. While that figure and that extension which are objects of touch, have been tortured ten thousand ways for twenty centuries, and a very noble system of science has been drawn out of them, not a single proposition do we find with regard to the figure and extension which are the immediate objects of sight ! When the geometrician draws a diagram with the most perfect accuracy when he keeps his eye fixed upon it, while he goes through a long process of reasoning, and demonstrates the relations of the several parts of his fig- ure he does not consider that the visible figure pre- sented to his eye, is only the representative of a tangible figure, upon which all his attention is fixed ; he does not consider that these two figures have really different pro- perties ; and that, what he demonstrates to be true of the one, is not true of the other. This, perhaps, will seem so great a paradox, even to SEC. IX.] THE PHILOSOPHY OF REID. 199 mathematicians, as to require demonstration before it can be believed. Nor is the demonstration at all difiV cult, if the reader will have patience to enter but a little into the mathematical consideration of visible figure, which we shall call the geometry ofvisibles. Section IX. OF THE GEOMETRY OF VISIBLES.* In this geometry, the definitions of a point ; of a line, whether straight or curve ; of an angle, whether acute, or right, or obtuse; and of a circle are the same as in common geometry. The mathematical reader will easily enter into the whole mystery of this geometry, if he at- tends duly to these few evident principles. 1. Supposing the eye placed in the centre of a sphere, every great circle of the sphere will have the same ap- pearance to the eye as if it was a straight line ; for the curvature of the circle being turned directly toward the eye, is not perceived by it. And, for the same reason, any line which is drawn in the plane of a great circle of the sphere, whether it be in reality straight or curve, will appear straight to the eye. 2. Every visible right line will appear to coincide with some great circle of the sphere ; and the circumference of that great circle, even when it is produced until it returns into itself, will appear to be a continuation of the same visible right line, all the parts of it being visi- bly in directum. For the eye, perceiving only the posi- tion of objects with regard to itself, and not their dis- tance, will see those points in the same visible place which have the same position with regard to the eye, * How does this differ from a doctrine of Perspective ? At any rate, the notion is Berkeley's. Compare "New Theory of Vision," 200 THE PHILOSOPHY OF REID. [Cn. VI. how different soever their distances from it may be. Now, since a plane passing through the eye and a given visible right line, will be the plane of some great circle of the sphere, every point of the visible right line will have the same position as some point of the great circle; therefore, they will both have the same visible place, and coincide to the eye ; and the whole circumference of the great circle, continued even until it returns into itself, will appear to be a continuation of the same visible right line. Hence it follows 3. That every visible right line, when it is continued in directum, as far as it may be continued, will be rep- resented by a great circle of a sphere, in whose centre the eye is placed. It follows 4. That the visible angle comprehended under two visible right lines, is equal to the spherical angle com- prehended under the two great circles, which are the representatives of these visible lines. For, since the vis- ible lines appear to coincide with the great circles, the visible angle comprehended under the former must be equal to the visible angle comprehended under the latter. But the visible angle comprehended under the two great circles, when seen from the centre, is of the same mag- nitude with the spherical angle which they really com- prehend, as mathematicians know ; therefore, the visi- ble angle made by any two visible lines is equal to the spherical angle made by the two great circles of the sphere which are their representatives. 5. Hence it is evident, that every visible right-lined triangle will coincide in all its parts with some spherical triangle. The sides of the one will appear equal to the sides of the other, and the angles of the one to the an- gles of the other, each to each : and, therefore, the whole of the one triangle will appear equal to the whole of the other. In a word, to the eye they will be one and the same, and have the same mathematical properties. The SEC. IX.) THE PHILOSOPHY OF REID. 2OI properties, therefore, of visible right-lined triangles are not the same with the properties of plain triangles, but are the same with those of spherical triangles. 6. Every lesser circle of the sphere will appear a cir- cle to the eye, placed, as we have supposed all along, in the centre of the sphere ; and, on the other hand, every visible circle will appear to coincide with some lesser cir- cle of the sphere. 7. Moreover, the whole surface of the sphere will rep- resent the whole of visible space ; for, since every visible point coincides with some point of the surface of the sphere, and has the same visible place, it follows, that all the parts of the spherical surface taken together, will represent all possible visible places that is, the whole of visible space. And from this it follows, in the last place 8. That every visible figure will be represented by that part of the surface of the sphere on which it might be projected, the eye being in the centre. And every such visible figure will bear the same ratio to the whole of visi- ble space, as the part of the spherical surface which rep- resents it, bears to the whole spherical surface. The mathematical reader, I hope, will enter into these principles with perfect facility, and will as easily per- ceive that the following propositions with regard to visi- ble figure and space, which we offer only as a specimen, may be mathematically demonstrated from them, and are not less true nor less evident than the propositions of Euclid, with regard to tangible figures. Prop. i. Every right line being produced, will at last return into itself. 2. A right line returning into itself, is the longest possible right line ; and all other right lines bear a finite ratio to it. 3. A right line returning into itself, divides the whole of visible space into two equal parts, which will both be comprehended under this right line. 202 THE PHILOSOPHY OF REID. (Ca. VI. 4. The whole of visible space bears a finite ratio to any part of it. 5. Any two right lines being produced, will meet in two points, and mutually bisect each other. 6. If two lines be parallel that is, everywhere equally distant from each other they cannot both be straight. 7. Any right line being given, a point may be found, which is at the same distance from all the points of the given right line. 8. A circle may be parallel to a right line that is, may be equally distant from it in all its parts. 9. Right-lined triangles that are similar, are also equal. 10. Of every right-lined triangle, the three angles taken together, are greater than two right angles. 11. The angles of a right-lined [triangle, may all be right angles, or all obtuse angles. 12. Unequal circles are not as the squares of their diameters, nor are their circumferences in the ratio of their diameters. This small specimen of the geometry of visibles, is in- tended to lead the reader to a clear and distinct con- ception of the figure and extension which is presented to the mind by vision ; and to demonstrate the truth of what we have affirmed above namely, that those figures and that extension which are the immediate objects of sight, are not the figures and the extension about which common geometry is employed ; that the geometrician, while he looks at his diagram, and demonstrates a proposition, hath a figure presented to his eye, which is only a sign and representative of a tangible figure : that he gives not the least attention to the first, but attends only to the last ; and that these two figures have differ- ent properties, so that what he demonstrates of the one, is not true of the other. It deserves, however, to be remarked, that, as a small part of a spherical surface differs not sensibly from a SEC. IX. THE PHILOSOPHY OF REIt). 2O3 plain surface, so a small part of visible extension differs very little from that extension in length and breadth, which is the object of touch. And it is likewise to be ob- served, that the human eye is so formed, that an object which is seen distinctly and at one view, can occupy but a small part of visible space ; for we never see distinctly what is at a considerable distance from the axis of the eye ; and, therefore, when we would see a large object at one view, the eye must be at so great a distance, that the object occupies but a small part of visible space. From these two observations, it follows, that plain fig- ures which are seen at one view, when their planes are not oblique, but direct to the eye, differ little from the visible figures which they present to the eye. The sev- eral lines in the tangible figure, have very nearly the same proportion to each other as in the visible ; and the an- gles of the one are very nearly, although not strictly and mathematically, equal to those of the other. Although, therefore, we have found many instances of natural signs which have no similitude to the things signified, this is not the case with regard to visible figure. It hath, in all cases, such a similitude to the thing signified by it, as a plan or profile hath to that which it represents ; and, in some cases, the sign and thing signified have to all sense the same figure and the same proportions. If we could find a being endued with sight only, without any other external sense, and capable of reflecting and reasoning upon what he sees, the notions and philoso- phical speculations of such a being, might assist us in the difficult task of distinguishing the perceptions which we have purely by sight, from those which derive their origin from other senses. Let us suppose such a being, and conceive, as well as we can, what notion he would have of visible objects, and what conclusions he would deduce from them. We must not conceive him dis- posed by his constitution, as we are, to consider the visible appearance as a sign of something else : it is no 204 THE PHILOSOPHY OF REID. |CH. VI. sign to him, because there is nothing signified by it ; and, therefore, we must suppose him as much disposed to at- tend to the visible figure and extension of bodies, as we are disposed to attend to their tangible figure and ex- tension. If various figures were presented to his sense, he might, without doubt, as they grow familiar, compare them together, and perceive wherein they agree, and wherein they differ. He might perceive visible objects to have length and breadth, but could have no notion of a third dimension, any more than we can have of a fourth. All visible objects would appear to be terminated by lines, straight or curve; and objects terminated by the same visible lines, would occupy the same place, and fill the same part of visible space. It would not be possible for him to conceive one object to be be- hind another, or one to be nearer, another more dis- tant. To us, who conceive three dimensions, a line may be conceived straight; or it may be conceived incurvated in one dimension, and straight in another; or, lastly, it may be incurvated in two dimensions. Suppose a line to be drawn upwards and downwards, its length makes one dimension, which we shall call upwards and downwards; and there are two dimensions remaining, according to which it may be straight or curve. It may be bent to the right or to the left, and, if it has no bending either to right or left, it is straight in this dimension. But supposing it straight in this dimension of right and left, there is still another dimension remaining, in which it may be curve; for it may be bent backwards or forwards. When we conceive a tangible straight line, we exclude curvature in either of these two dimensions: and as what is conceived to be excluded, must be conceived, as well as what is conceived to be included, it follows that all the three dimensions enter into our conception of a straight line. Its length is one dimension, its straightnessintwo SfiC. IX.) THE PHILOSOPHY OF REID. 205 other dimensions is included, or curvature in these two dimensions excluded, in the conception of it. The being we have supposed, having no conception of more than two dimensions, of which the length of a line is one, cannot possibly conceive it either straight or curve in more than one dimension; so that, in his con- ception of a right line, curvature to the right hand or left is excluded; but curvature backwards or forwards cannot be excluded, because he neither hath, nor can have any conception of such curvature. Hence we see the reason that a line which is straight to the eye, may return into itself; for its being straight to the eye, implies only straightness in one dimension; and a line which is straight in one dimension may, notwithstanding, be curve in another dimension, and so may return into it- self. To us, who conceive three dimensions, a surface is that which hath length and breadth, excluding thickness; and a surface may be either plain in this third dimension, or it may be incurvated: so that the notion of a third dimension enters into our conception of a surface; for it is only by means of this third dimension that we can distinguish surfaces into plain and curve surfaces; and neither one nor the other can be conceived without con- ceiving a third dimension. The being we have supposed, having no conception of a third dimension, his visible figures have length and breadth indeed; but thickness is neither included nor ex- cluded, being a thing of which he has no conception. And, therefore, visible figures, although they have length and breadth, as surfaces have, yet they are neither plain surfaces nor curve surfaces. For a curve surface implies curvature in a third dimension, and a plain surface im- plies the want of curvature in a third dimension; and such a being can conceive neither of these, because he has no conception of a third dimension. Moreover, al- though he hath a distinct conception of the inclination 206 THE PHILOSOPHY OF REID. [Cn. VI. of two lines which make an angle, yet he can neither conceive "a plain angle nor a spherical angle. Even his notion of a point is somewhat less determined than ours. In the notion of a point, we exclude length, breadth, and thickness; he excludes length and breadth, but cannot either exclude, or include thickness, because he hath no conception of it. Having thus settled the notions which such a being as we have supposed might form of mathematical points, lines, angles, and figures, it is easy to see, that, by com- paring these together, and reasoning about them, he might discover their relations, and form geometrical conclusions built upon self-evident principles. He might likewise, without doubt, have the same notions of numbers as we have, and form a system of arithmetic. It is not material to say in what order he might proceed in such discoveries, or how much time and pains he might employ about them, but what such a being, by rea- son and ingenuity, without any materials of sensation but those of sight only, might discover. As it is more difficult to attend to a detail of possibilities than of facts, even of slender authority, I shall beg leave to give an extract from the travels of Johannes Rudolphus Anepigraphus, a Rosicrucian philosopher, who having, by deep study of the occult sciences, acquired the art of transporting himself to various sublunary regions, and of conversing with various orders of intelligences, in the course of his adventures became acquainted with an or- der of beings exactly such as I have supposed. How they communicate their sentiments to one an- other, and by what means he became acquainted with their language, and was initiated into their philosophy; as well as of many other particulars, which might have gratified the curiosity of his readers, and, perhaps, added credibility to his relation, he hath not thought fit to in- form us; these being matters proper for adepts only to know. SEC. tX.] THE PHILOSOPHY OF REID. 207 His account of their philosophy is as follows: ' ' The Idomenians, " saith he, " are many of them very ingenious, and much given to contemplation. In arith- metic, geometry, metaphysics, and physics, they have most elaborate systems. In the two latter, indeed, they have had many disputes carried on with great subtilty, and are divided into various sects; yet in the two former there hath been no less unanimity than among the hu- man species. Their principles relating to numbers and arithmetic, making allowance for their notation, differ in nothing from ours but their geometry differs very con- siderably. " As our author's account of the geometry of the Ido- menians agrees in everything with the geometry of visibles, of which we have already given a specimen, we shall pass over it. He goes on thus: "Colour, extension, and fig- ure, are conceived to be the essential properties of body. A very considerable sect maintains, that colour is the essence of body. If there had been no colour, say they, there had been no perception or sensation. Colour is all that we perceive, or can conceive, that is peculiar to body; extension and figure being modes common to body and to empty space. And if we should suppose a body to be annihilated, colour is the only thing in it that can be annihilated; for its place, and consequently the fig- ure and extension of that place, must remain, and can- not be imagined not to exist. These philosophers hold space to be the place of all bodies, immovable and in- destructible, without figure and similar in all its parts, incapable of increase or diminution, yet not unmeasura- ble; for every the least part of space bears a finite ratio to the whole. So that with them the whole extent of space is the common and natural measure of everything that hath length and breadth; and the magnitude of every body and of every figure is expressed by its being such a part of the universe. In like manner, the common and natural measure of length is an infinite right line, which, 208 THE PHILOSOPHY OF REID. [Cn. VI. as hath been before observed, returns into itself, and hath no limits, but bears a finite ratio to every other line. " As to their natural philosophy, it is now acknow- ledged by the wisest of them to have been for many ages in a very low state. The philosophers observing, that body can differ from another only in colour, figure, or magnitude, it was taken for granted, that all their particu- lar qualities must arise from the various combinations of these their essential attributes; and, therefore, it was looked upon as the end of natural philosophy, to shew how the various combinations of these three qualities in different bodies produced all the phenomena of nature. It were endless to enumerate the various systems that were invented with this view, and the disputes that were carried on for ages; the followers of every system ex- posing the weak sides of other systems, and palliating those of their own with great art. "At last, some free and facetious spirits, wearied with eternal disputation, and the labour of patching and propping weak systems, began to complain of the sub- tilty of nature; of the infinite changes that bodies under- go in figure, colour, and magnitude; and of the difficulty of accounting for these appearances making this a pre- tence for giving up all inquiries into the causes of things, as vain and fruitless. " These wits had ample matter of mirth and ridicule in the systems of philosophers; and, finding it an easier task to pull down than to build or support, and that every sect furnished them with arms and auxiliaries to destroy another, they began to spread mightily, and went on with great success. Thus philosophy gave way to scepticism and irony, and those systems which had been the work of ages, and the admiration of the learned, became the jest of the vulgar: for even the vulgar readily took part in the triumph over a kind of learning which they had long suspected, because it produced nothing but wrangling and altercation. The wits, having now SEC. IX.] THE PHILOSOPHY OF REID. 209 acquired great reputation, and being flushed with suc- cess, began to think their triumph incomplete, until every pretence to knowledge was overturned ; and ac- cordingly began their attacks upon arithmetic, geometry, and even upon the common notions of untaught Ido- menians. So difficult it hath always been," says our author, "for great conquerors to know where to stop. ' ' In the meantime, natural philosophy began to rise from its ashes, under the direction of a person of great genius, who is looked upon as having had something in him above Idomenian nature. He observed, that the Idomenian faculties were certainly intended for con- templation, and that the works of nature were a nobler subject to exercise them upon, than the follies of systems, or the errors of the learned ; and being sensible of the difficulty of rinding out the causes of natural things, he proposed, by accurate observation of the phenomena of nature, to find out the rules according to which they happen, without inquiring into the causes of those rules. In this he made considerable progress himself, and planned out much work for his followers, who call them- selves inductive philosophers. The sceptics look with envy upon this rising sect, as eclipsing their reputation, and threatening to limit their empire; but they are at a loss on what hand to attack it. The vulgar begin to reverence it as producing useful discoveries. "It is to be observed, that every Idomenian firmly believes, that two or more bodies may exist in the same place. For this they have the testimony of sense, and they can no more doubt of it, than they can doubt whether they have any perception at all. They often see two bodies meet and coincide in the same place, and separate again, without having undergone any change in their sensible qualities by this penetration. When two bodies meet, and occupy the same place, commonly one only appears in that place, and the other disappears. 210 THE PHILOSOPHY OF REID. [CH. VI. That which continues to appear is said to overcome, the other to be overcome. " To this quality of bodies they gave a name, which our author tells us hath no word answering to it in any hu- man language. And, therefore, after making a long apology, which I omit, he begs leave to call it the over- coming quality of bodies. He assures us, that " the spec- ulations which had been raised about this single quality of bodies, and the hypotheses contrived to account for it, were sufficient to fill many volumes. Nor have there been fewer hypotheses invented by their philosophers, to account for the changes of magnitude and figure; which, in most bodies that move, they perceive to be in a continual fluctuation. The founder of the inductive sect, believing it to be above the reach of Idomenian faculties, to discover the real causes of these phenomena, applied himself to find from observation, by what laws they are connected together ; and discovered many mathematical ratios and relations concerning the motions, magnitudes, figures, and overcoming quality of bodies, which con- stant experience confirms. But the opposers of this sect choose rather to content themselves with feigned causes of these phaenomena, than to acknowledge the real laws whereby they are governed, which humble their pride, by being confessedly unaccountable." Thus far Johannes Rudolphus Anepigraphus. Whe- ther this Anepigraphus be the same who is recorded among the Greek alchemistical writers not yet published, by Borrichius, Fabricius, and others, I do not pretend to determine. The identity of their name, and the simil- itude of their studies, although no slight arguments, yet are not absolutely conclusive. Nor will I take upon me to judge of the narrative of this learned traveller, by the external marks of his credibility ; I shall confine myself to those which the critics call internal It would even be of small importance to inquire, whether the Idome- mans have a real, or only an ideal existence; since this SEC. X.] THE PHILOSOPHY OF REID. 211 is disputed among the learned with regard to things with which we are more nearly connected. The important question is, whether the account above given, is a just account of their geometry and philosophy ? We have all the faculties which they have, with the addition of others which they have not; we may, therefore, form some judgment of their philosophy and geometry, by separat- ing from all others, the perceptions we have by sight and reasoning upon them. As far as I am able to judge in this way, after a careful examination, their geometry must be such as Anepigraphus hath described. Nor does his account of their philosophy appear to contain any evident marks of imposture; although here, no doubt, proper allowance is to be made for liberties which travellers take, as well as for involuntary mistakes which they are apt to fall into. Section X. OF THE PARALLEL MOTION OF THE EYES. Having explained, as distinctly as we can, visible fig- ure, and shewn its connection with the things signified by it, it will be proper next to consider some phaenom- ena of the eyes, and of vision, which have commonly been referred to custom, to anatomical or to mechanical causes ; but which, as I conceive, must be resolved into original powers and principles of the human mind ; and, therefore, belong properly to the subject of this inquiry. The first is the parallel motion of the eyes ; by which, when one eye is turned to the right or to the left, up- wards or downwards, or straight forwards, the other al- ways goes along with it in the same direction. We see plainly, when both eyes are open, that they are always turned the same way, as if both were acted upon by the ame motive force ; and if one eye is shut, and the hand 212 THE PHILOSOPHY OF REID. [Cn. VI. laid upon it, while the other turns various ways, we feel the eye that is shut turn at the same time, and that whether we will or not. What makes this phenomenon surprising is, that it is acknowledged, by all anatomists, that the muscles which move the two eyes, and the nerves which serve these muscles, are entirely distinct and unconnected. It would be thought very surprising and unaccountable to see a man, who, from his birth, never moved one arm, without moving the other precisely in the same manner, so as to keep them always parallel yet it* would not be more difficult to find the physical cause of such motion of the arms, than it is to find the cause of the parallel motion of the eyes, which is perfectly simi- lar. The only cause that hath been assigned of this parallel motion of the eyes, is custom. We find by experience, it is said, when we begin to look at objects, that, in order to have distinct vision, it is necessary to turn both eyes the same way ; therefore, we soon acquire the habit of doing it constantly, and by degrees lose the power of doing otherwise. This account of the matter seems to be insufficient ; because habits are not got at once ; it takes time to ac- quire and to confirm them ; and if this motion of the eyes were got by habit, we should see children, when they are born, turn their eyes different ways, and move one without the other, as they do their hands or legs. I know some have affirmed that they are apt to do so. But I have never found it true from my own observation, although I have taken pains to make observations of this kind, and have had good opportunities. I have likewise consulted experienced midwives, mothers, and nurses, and found them agree, that they had never ob- served distortions of this kind in the eyes of children, but when they had reason to suspect convulsions, or some preternatural cause. It seems, therefore, to be extremely probable, that, SEC. X.] THE PHILOSOPHY OF REID. 213 previous to custom, there is something in the constitu- tion, some natural instinct, which directs us to move both eyes always the same way. We know not how the mind acts upon the body, nor by what power the muscles are contracted and relaxed but we see that, in some of the voluntary, as well as in some of the involuntary motions, this power is so di- rected, that many muscles which have no material tie or connection, act in concert, each of them being taught to play its part in exact time and measure. Nor doth a company of expert players in a theatrical performance, or of excellent musicians in a concert, or of good dancers in a country dance, with more regularity and order, conspire and contribute their several parts, to produce one uniform effect, than a number of muscles do, in many of the animal functions, and in many voluntary actions. Yet we see such actions no less skilfully and regularly performed in children, and in those who know not that they have such muscles, than in the most skilful anatomist and physiologist. Who taught all the muscles that are concerned in sucking, in swallowing our food, in breathing, and in the several natural expulsions, to act their part in such regular order and exact measure ? It was not custom surely. It was that same powerful and wise Being who made the fabric of the human body, and fixed the laws by which the mind operates upon every part of it, so that they may answer the purposes intended by them. And when we see, in so many other instances, a system of unconnected muscles conspiring so wonderfully in their several functions, without the aid of habit, it needs not be thought strange, that the muscles of the eyes should, without this aid, conspire to give that direction to the eyes, without which they could not answer their end. We see :. like conspiring action in the muscles which contract the pupils of the two eyes ; and in those mus- 214 THE PHILOSOPHY OF REID. [CH. VI. cles, whatever they be, by which the conformation of the eyes is varied according to the distance of objects. It ought, however, to be observed, that, although it appears to be by natural instinct that both eyes are al- ways turned the same way, there is still some latitude left for custom. What we have said of the parallel motion of the eyes, is not to be understood so strictly as if nature directed us to keep their axes always precisely and mathemati- cally parallel to each other. Indeed, although they are always nearly parallel, they hardly ever are exactly so. When we look at an object, the axes of the eyes meet in that object : and, therefore, make an angle, which is always small, but will be greater or less, according as the object is nearer or more remote. Nature hath very wisely left us the power of varying the parallelism of our eyes a little, so that we can direct them to the same point, whether remote or near. This, no doubt, is learned by custom : and accordingly we see, that it is a long time before children get this habit in perfection. This power of varying the parallelism of the eyes is naturally no more than is sufficient for the purpose in- tended by it ; but by much practice and straining, it may be increased. Accordingly, we see, that some have ac- quired the power of distorting their eyes into unnatural directions, as others have acquired the power of distort- ing their bodies into unnatural postures. Those who have lost the sight of an eye, commonly lose what they had got by custom, in the direction of their eyes, but retain what they had by nature ; that is, although their eyes turn and move always together, yet, when they look upon an object, the blind eye will often have a very small deviation from it ; which is not per- ceived by a slight observer, but may be discerned by one accustomed to make exact observations in these matters. SEC. XI.] THE PHILOSOPHY OF REID. 215 Section XL OF OUR SEEING OBJECTS ERECT BY INVERTED IMAGES. Another phenomenon which hath perplexed philoso- phers, is our seeing objects erect, when it is well known that their images or pictures upon the tunica retina of the eye are inverted. The sagacious Kepler first made the noble discovery, that distinct but inverted pictures of visible objects are formed upon the retina by the rays of light coming from the object. The same great philosopher demon- strated, from the principles of optics, how these pictures are formed to wit, That the rays coming from any one point of the object, and falling upon the various parts of the pupil, are, by the cornea and crystalline, refracted so as to meet again in one point of the retina, and there paint the colour of that point of the object from which they come. As the rays from different points of the ob- ject cross each other before they come to the retina, the picture they form must be inverted; the upper part of the object being painted upon the lower part of the retina, the right side of the object upon the left of the retina, and so of the other parts. This philosopher thought chat we see objects erect by means of these inverted pictures, for this reason, that, as the rays from different points of the object cross each other before they fall upon the retina, we conclude that the impulse which we feel upon the lower part of the retina comes from above, and that the impulse which we feel upon the higher part comes from below. Des Cartes afterwards gave the same solution of this phenomenon, and illustrated it by the judgment which we form of the position of objects which we feel with our arms crossed, or with two sticks that cross each other. But we cannot acquiesce in this solution. First, Be- 2l6 THE PHILOSOPHY OF REID. [Cn. VI. cause it supposes our seeing things erect, to be a deduc- tion of reason, drawn from certain premises: whereas it seems to be an immediate perception. And, secondly, Because the premises from which all mankind are sup- posed to draw this conclusion, never entered into the minds of the far greater part, but are absolutely un- known to them. We have no feeling or perception of the pictures upon the retina, and as little surely of the position of them. In order to see objects erect, accord- ing to the principles of Kepler or Des Cartes, we must previously know that the rays of light come from the ob- ject to the eye in straight lines; we must know that the rays from different points of the object cross one another before they form the pictures upon the retina; and, lastly, we must know that these pictures are really inverted. Now, although all these things are true, and known to philosophers, yet they are absolutely unknown to the far greatest part of mankind: nor is it possible that they who are absolutely ignorant of them, should reason from them, and build conclusions upon them. Since, there- fore, visible objects appear erect to the ignorant as well as to the learned, this cannot be a conclusion drawn from premises which never entered into the minds of the ig- norant. We have indeed had occasion to observe many instances of conclusions drawn, either by means of original principles, or by habit, from premises which pass through the mind very quickly, and which are never made the objects of reflection; but surely no man will conceive it possible to draw conclusions from prem- ises which never entered into the mind at all. Bishop Berkeley having justly rejected 'this solution, gives one founded upon his own principles; wherein he is followed by the judicious Dr. Smith, in his "Optics; " and this we shall next explain and examine. That ingenious writer conceives the ideas of sight to be altogether unlike those of touch. And, since the notions we have of an object by these different senses SEC. XI.] THE PHILOSOPHY OF REID. 2I/ have no similitude, we can learn only by experience how one sense will be affected, by what, in a certain manner, affects the other. Figure, position, and even number, in tangible objects, are ideas of touch; and, although there is no similitude between these and the ideas of sight, yet we learn by experience, that a triangle affects the sight in such a manner, and that a square affects it in such another manner hence we judge that which af- fects it in the first manner, to be a triangle, and that which affects it in the second, to be a square. In the same way, finding, from experience, that an object in an erect position affects the eye in one manner, and the same object in an inverted position affects it in another, we learn to judge, by the manner in which the eye is affected, whether the object is erect or inverted. In a word, visible ideas, according to this author, are signs of the tangible; and the mind passeth from the sign to the thing signified, not by means of any similitude between the one and the other, nor by any natural principle, but by having found them constantly conjoined in experi- ence,- as the sounds of a language are with the things they signify: so that, if the images upon the retina had been always erect, they would have shewn the objects erect, in the manner as they do now that they are in- verted nay, if the visible idea which we now have from an inverted object, had been associated from the begin- ning with the erect position of that object, it would have signified an erect position, as readily as it now sig- nifies an inverted one. And, if the visible appearance of two shillings had been found connected from the be- ginning with the tangible idea of one shilling, that appearance would as naturally and readily have sig- nified the unity of the object as now it signifies its duplicity. This opinion is, undoubtedly, very ingenious : and, if it is just, serves to resolve not only the phaenomenon now under consideration, but likewise that which we 2l8 THE PHILOSOPHY OF REID, |CH. VI. shall next consider our seeing objects single with two eyes. It is evident that, in this solution, it is supposed that we do not originally, and previous to acquired habits, see things either erect or inverted, of one figure or another, single or double ; but learn, from experience, to judge of their tangible position, figure, and number, by certain visible signs. Indeed, it must be acknowledged to be extremely diffi- cult to distinguish the immediate and natural objects of sight, from the conclusions which we have been accus- tomed from infancy to draw from them. Bishop Berkeley was the first that attempted to distinguish the one from the other, and to trace out the boundary that divides them. And if, in doing so, he hath gone a little to the right hand or to the left, this might be expected in a sub- ject altogether new, and of the greatest subtilty. The nature of vision hath received great light from this dis- tinction ; and many phaenomena in optics, which before appeared altogether unaccountable, have been clearly and distinctly resolved by it. It is natural, and almost- un- avoidable, to one who hath made an important discovery in philosophy, to carry it a little beyond its sphere, and to apply it to the resolution of phaenomena which do not fall within its province. Even the great Newton, when he had discovered the universal law of gravitation, and observed how many of the phaenomena of nature depend upon this, and other laws of attraction and re- pulsion, could not help expressing his conjecture, that all the phaenomena of the material world depend upon attracting and repelling forces in the particles of matter. And I suspect that the ingenious Bishop of Cloyne, having found so many phaenomena of vision reducible to the con- stant association of the ideas of sight and touch, carried this principle a little beyond its just limits. In order to judge as well as we can whether it is so, let r.s suppose such a blind man as Dr. Saunderson, SEC. XL] THE PHILOSOPHY OF REID. 19 having all the knowledge and abilities which a blind man may have, suddenly made to see perfectly. Let us suppose him kept from all opportunities of associating his ideas of sight with those of touch, until the former become a little familiar; and the first surprise, occa- sioned by objects so new, being abated, he has time to canvass them, and to compare them, in his mind, with the notions which he formerly had by touch; and, in particular, to compare, in his mind, that visible exten- sion which his eyes present, with the extension in length and breadth with which he was before acquainted. We have endeavoured to prove, that a blind man may form a notion of the visible extension and figure of bod- ies, from the relation which it bears to their tangible extension and figure. Much more, when this visible extension and figure are presented to his eye, will he be able to compare them with tangible extension and figure, and to perceive that the one has length and breadth as well as the other; that the one may be bounded by lines, either straight or curve, as well as the other. And, therefore, he will perceive that there may be visible as well as tangible circles, triangles, quadrilateral and mul- tilateral figures. And, although the visible figure is jcoloured, and the tangible is not, they may, notwith- standing, have the same figure; as two objects of touch may have the same figure, although one is hot and the other cold. We have demonstrated, that the properties of visible figure differ from those of the plain figures which they represent; but it was observed, at the same time, that when the object is so small as to be seen distinctly at one view, and is placed directly before the eye, the dif- ference between the visible and the tangible figure is too small to be perceived by the senses Thus, it is true, that, of every visible triangle, the three angles are greater than two right angles; whereas, in a plain triangle, the three angles are equal to two right angles; but when the 220 THE PHILOSOPHY OF REID. [C H . VI. visible triangle is small, its three angles will be so nearly equal to two right angles, that the sense cannot discern the difference. In like manner, the circumferences of unequal visible circles are not, but those of plain circles are, in the ratio of their diameters; yet, in small visible circles, the circumferences are very nearly in the ratio of their diameters; and the diameter bears the same ratio to the circumference as in a plain circle, very nearly. Hence it appears, that small visible figures (and such only can be seen distinctly at one view) have not only a resemblance to the plain tangible figures which have the same name, but are to all senses the same: so that if Dr. Saunderson had been made to see, and had atten- tively viewed the figures of the first book of Euclid, he might, by thought and consideration, without touching them, have found out that they were the very figures he was before so well acquainted with by touch. When plain figures are seen obliquely, their visible figure differs more from the tangible ; and the representa- tion which is made to the eye, of solid figures, is still more imperfect ; because visible extension hath not three, but two dimensions only. Yet, as it cannot be said that an exact picture of a man hath no resemblance of the man, or that a perspective view of a house hath no resem- blance of the house, so it cannot be said, with any pro- priety, that the visible figure of a man or of a house'hath no resemblance of the objects which they represent. Bishop Berkeley therefore proceeds upon a capital mis- take, in supposing that there is no resemblance betwixt the extension, figure, and position which we see, and that which we perceive by touch. We may further observe, that Bishop Berkeley's sys- tem, with regard to material things, must have made him see this question, of the erect appearance of objects, in a very different light from that in which it appears to those who do not adopt his system. In his theory of vision, he seems indeed to allow, that SEC. XI.] THE PHILOSOPHY OF REID. 221 there is an external material world: but he believed that this external world is tangible only, and not visible ; and that the visible world, the proper object of sight, is not ex- ternal, but in the mind. If this is supposed, he that affirms that he sees things erect and not inverted, affirms that there is a top and a bottom, a right and a left in the mind. Now, I confess I am not so well acquainted with the topography of the mind, as to be able to affix a meaning to these words when applied to it. We shall therefore allow, that, if visible objects were not external, but existed only in the mind, they could have no figure, or position, or extension ; and that it would be absurd to affirm, that they are seen either erect or inverted, or that there is any resemblance between them and the objects of touch. But when we propose the question, why objects are seen erect and not inverted, we take it for granted, that we are not in Bishop Berke- ley's ideal world, but in that world which men who yield to the dictates of common sense, believe themselves to inhabit. We take it for granted, that the objects both of sight and touch, are external, and have a certain figure, and a certain position with regard to one another, and with regard to our bodies, whether we perceive it or not. When I hold my walking-cane upright in my hand, and look at it, I take it for granted that I see and handle the same individual object. When I say that I feel it erect, my meaning is, that I feel the head directed from the horizon, and the point directed towards it ; and when I say that I see it erect, I mean that I see it with the head directed from the horizon, and the point towards it. I conceive the horizon as a fixed object both of sight and touch, with relation to which, objects are said to be high or low, erect or inverted; and when the question is asked, why I see the object erect, and not inverted, it is the same as if you should ask, why I see it in that posi- tion which it really hath, or why the eye shews the real position of objects, and doth not shew them in an in- 222 HE PHILOSOPHY OF RElD. tCH. Vl. verted position, as they are seen by a common astronom- ical telescope, or as their pictures are seen upon the retina of an eye when it is dissected. Section XII. THE SAME SUBJECT CONTINUED. It is impossible to give a satisfactory answer to this question, otherwise than by pointing out the laws of nature which take place in vision ; for by these the phae- nomena of vision must be regulated. Therefore, I answer, First, That, by a law of nature, the rays of light proceed from every point of the object to the pupil of the eye, in straight lines ; Secondly, That, by the laws of nature, the rays coming from any one point of the object to the various parts of the pupil, are so refracted as to meet again in one point of the retina ; and the rays from different points of the object, first crossing each other, and then proceeding to as many different points of the retina, form an inverted picture of the object. So far the principles of optics carry us ; and experience further assures us, that, if there is no such picture upon the retina, there is no vision ; and that such as the picture on the retina is, such is the appearance of the object, in colour and figure, distinctness or indistinctness, bright- ness or faintness. It is evident, therefore, that the pictures upon the ret- ina are, by the laws of nature, a mean of vision; but in what way they accomplish their end, we are totally ignorant. Philosophers conceive, that the impression made on the retina by the rays of light, is communicated to the optic nerve, and by the optic nerve conveyed to some part of the brain, by them called the sensorium; and that the impression thus conveyed to the sensorium SEC. XII.] THE PHILOSOPHY OF REID. 12$ is immediately perceived by the mind, which is supposed to reside there. But we know nothing of the seat of the soul: and we are so far from perceiving immediately what is transacted in the brain, that of all parts of the human body we know least about it. It is indeed very probable, that the optic nerve is an instrument of vision no less necessary than the retina; and that some impres- sion is made upon it, by means of the pictures on the retina. But of what kind this impression is, we know nothing. There is not the least probability that there is any picture or image of the object either in the optic nerve or brain. The pictures on the retina are formed by the rays of light; and, whether we suppose, with some, that their impulse upon the retina causes some vibration of the fibres of the optic nerve, or, with others, that it gives motion to some subtile fluid contained in the nerve, neither that vibration nor this motion can resemble the visible object which is presented to the mind. Nor is there any probability that the mind perceives the pictures upon the retina. These pictures are no more objects of our perception, than the brain is, or the optic nerve. No man ever saw the pictures in his own eye, nor in- deed the pictures in the eye of another, until it was taken out of the head and duly prepared. It is very strange, that philosophers, of all ages, should ] have agreed in this notion, that the images of external objects are conveyed by the organs of sense to the brain, and are there perceived by the mind. Nothing can be more unphilosophical. For, First, This notion hath no foundation in fact and observation. Of all the organs of sense, the eye only, as far as we can discover, forms any kind of image of its object; and the images formed by the eye are not in the brain, but only in the bottom of the eye; nor are they at all perceived or felt by the mind. Secondly, It is as difficult to conceive how the mind perceives images in the brain, as how it perceives things 24 THE PHILOSOPHY OF REID. [CH. VI. more distant. If any man will shew how the mind may perceive images in the brain, I will undertake to shew how it may perceive the most distant objects; for, if we give eyes to the mind, to perceive what is transacted at home in its dark chamber, why may we not make these eyes a little longer-sighted ? and then we shall have no occasion for that unphilosophical fiction of images in the brain. In a word, the manner and mechanism of the mind's perception is quite beyond our comprehension; and this way of explaining it, by images in the brain, seems to be founded upon very gross notions of the mind and its operations; as if the supposed images in the brain, by a kind of contact, formed similar impres- sions or images of objects upon the mind, of which im- pressions it is supposed to be conscious, We have endeavoured to shew, throughout the course of this inquiry, that the impressions made upon the mind by means of the five senses, have not the least resem- blance to the objects of sense; and, therefore, as we see no shadow of evidence that there are any such images in the brain, so we see no purpose, in philosophy, that the supposition of them can answer. Since the picture upon the retina, therefore, is neither itself seen by the mind, nor produces any impression upon the brain or sensorium, which is seen by the mind, nor makes any impression upon the mind that resembles the object, it may still be asked, How this picture upon the retina causes vision ? Before we answer this question, it is proper to observe, that, in the operations of the mind, as well as in those of bodies, we must often be satisfied with knowing that cer- tain things are connected, and invariably follow one another, without being able to discover the chain that goes between them. It is to such connections that we give the name of laws of nature-, and when we say that one thing produces another by a law of nature, this sig- nifies no more, but that one thing, which we call in popular language the cause, is constantly and invariably SEC. XII.] THE PHILOSOPHY OF REID. 225 followed by another, which we call the effect; and that we know not how they are connected. Thus, we see it is a fact, that bodies gravitate towards bodies; and that this gravitation is regulated by certain mathematical pro- portions, according to the distances of the bodies from each other, and their quantities of matter. Being un- able to discover the cause of this gravitation, and pre- suming that it is the immediate operation, either of the Author of nature, or of some subordinate cause, which we have not hitherto been able to reach, we call it a law of nature. If any philosopher should hereafter be so happy, as to discover the cause of gravitation, this can only be done by discovering some more general law of nature, of which the gravitation of bodies is a necessary consequence. In every chain of natural causes, the highest link is a primary law of nature, and the highest link which we can trace, by just induction, is either this primary law of nature, or a necessary consequence of it. To trace out the laws of nature, by induction from the phenomena of nature, is all that true philosophy aims at, and all that it can ever reach. There are laws of nature by which the operations of the mind are regulated, there are also laws of nature that govern the material system ; and, as the latter are the ulti- mate conclusions which the human faculties can reach in the philosophy of bodies, so the former are the ultimate conclusions we can reach in the philosophy of minds. To return, therefore, to the question above proposed, we may see, from what hath been just now observed, that it amounts to this By what law of nature is a picture upon the retina the mean or occasion of my seeing an ex- ternal object of the same figure and colour in a contrary position, and in a certain direction from the eye ? It will, without doubt, be allowed that I see the whole object in the same manner and by the same law by which I see any one point of it. Now I know it to be a fact, that, in direct vision, I see every point of the object in the 226 THE PHILOSOPHY OF REID. [Cn. VI. direction of the right line that passeth from the centre of the eye to that point of the object. And I know, like- wise, from optics, that the ray of light that comes to the centre of my eye, passes on to the retina in the same direction. Hence, it appears to be a fact, that every point of the object is seen in the direction of a right line passing from the picture of that point, on the retina, through the centre of the eye. As this is a fact that holds universally and invariably, it must either be a law of nature or the necessary consequence of some more general law of nature; and, according to the just rules of philosophising, we may hold it for a law of nature, until some more general law be discovered, whereof it is a necessary con- sequence which, I suspect, can never be done. Thus, we see that the phaenomena of vision lead us by the hand to a law of nature, or a law of our constitution, of which law, our seeing objects erect by inverted images, is a necessary consequence. For it necessarily follows, from the law we have mentioned, that the object whose picture is lowest on the retina must be seen in the highest direction from the eye; and that the object whose picture is on the right of the retina must be seen on the left; so that, if the pictures had been erect in the retina, we should have seen the object inverted. My chief intention in handling this question, was to point out this law of nature, which, as it is a part of the constitution of the human mind, belongs properly to the subject of this inquiry. For this reason, I shall make some farther remarks upon it, after doing justice to the ingenious Dr. Porterfield, who long ago, in the " Medical Essays," or, more lately, in his "Treatise of the Eye," pointed out, as a primary law of our nature, That a visible object ap- pears in the direction of a right line perpendicular to the retina at that point where its image is painted. If lines drawn from the centre of the eye to all parts of the retina be perpendicular to it, as they must be very nearly, this coincides with the law we have mentioned, and is the SEC. XII.] THE PHILOSOPHY OF REID. 227 same in other words. In order, therefore, that we may have a more distinct notion of this law of our constitution, we may observe 1. That we can give no reason why the retina is, of all parts of the body, the only one on which pictures made by the rays of light cause vision; and, therefore, we must resolve this solely into a law of our constitution. We may form such pictures by means of optical glasses, upon the hand, or upon *any other part of the body; but they are not felt, nor do they produce anything like vision. A picture upon the retina is as little felt as one upon the hand; but it produces vision, for no other reason that we know, but because it is destined by the wisdom of nature to this purpose. The vibrations of the air strike upon the eye, the palate, and the olfactory membrane, with the same force as upon the membrani tympani of the ear. The impression they make upon the last produces the sensation of sound; but their impres- sion upon any of the former produces no sensation at all. This may be extended to all the senses, whereof each hath its peculiar laws, according to which the impres- sions made upon the organ of that sense, produce sensa- tions or perceptions in the mind, that cannot be pro- duced by impressions made upon any other organ. 2. We may observe, that the laws of perception, by the different senses, are very different, not only in re- spect of the nature of the objects perceived by them, but likewise in respect of the notices they give us of the dis- tance and situation of the object. In all of them the object is conceived * to be external, and to have real existence, independent of our perception : but in one, the distance, figure, and situation of the object, are all * The common sense of mankind assures us that the object of sense, is not merely conceived to be external, but perceived in its ex- ternality; that we know the Non-Ego, not merely mediately, by a representation in the Ego, but immediately, as existing though only as existing in relation to our organs. H. 228 THE PHILOSOPHY OF REID. [CH. VI. presented to the mind; in another, the figure and situa- tion, but not the distance; and in others, neither figure, situation, nor distance. In vain do we attempt to ac- count for these varieties in the manner of perception by the different senses, from principles of anatomy or natural philosophy. They must at last be resolved into the will of our Maker, who intended that our powers of percep- tion should have certain limits, and adapted the organs of perception, and the laws of nature by which they operate, to his wise purposes. When we hear an unusual sound, the sensation indeed is in the mind, but we know that there is something ex- ternal that produced this sound. At the same time, our hearing does not inform us whether the sounding body is near or at a distance, in this direction or that ; and therefore we look round to discover it. If any new phaenomenon appears in the heavens, we see exactly its colour, its apparent place, magnitude, and figure; but we see not its distance. It may be in the at- mosphere, it may be among the planets, or it may be in the sphere of the fixed stars, for anything the eye can de- termine. The testimony of the sense of touch reaches only to objects that are contiguous to the organ, but, with re- gard to them, is more precise and determinate. When we feel a body with our hand, we know the figure, dis- tance, and position of it, as well as whether it is rough or smooth, hard or soft, hot or cold. The sensations of touch, of seeing, and hearing, are all in the mind, and can have no existence but when they are perceived. How do they all constantly and in- variably suggest the conception and belief of external objects, which exist whether they are perceived or not ? No philosopher can give any other answer to this, but that such is the constitution of our nature. How do we know that the object of touch is at the finger's end, and nowhere else ? that the object of sight is in such a di- SEC. XII.] THE PHILOSOPHY OF REID. 229 rection from the eye, and in no other, but maybe at any distance ? and that the object of hearing may be at any distance, and in any direction ? Not by custom surely not by reasoning, or comparing ideas but by the constitution of our nature. How do we perceive visible objects in the direction of right lines perpendicular to that part of the retina on which the rays strike, while we do not perceive the objects of hearing in lines perpendic- ular to the membrana tympani upon which the vibrations of the air strike ? Because such are the laws of our na- ture. How do we know the parts of our bodies affected by particular pains ? Not by experience or by reason- ing, but by the constitution of nature. The sensation of pain is, no doubt, in the mind, and cannot be said to have any relation, from its own nature, to any part of the body; but this sensation, by our constitution, gives a perception of some particular part of the body, whose disorder causes the uneasy sensation. If it were not so, a man who never before felt either the gout or the tooth- ache, when he is first seized with the gout in his toe, might mistake it for the toothache. Every sense, therefore, hath its peculiar laws and limits, by the constitution of our nature; and one of the laws of sight is, that we always see an object in the di- rection of a right line, passing from its image on the ret- ina through the centre of the eye. 3. Perhaps some readers will imagine that it is easier, and will answer the purpose as well, to conceive a law of nature, by which we shall always see objects in the place in which they are, and in their true position, with- out having recourse to images on the retina, or to the optical centre of the eye. To this I answer, that nothing can be a law of nature which is contrary to fact. The law.s of nature are the most general facts we can discover in the operations of nature. Like other facts, they are not to be hit upon by a happy conjecture, but justly deduced from observation; 230 THE PHILOSOPHY OF REID. [Cn. VI. like other general facts, they are not to be drawn from a few particulars, but from a copious, patient, and cautious induction. That we see things always in their true place and position, is not fact; and therefore it can be no law of nature. In a plain mirror, I see myself, and other things, in places very different from those they really occupy. And so it happens in every instance wherein the rays coming from the object are either re- flected or refracted before falling upon the eye. Those who know anything of optics, know that, in all such cases, the object is seen in the direction of a line passing from the centre of the eye, to the point where the rays were last reflected or refracted; and that upon this all the powers of the telescope and microscope depend. Shall we say, then, that it is a law of nature, that the object is seen in the direction which the rays have when they fall on the eye, or rather in the direction contrary to that of the rays when they fall upon the eye ? No. This is not true; and therefore it is no law of nature. For the rays, from any one point of the object, come to all parts of the pupil; and therefore must have different directions: but we see the object only in one of these di- rections to wit, in the direction of the rays that come to the centre of the eye. And this holds true, even when the rays that should pass through the centre are stopped, and the object is seen by rays that pass at a dis- tance from the centre. Perhaps it may still be imagined, that, although we are not made so as to see objects always in their true place, nor so as to see them precisely in the direction of the rays when they fall upon the cornea; yet we may be so made as to see the object in the direction which the rays have when they fall upon the retina, after they have undergone all their refractions in the eye that is, in the direction in which the rays pass from the crystalline to the retina. But neither is this true ; and consequently it is no law of our constitution. In order to see that it is SEC. XII.] THE PHILOSOPHY OF REID. 231 not true, we must conceive all the rays that pass from the crystalline to one point of the retina, as forming a small cone, whose base is upon the back of the crystal- line, and whose vertex is a point of the retina. It is evi- dent that the rays which form the picture in this point, have various directions, even after they pass the crystal- line: yet the object is seen only in one of these directions to wit, in the direction of the rays that come from the centre of the eye. Nor is this owing to any particular virtue in the central rays, or in the centre itself; for the central rays may be stopped. When they are stopped, the image will be formed upon the same point of the retina as before, by rays that are not central, nor have the same direction which the central rays had: and in this case the object is seen in the same direction as be- fore, although there are now no rays corning in that di- rection. From this induction we conclude, That our seeing an object in that particular direction in which we do see it, is not owing to any law of nature by which we are made to see it in the direction of the rays, either before their refractions in the eye, or after, but to a law of our na- ture, by which we see the object in the direction of the right line that passeth from the picture of the object upon the retina to the centre of the eye. The facts upon which I ground this induction, are taken from some curious experiments of Scheiner, in his "Fundamentum Opticum," quoted by Dr. Porterfield, and confirmed by his experience. I have also repeated these experiments, and found them to answer. As they are easily made, and tend to illustrate and confirm the law of nature I have mentioned, I shall recite them as briefly and distinctly as I can. Experiment i. Let a very small object, such as the head of a pin, well illuminated, be fixed at such a dis- tance from the eye as to be beyond the nearest limit and within the farthest limit of distinct vision. For a young 232 THE PHILOSOPHY OF REID. [Cn. VI. eye, not near-sighted, the object may be placed at the distance of eighteen inches. Let the eye be kept steadily in one place, and take a distinct view of the object. We know, from the principles of optics, that the rays from any one point of this object, whether they pass through the centre of the eye, or at any distance from the centre which the breadth of the pupil will permit, do all unite again in one point of the retina. We know, also, that these rays have different directions, both be- fore they fall upon the eye, and after they pass through the crystalline. Now, we can see the object by any one small parcel of these rays, excluding the rest, by looking through a small pin-hole in a card. Moving this pin-hole over the various parts of the pupil, we can see the object, first by the rays that pass above the centre of the eye, then by the central rays, then by the rays that pass below the centre, and in like manner by the rays that pass on the right and left of the centre. Thus, we view this object, successively, by rays that are central, and by rays that are not central ; by rays that have different di- rections, and are variously inclined to each other, both when they fall upon the cornea, and when they fall upon the retina; but always by rays which fall upon the same point of the retina. And what is the event ? It is this that the object is seen in the same individual direction, whether seen by all these rays together, or by any one parcel of them. Experiment 2. Let the object above mentioned be now placed within the nearest limit of distinct vision that is, for an eye that is not near-sighted, at the dis- tance of four or five inches. We know that, in this case, the rays coming from one point of the object do not meet in one point of the retina, but spread over a small circular spot of it; the central rays occupying the centre of this circle, the rays that pass above the centre occupy- ing the upper part of the circular spot, and so of the rest. SEC. Xit.) THE PHILOSOPHY OF REID. 233 And we know that the object is, in this case, seen con- fused; every point of it being seen, not in one, but in va- rious directions. To remedy this confusion, we look at the object through the pin-hole, and while we move the pin-hole over the various parts of the pupil, the object does not keep its place, but seems to move in a contrary direction. It is here to be observed, that, when the pin-hole is carried upwards over the pupil, the picture of the object is carried upwards upon the retina, and the object, at the same time, seems to move downwards, so as to be always in the right line, passing from the picture through the centre of the eye. It is likewise to be observed, that the rays which form the upper and the lower pictures upon the retina do not cross each other, as in ordinary vision ; yet, still, the higher picture shews the object lower, and the lower picture shews the object higher, in the same manner as when the rays cross each other. Whence we may observe, by the way, that this phaenom- enon of our seeing objects in a position contrary to that of their pictures upon the retina, does not depend upon the crossing of the rays, as Kepler and Des Cartes con- ceived. Experiment 3. Other things 'remaining as in the last experiment, make three pin-holes in a straight line, so near that the rays coming from the object through all the holes may enter the pupil at the same time. In this case, we have a very curious phaenomenon ; for the ob- ject is seen triple with one eye. And if you make more holes within the breadth of the pupil, you will see as many objects as there are holes. However, we shall sup- pose them only three one on the right, one in the mid- dle and one on the left ; in which case you see three ob- jects standing in a line from right to left. It is here to be observed, that there are three pictures on the retina ; that on the left being formed by the rays which pass on the left of the eye's centre, the middle 234 THE PHILOSOPHY OF REID, tCn. VI. picture being formed by the central rays, and the right- hand picture by the rays which pass on the right of the eye's centre. It is farther to be observed, that the ob- ject which appears on the right, is not that which is seen through the hole on the right, but that which is seen through the hole on the left ; and, in like manner, the left-hand object is seen through the hole on the right, as is easily proved by covering the holes successively : so that, whatever is the direction of the rays which form the right-hand and left-hand pictures, still the right-hand picture shews a left-hand object, and the left-hand pict- ure shews a right-hand object. Experiment 4. It is easy to see how the two last ex- periments may be varied, by placing the object beyond the farthest limit of distinct vision. In order to make this experiment, I looked at a candle at the distance of ten feet, and put the eye of my spectacles behind the card, that the rays from the same point of the object might meet and cross each other, before they reached the retina. In this case, as in the former, the candle was seen triple through the three pin-holes ; but the candle on the right was seen through the hole on the right ; and, on the contrary, the left-hand candle was seen through the hole on the left. In this experiment it is evident, from the principles of optics, that the rays fcfrming the several pictures on the retina cross each other a little before they reach the retina ; and, therefore, the left-hand picture is formed by the rays which pass through the hole on the right : so that the position of the pictures is contrary to that of the holes by which they are formed ; and, therefore, is also contrary to that of their objects as we have found it to be in the former experiments. These experiments exhibit several uncommon phae- nomena, that regard the apparent place, and the direc- tion of visible objects from the eye ; phenomena that seem to be most contrary to the common rules of vision. SEC. XII.) THE PHILOSOPHY OF REID. 235 When we look at the same time through three holes that are in a right line, and at certain distances from each other, we expect that the objects seen through them should really be, and should appear to be, at a distance from each other. Yet, by the first experiment, we may, through three such holes, see the same object, and the same point of that object ; and through all the three it appears in the same individual place and direction. When the rays of light come from the object in right lines to the eye, without any reflection, inflection, or refraction, we expect that the object should appear in its real and proper direction from the eye ; and so it commonly does. But in the second, third, and fourth experiments, we see the object in a direction which is not its true and real direction from the eye, although the rays come from the object to the eye, without any in- flection, reflection, or refraction. When both the object and the eye are fixed without the least motion, and the medium unchanged, we expect that the object should appear to rest, and keep the same place. Yet, in the second and fourth experiments, when both the eye and the object are at rest, and the medium unchanged, we make the object appear to move upwards or downwards, or in any direction we please. When we look, at the same time and with the same eye, through holes that stand in a line from right to left, we expect that the object seen through the left-hand hole should appear on the left, and the object seen through the right-hand hole should appear on the right. Yet, in the third experiment, we find the direct contrary. Although many instances occur in seeing the same ob- ject double with two eyes, we always expect that it should appear single when seen only by one eye. Yet, in the second and fourth experiments, we have instances wherein the same object may appear double, triple, or quadruple to one eye, without the help of a polyhedron or multiplying glass. 236 THE PHILOSOPHY OF REID. [CH. VI. All these extraordinary phenomena, regarding the di- rection of visible objects from the eye, as well as those that are common and ordinary, lead us to that law of nature which I have mentioned, and are the necessary consequences of it. And, as there is no probability that we shall ever be able to give a reason why pictures upon the retina make us see external objects, any more than pictures upon the hand or upon the cheek ; or, that we shall ever be able to give a reason, why we see the ob- ject in the direction of a line passing from its picture through the centre of the eye, rather than in any other direction I am, therefore, apt to look upon this law as a primary law of our constitution. To prevent being misunderstood, I beg the reader to observe, that I do not mean to affirm that the picture upon the retina will make us see an object in the direc- tion mentioned, or in any direction, unless the optic nerve, and the other more immediate instruments of vis- ion, be sound, and perform their function. We know not well what is the office of the optic nerve, nor in what manner it performs that office ; but that it hath some part in the faculty of seeing, seems to be certain ; be- cause, in an amaurosis, which is believed to be a dis- order of the optic nerve, the pictures on the retina are clear and distinct, and yet there is no vision. We know still less of the use and function of the choroid membrane ; but it seems likewise to be neces- sary to vision : for it is well known, that pictures upon that part of the retina where it is not covered by the choroid I mean at the entrance of the optic nerve produce no vision any more than a picture upon the hand. We acknowledge, therefore, that the retina is not the last and most immediate instrument of the mind in vision. There are other material organs, whose oper- ation is necessary to seeing, even after the pictures upon the retina are formed. If ever we come to know the structure and use of the choroid membrane, the optic SfiC. XII.] THE PHILOSOPHV OF REID. $37 nerve, and the brain, and what impressions are made upon them by means of the pictures on the retina, some more links of the chain may be brought within our view, and a more general law of vision discovered ; but, while we know so little of the nature and office of these more immediate instruments of vision, it seems to be im- possible to trace its laws beyond the pictures upon the retina. Neither do I pretend to say, that there may not be diseases of the eye, or accidents, which may occasion our seeing objects in a direction somewhat different from that mentioned above. I shall beg leave to mention one instance of this kind that concerns myself. In May, 1761, being occupied in making an exact meridian, in order to observe the transit of Venus, I rashly directed to the sun, by my right eye, the cross hairs of a small telescope. I had often done the like in my younger days with impunity ; but I suffered by it at last, which I mention as a warning to others. I soon observed a remarkable dimness in that eye; and for many weeks, when I was in the dark, or shut my eyes, there appeared before the right eye a lucid spot, which trembled much like the image of the sun seen by reflection from water. This appearance grew fainter, and less frequent, by degrees ; so that now there are seldom any remains of it. But some other very sensible effects of this hurt still remain. For, First, The sight of the right eye continues to be more dim than that of the left. Secondly, The nearest limit of distinct vision is more remote in the right eye than in the other ; al- though, before the time mentioned, they were equal in both these respects, as I had found by many trials. But, thirdly, what I chiefly intended to mention is, That a straight line, in some circumstances, appears to the right eye to have a curvature in it. Thus, when I look upon a music book, and, shutting my left eye, direct the right to a point of the middle line of the five which compose 238 THE PHILOSOPHY OF REID. [Cn. VI. the staff of music, the middle line appears dim, indeed, at the point to which the eye is directed, but straight; at the same time, the two lines above it, and the two below it, appear to be bent outwards, and to be more distant from each other and from the middle line, than at other parts of the staff, to which the eye is not directed. Fourthly, Although I have repeated this experiment times innumerable, within these sixteen months, I do not find that custom and experience takes away this ap- pearance of curvature in straight lines. Lastly, This ap- pearance of curvature is perceptible when I look with the right eye only, but not when I look with both eyes; yet I see better with both eyes together, than even with the left eye alone. I have related this fact minutely as it is, without re- gard to any hypothesis; because I think such uncommon facts deserve to be recorded. I shall leave it to others to conjecture the cause of this appearance. To me it seems most probable, that a small part of the retina toward the centre is shrunk, and that thereby the contig- uous parts are drawn nearer to the centre, and to one an- other, than they were before; and that objects whose im- ages fall on these parts, appear at that distance from each other which corresponds, not to the interval of the parts in their present preternatural contraction, but to their in- terval in their natural and sound state. Section XIII. OF SEEING OBJECTS SINGLE WITH TWO EYES. Another phaenomenon of vision which deserves atten- tion, is our seeing objects single with two eyes. There are two pictures of the object, one on each retina, and each picture by itself makes us see an object in a certain direction from the eye; yet both together commonly SEC.XIH.] THE PHILOSOPHY OF REID. 239 make us see only one object. All the accounts or solu- tions of this phenomenon given by anatomists and phi- losophers seem to be unsatisfactory. I shall pass over the opinions of Galen, of Gassendus, of Baptista Porta, and of Rohault. The reader may see these examined and refuted by Dr. Porterfield. I shall examine Dr. Porterfield's own opinion, Bishop Berkeley's, and some others. But it will be necessary first to ascertain the facts; for, if we mistake the phenomena of single and double vision, it is ten to one that this mistake will lead us wrong in assigning the causes. This likewise we ought carefully to attend to, which is acknowledged in theory by all who have any true judgment or just taste in inquiries of this nature, but is very often overlooked in practice namely, that, in the solution of natural phaenomena, all the length that the human faculties can carry us, is only this, that, from particular phaenomena, we may, by induction, trace out general phaenomena, of \ which all the particular ones are necessary consequences. . And when we have arrived at the most general phenom- ena we can reach, there we must stop. If it is asked, Why such a body gravitates towards the earth ? all the answer that can be given is, Because all bodies gravitate towards the earth. This is resolving a particular phae- nomenon into a general one. If it should again be asked, Why do all bodies gravitate toward the earth ? we can give no other solution of this phaenomenon, but that all bodies whatsoever gravitate towards each other. This is \resolving a general phaenomenon into a more general one. If it should be asked, Why all bodies gravitate to one another? we cannot tell; but, if we could tell, it could only be by resolving this universal gravitation of bodies into some other phaenomenon still more general, and of which the gravitation of all bodies is a particular instance. The most general phaenomena we can reach, are what we call laws of nature; so that the laws of na- ture are nothing else but the most general facts relating 240 THE PHILOSOPHY OF REID. [CH. VI. to the operations of nature, which include a great many particular facts under them. And if, in any case, we should give the name of a law of nature to a general phaenomenon, which human industry shall afterwards trace to one more general, there is no great harm done. The most general assumes the name of a law of nature when it is discovered, and the less general is contained and comprehended in it. Having premised these things, we proceed to consider the phenomena of single and double vision, in order to discover some general princi- ple to which they all lead, and of which they are the necessary consequences. If we can discover any such general principle, it must either be a law of nature, or the necessary consequence of some law of nature; and its authority will be equal whether it is the first or the last. 1. We find that, when the eyes are sound and perfect, and the axes of both directed to one point, an object placed in that point is seen single and here we observe, that in this case the two pictures which shew 4 the object single, are in the centres of the retina. When two pict- ures of a small object are formed upon points of the retina, if they shew the objects single, we shall, for the sake of perspicuity, call such two points of the retina, corresponding points; and where the object is seen double, we shall call the points of the retina on which the pict- ures are formed, points that do not correspond. Now, in this first phsenomenon, it is evident, that the two centres of the retina are corresponding points. 2. Supposing the same things as in the last phenomenon, other objects at the same distance from the eyes as that to which their axes are directed, do also appear single. Thus, if I direct my eyes to a candle placed at the distance of ten feet, and, while I look at this candle, another stands at the same distance from my eyes, within the field of vision, I can, while I look at the first candle, attend to the ap- pearance which the second makes to the eye; and I find SEC. XIII.) THE PHILOSOPHY OF REID. 241 that in this case it always appears single. It is here to be observed, that the pictures of the second candle do not fall upon the centres of the retince, but they both fall upon the same side of the centres that is, both to the right, or both to the left; and both are at the same distance from the centres. This might easily be demonstrated from the principles of optics. Hence it appears, that in this second phenomenon of single vision, the corresponding points are points of the two retin-ce, which are similarly situate with respect to the two centres, being both upon the same side of the centre, and at the same distance from it. It appears likewise, from this phenomenon, that every point in one retina corresponds with that which is similarly situate in the other. 3. Supposing still the same things, objects which are much nearer to the eyes, or much more distant from them, than that to which the two eyes are directed, appear double. Thus, if the candle is placed at the distance of ten feet, and I hold my finger at arms- length between my eyes and the candle when I look at the candle, I see my finger double; and when I look at my finger, I see the candle double; and the same thing happens with regard to all other objects at like distances which fall within the sphere of vision. In this phsenom- enon, it is evident to those who understand the princi- ples of optics, that the pictures of the objects which are seen double, do not fall upon the points of the retince which are similarly situate, but that the pictures of the objects seen single, do fall upon points similarly situate. Whence we infer, that, as the points of the two retina, which are similarly situate with regard to the centres, do correspond, so those which are dissimilarly situate do not correspond. 4. It is to be observed, that, although, in such cases as are mentioned in the last phaenomenon, we have been accustomed from infancy to see objects double which 242 THE PHILOSOPHY OF REID. [H. VI. we know to be single; yet custom, and experience of the unity of the object, never take away this appearance of duplicity. 5. It may, however, be remarked that the custom of attending to visible appearances has a considerable ef- fect, and makes the phenomenon of double vision to be more or less observed and remembered. Thus you may find a man that can say, with a good conscience, that he never saw things double all his life; yet this very man, put in the situation above mentioned, with his finger be- tween him and the candle, and desired to attend to the appearance of the object which he does not look at, will, upon the first trial, see the candle double, when he looks at his finger; and his finger double, when he looks at the candle. Does he now see otherwise than he saw before? No; surely; but he now attends to what he never attended to before. The same double appearance of an object hath been a thousand times presented to his eye before now, but he did not attend to it; and so it is as little an object of his reflection and memory, as if it had never happened. When we look at an object, the circumjacent objects may be seen at the same time, although more obscurely and indistinctly: for the eye hath a considerable field of vision, which it takes in at once. But we attend only to the object we look at. The other objects which fall within the field of vision, are not attended to; and there- fore are as if they were not seen. If any of them draws our attention, it naturally draws the eyes at the same time : for, in the common course of life, the eyes always follow the attention : or if at any time, in a revery, they are separated from it, we hardly at that time see what is directly before us. Hence we may see the reason why the man we are speaking of thinks that he never before saw an object double. When he looks at any object, he sees it single, and takes no notice of other visible objects at that time, whether they appear single or double. If SEC. XIII.] THE PHILOSOPHY OF REID. 243 any of them draws his attention, it draws his eyes at the same time ; and, as soon as the eyes are turned towards it, it appears single. But, in order to see things double at least, in order to have any reflection or remembrance that he did so it is necessary that he should look at one object, and at the same time attend to the faint appear- ance of other objects which are within the field of vision. This is a practice which perhaps he never used, nor at- tempted ; and therefore he does not recollect that ever he saw an object double. But when he is put upon giv- ing this attention, he immediately sees objects double, in the same manner, and with the very same circum- stances, as they who have been accustomed, for the greatest part of their lives, to give this attention. There are many phenomena of a similar nature, which shew that the mind may not attend to, and thereby, in some sort, not perceive objects that strike the senses. I had occasion to mention several instances of this in the second chapter; and I have been assured, by persons of the best skill in music, that, in hearing a tune upon the harpsichord, when they give attention to the treble, they do not hear the bass; and when they attend to the bass, they do not perceive the air of the treble. Some persons are so near-sighted, that, in reading, they hold the book to one eye, while the other is directed to other objects. Such persons acquire the habit of attending, in this case, to the objects of one eye, while they give no attention to those of the other. 6. It is observable, that, in all cases, wherein we see an object double, the two appearances have a certain position with regard to one another, and a certain ap- parent or angular distance. This apparent distance is greater or less in different circumstances ; but, in the same circumstances, it is always the same, not only to the same, but to different persons. Thus, in the experiment above mentioned, if twenty different persons, who see perfectly with both eyes, shall 244 THE PHILOSOPHY OF REID. [Cn. VI. place their finger and the candle at the distances above expressed, and hold their heads upright, looking at the finger, they will see two candles, one on the right, another on the left. That which is seen on the right, is seen by the right eye, and that which is seen on the left, by the left eye; and they will see them at the same apparent dis- tance from each other. If, again, they look at the candle, they will see two fingers, one on the right, and the other on the left ; and all will see them at the same apparent distance ; the finger towards the left being seen by the right eye, and the other by the left. If the head is laid horizontally to one side, other circumstances remaining the same, one appearance of the object seen double, will be directly above the other. In a word, vary the cir- cumstances as you please, and the appearances are varied to all the spectators in one and the same manner. 7. Having made many experiments in order to as- certain the apparent distance of the two appearances of an object seen double, I have found that in all cases this apparent distance is proportioned to the distance between the point of the retina, where the picture is made in one eye, and the point which is situated similarly to that on which the picture is made on the other eye ; so that, as the apparent distance of two objects seen with one eye, is proportioned to the arch of the retina, which lies be- tween their pictures, in like manner, when an object is seen double with the two eyes, the apparent distance of the two appearances is proportioned to the arch of either retina, which lies between the picture in that retina, and the point corresponding to that of the picture in the other retina. 8. As, in certain circumstances, we invariably see one obect appear double, so, in others, we as invariably see two objects unite into one, and, in appearance, lose their duplicity. This is evident in the appearance of the binocular telescope. And the same thing happens when any two similar tubes are applied to the two eyes in a SEC. XIII.] THE PHILOSOPHY OF REID. 245 parallel direction; for, in this case, we see only one tube. And if two shillings are placed at the extremities of the two tubes, one exactly in the axis of one eye, and the other in the axis of the other eye, we shall see but one shilling. If two pieces of coin, or other bodies, of dif- ferent colour, and of different figure be properly placed in the two axes of the eyes, and at the extremities of the tubes, we shall see both the bodies in one and the same place, each as it were spread over the other, without hid- ing it ; and the colour will be that which is compounded of the two colours. 9. From these phenomena, and from all the trials I have been able to make, it appears evidently, that, in perfect human eyes, the centres of the two retina cor- respond and harmonize with one another, and that every other point in one retina doth correspond and harmonize with the point which is similarly situate in the other- in such manner, that pictures falling on the corresponding points of the t wo retina, shew only one object, even when there are really two; and pictures falling upon points of the retina which do not correspond, shew us two visible appearances, although there be but one object: so that pictures, upon corresponding points of the two retina, present the same appearance to the mind as if they had both fallen upon the same point of one retina; and pictures upon points of the two retina, which do not correspond, present to the mind the same apparent dis- tance and position of two objects, as if one of those pictures was carried to the point corresponding to it in the other retina. This relation and sympathy between corresponding points of the two retina, I do not advance as an hypothesis, but as a general fact or phenomenon of vision. All the phaenomena before mentioned, of single or double vision, lead to it, and are necessary consequences of it. It holds true invariably in all per- fect human eyes, as far as I am able to collect from in- numerable trials of various kinds made upon my own 246 THE PHILOSOPHY OF REID. [C H . VI. eyes, and many made by others at my desire. Most of the hypotheses that have been contrived to resolve the phenomena of single and double vision, suppose this general fact, while their authors were not aware of it. Sir Isaac Newton, who was too judicious a philosopher, and too accurate an observer, to have offered even a conjecture which did not tally with the facts that had fallen under his observation, proposes a query with re- spect to the cause of it ' ' Optics, " Query, 1 5. The judi- cious Dr. Smith, in his "Optics," Book I, 137, hath confirmed the truth of this general phenomenon from his own experience, not only as to the apparent unity of objects whose pictures fall upon the corresponding points of the retince, but also as to the apparent distance of the two appearances of the same object when seen double. This general phaenomenon appears, therefore, to be founded upon a very full induction, which is all the evi- dence we can have for a fact of this nature. Before we make an end of this subject, it will be proper to inquire, First, Whether those animals whose eyes have an adverse position in their heads, and look contrary ways, have such corresponding points in their retina? Secondly, What is the position of the corresponding points in im- perfect human eyes I mean in those that squint ? And, in the last place, Whether this harmony of the corre- sponding points in the retince, be natural and original, or the effect of custom ? And, if it is original, Whether it can be accounted for by any of the laws of nature al- ready discovered ? or whether it is itself to be looked upon as a law of nature, and a part of the human con- stitution ? Section XIV. OF THE LAWS OF VISION IN BRUTE ANIMALS. It is the intention of nature, in giving eyes to animals, that they may perceive the situation of visible objects, or the direction in which they are placed it is probable, SEC. XIV.] THE PHILOSOPHY OF REID. 247 therefore, that, in ordinary cases, every animal, whether it has many eyes or few, whether of one structure or of another, sees objects single, and in their true and pro- per direction. And, since there is a prodigious variety in the structure, the motions, and the number of eyes in different animals and insects, it is probable that the laws by which vision is regulated, are not the same in all, but various, 'adapted to the eyes which nature hath given them. Mankind naturally turn their eyes always the same way, so that the axes of the two eyes meet in one point. They naturally attend to, or look at that object only which is placed in the point where the axes meet. And whether the object be more or less distant, the configu- ration of the eye is adapted to the distance of the object, so as to form a distinct picture of it. When we use our eyes in this natural way, the two pictures of the object we look at are formed upon the centres of the two retince; and the two pictures of any contiguous object are formed upon the points of the retince which are similarly situate with regard to the centres. Therefore, in order to our seeing objects single, and in their proper direction, with two eyes, it is suffi- cient that we be so constituted, that objects whose pictures are formed upon the centres of the two retince, or upon points similarly situate with regard to these centres, shall be seen in the same visible place. And this is the con- stitution which nature hath actually given to human eyes. When we distort our eyes from their parallel direction, which is an unnatural motion, but may be learned by practice; or when we direct the axes of the two eyes to one point, and at the same time direct our attention to some visible object much nearer or much more distant than that point, which is also unnatural, yet may be learned : in these cases, and in these only, we see one ob- ject double, or two objects confounded in one. In these 248 THE PHILOSOPHY OF REID. [CH. VI. cases, the two pictures of the same object are formed upon points of the retina which are not similarly sit- uate, and so the object is seen double; or the two pic- tures of different objects are formed upon points of the refines which are similarly situate, and so the two ob- jects are seen confounded in one place. Thus it appears, that the laws of vision in the human constitution are wisely adapted to the natural use of human eyes, but not to that use of them which is un- natural. We see objects truly when we use our eyes in the natural way; but have false appearances presented to us when we use them in a way that is unnatural. We may reasonably think that the case is the same with other animals. But is it not unreasonable to think, that those animals which naturally turn one eye towards one object, and another eye towards another object, must thereby have such false appearances presented to them, as we have when we do so against nature ? Many animals have their eyes by nature placed ad- verse and immovable, the axes of the two eyes being always directed to opposite points. Do objects painted on the centres of the two retina appear to such animals as they do to human eyes, in one and the same visible place ? I think it is highly probable that they do not ; and that they appear, as they really are, in opposite places. If we judge from analogy in this case, it will lead us to think that there is a certain correspondence between points of the two retinas in such animals, but of a differ- ent kind from that which we have found in human eyes. The centre of one retina will correspond with the centre of the other, in such manner that the objects whose pic- tures are formed upon the secorresponding points, shall appear not to be in the same place, as in human eyes, but in opposite places. And in the same manner will the superior part of one retina correspond with the in- ferior part of the other, and the anterior part of one with the posterior part of the other. SEC. XV.] THE PHILOSOPHY OF REID. 249 Some animals, by nature, turn their eyes with equal facility, either the same way or different ways, as we turn our hands and arms. Have such animals corresponding points in their retince, and points which do not corre- spond, as the human kind has ? I think it is probable that they have not; because such a constitution in them could serve no other purpose but to exhibit false appear- ances. If we judge from analogy, it will lead us to think, that, as such animals move their eyes in a manner sim- ilar to that in which we move our arms, they have an immediate and natural perception of the direction they give to their eyes, as we have of the directions we give to our arms; and perceive the situation of visible objects by their eyes, in a manner similar to that in which we perceive the situation of tangible objects with our hands. We cannot teach brute animals to use their eyes in any other way than in that which nature hath taught them; nor can we teach them to communicate to us the appearances which visible objects make to them, either in ordinary or in extraordinary cases. We have not, therefore, the same means of discovering the laws of vision in them, as in our own kind, but must satisfy ourselves with probable conjectures; and what we have said upon this subject, is chiefly intended to shew, that animals to which nature hath given eyes differing in their number, in their position, and in their natural motions, may very probably be subjected to different laws of vision, adapted to the peculiarities of their organs of vision. Section XV. SQUINTING CONSIDERED HYPOTHETICALLY. Whether there be corresponding points in the retina, of those who have an involuntary squint ? and if there are, whether they be situate in the same manner as in 250 THE PHILOSOPHY OF REID. [CH.Vi. those who have no squint ? are not questions of mere curiosity. They are of real importance to the physician who attempts the cure of a squint, and to the patient who submits to the cure. After so much has been said of the strabismus, or squint, both by medical and by optical writers, one might expect to find abundance of facts for determining these questions. Yet, I confess, I have been disappointed in this expectation, after taking some pains both to make observations, and to collect those which have been made by others. Nor will this appear very strange, if we consider, that to make the observations which are necessary for deter- mining these questions, knowledge of the principles of optics, and of the laws of vision, must concur with opportunities rarely to be met with. Of those who squint, the far greater part have no dis- tinct vision with one eye. When this is the case, it is impossible, and indeed of no importance, to determine the situation of the corresponding points. When both eyes are good, they commonly differ so much in their direction, that the same object cannot be seen by both at the same time; and, in this case, it will be very diffi- cult to determine the situation of the corresponding points; for such persons will probably attend only to the objects of one eye, and the objects of the other will be as little regarded as if they were not seen. We have before observed, that, when we look at a near object, and attend to it, we do not perceive the double appearances of more distant objects, even when they are in the same direction, and are presented to the eye at the same time. It is probable that a squinting person, when he attends to the objects of one eye, will, in like manner, have his attention totally diverted from the objects of the other; and that he will perceive them as little as we perceive the double appearances of objects when we use our eyes in the natural way. Such a per- son, therefore, unless he is so much a philosopher as to SEC. XV.] THE PHILOSOPHY OF REID. 2$! have acquired the habit of attending very accurately to the visible appearances of objects, and even of objects which he does not look at, will not be able to give any light to the questions now under consideration. It is very probable that hares, rabbits, birds, and fishes, whose eyes are fixed in an adverse position, have the natural faculty of attending at the same time to visible objects placed in different, and even in contrary direc- tions; because, without this faculty, they could not have those advantages from the contrary direction of their eyes, which nature seems to have intended. But it is not probable that those who squint have any such natural faculty; because we find no such faculty in the rest of the species. We naturally attend to objects placed in the point where the axes of the two eyes meet, and to them only. To give attention to an object in a different direction is unnatural and not to be learned without pains and practice. A very convincing proof of this may be drawn from a fact now well known to philosophers : when one eye is shut, there is a certain space within the field of vision, where we can see nothing at all the space which is di- rectly opposed to that part of the bottom of the eye where the optic nerve enters. This defect of sight, in one part of the eye, is common to all human eyes, and hath been so from the beginning of the world; yet it was never known, until the sagacity of the Abb6 Mari- otte discovered it in the last century. And now when it is known, it cannot be perceived, but by means of some particular experiments, which require care and at- tention to make them succeed. What is the reason that so remarkable a defect of sight, common to all mankind, was so long unknown, and is now perceived with so much difficulty ? It is surely this That the defect is at some distance from the axis of the eye, and consequently in a part of the field of vision to which we never attend naturally, and to 2$2 THE PHILOSOPHY OF REID. [CH. VI. which we cannot attend at all, without the aid of some particular circumstances. From what we have said, it appears, that, to deter- mine the situation of the corresponding points in the eyes of those who squint, is impossible, if they do not see distinctly with both eyes; and that it will be very difficult, unless the two eyes differ so little in their di- rection, that the same object may be seen with both at the same time. Such patients I apprehend are rare; at least there are very few of them with whom I have had the fortune to meet: and therefore, for the assistance of those who may have happier opportunities, and inclina- tion to make the proper use of them, we shall consider the case of squinting, hypothetically, pointing out the proper articles of inquiry, the observations that are wanted, and the conclusions that may be drawn from them. 1. It ought to be inquired, Whether the squinting person sees equally well with both eyes ? and, if there be a defect in one, the nature and degree of that defect ought to be remarked. The experiments by which this may be done, are so obvious, that I need not mention them. But I would advise the observer to make the proper experiments, and not to rely upon the testimony of the patient; because I have found many instances, both of persons that squinted, and others who were found, upon trial, to have a great defect in the sight of one eye, although they were never aware of it before. In all the following articles, it is supposed that the patient sees with both eyes so well as to be able to read with either, when the other is covered. 2. It ought to be inquired, Whether, when one eye is covered, the other is turned directly to the object ? This ought to be tried in both eyes successively. By this observation, as a touchstone, we may try the hy- pothesis concerning squinting, invented by M. de la Hire, and adopted by Boerhaave, and many others of the medical faculty. SEC. XV.] THE PHILOSOPHY OF REID. 2$3 The hypothesis is, That, in one eye of a squinting person, the greatest sensibility and the most distinct vision is not, as in other men, in the centre of the retina, but upon one side of the centre ; and that he turns the axis of this eye aside from the object, in order that the picture of the object may fall upon the most sensible part of the retina, and thereby give the most distinct vision. If this is the cause of squinting, the squinting eye will be turned aside from the object, when the other eye is covered, as well as when it is not. A trial so easy to be made, never was made for more than forty years ; but the hypothesis was very generally received so prone are men to invent hypotheses, and so backward to examine them by facts. At last, Dr. Jurin having made the trial, found that persons who squint turn the axis of the squinting eye directly to the object, when the other eye is covered. This fact is confirmed by Dr. Porterfield ; and I have found it verified in all the in- stances that have fallen under my observation. 3. It ought to be inquired, Whether the axes of the two eyes follow one another, so as to have always the same inclination, or make the same angle, when the person looks to the right or to the left, upward or down- ward, or straight forward. By this observation we may judge whether a squint is owing to any defect in the muscles which move the eye, as some have supposed. In the following articles, we suppose that the inclination of the axes of the eyes is found to be always the same. 4. It ought to be inquired, Whether the person that squints sees an object single or double I If he sees the object double, and if the two appear- ances have an angular distance, equal to the angle which the axes of his eyes make with each other, it may be con- cluded that he hath corresponding points in the retince of his eyes, and that they have the same situation as in those who have no squint If the two appearances should 254 THE PHILOSOPHY OF REID. |Cn. VI. have an angular distance which is always the same, but manifestly greater or less than the angle contained under the optic axes, this would indicate corresponding points in the retina, whose situation is not the same as in those who have no squint ; but it is difficult to judge accurately of the angle which the optic axes make. A squint too small to be perceived, may occasion double vision of objects : for, if we speak strictly, every person squints more or less, whose optic axes do not meet exactly in the object which he looks at. Thus, if a man can only bring the axes of his eyes to be parallel, but cannot make them converge in the least, he must have a small squint in looking at near objects, and will see them double, while he sees very distant objects single. Again, if the optic axes always converge, so as to meet eight or ten feet before the face at farthest, such a person will see near objects single ; but when he looks at very distant objects, he will squint a little, and see them double. An instance of this kind is related by Aguilonius in his "Optics," who says, that he had seen a young man to whom near objects appeared single, but distant objects appeared double. Dr. Briggs, in his " Nova Visionis Theoria," having col- lected from authors several instances of double vision, quotes this from Aguilonius, as the most wonderful and unaccountable of all, insomuch that he suspects some im- position on the part of the young man: but to those who understand the laws by which single and double vision are regulated, it appears to be the natural effect of a very small squint. Double vision may always be owing to a small squint, when the two appearances are seen at a small angular distance, although no squint was observed : and I do not remember any instances of double vision recorded by authors, wherein any account is given of the angular dis- tance of the appearances. SEC. XV.] THE PHILOSOPHY OF REID. 2$$ In almost all the instances of double vision, there is reason to suspect a squint or distortion of the eyes, from the concomitant circumstances, which we find to be one or other of the following the approach of death or of a deliquium, excessive drinking or other intemperance, vio- lent headache, blistering the head, smoking tobacco, blows or wounds in the head. In all these cases, it is reasonable to suspect a distortion of the eyes, either from spasm, or paralysis in the muscles that move them. But, although it be probable that there is always a squint greater or less where there is double vision, yet it is certain that there is not double vision always where there is a squint. I know no instance of double vision that continued for life, or even for a great number of years. . We shall therefore suppose, in the following arti- cles, that the squinting person sees objects single. 5. The next inquiry, then, ought to be, Whether the object is seen with both eyes at the same time, or only with the eye whose axes is directed to it ? It hath been taken for granted, by the writers upon the strabismus, be- fore Dr. Jurin, that those who squint commonly see ob- jects single with both eyes at the same time ; but I know not one fact advanced by any writer which proves it. Dr. Jurin is of a contrary opinion ; and, as it is of conse- quence, so it is very easy, to determine this point, in particular instances, by this obvious experiment. While the person that squints looks steadily at an object, let the observer carefully remark the direction of both his eyes, and observe their motions ; and let an opaque body be interposed between the object and the two eyes succes- sively. If the patient, notwithstanding this interposition, and without changing the direction of his eyes, continues to see the object all the time, it may be concluded that he saw it with both eyes at once. But, if the interposi- tion of the body between one eye and the object makes it disappear, then we may be certain that it was seen by that eye only. In the two following articles, we shall 256 THE PHILOSOPHY OF REID. |CH. VI. suppose the first to happen, according to the common hypothesis. 6. Upon this supposition, it ought to be inquired, Whether the patient sees an object double in those cir- cumstances wherein it appears double to them who have no squint? Let him, for instance, place a candle at the distance of ten feet ; and holding his finger at arm's- length between him and the candle, let him observe, when he looks at the candle, whether he sees his finger with both eyes, and whether he sees it single or double; and when he looks at his finger, let him observe whether he sees the candle with both eyes and whether single or double. By this observation, it may be determined, whether to this patient, the phenomena of double as well as of sin- gle vision are the same as to them who have no squint. If they are not the same if he sees objects single with two eyes, not only in the cases wherein they appear sin- gle, but in those also wherein they appear double to other men the conclusion to be drawn from this supposition is, that his single vision does not arise from corresponding points in the retina of his eyes : and that the laws of vis- ion are not the same in him as in the rest of mankind. 7. If, on the other hand, he sees objects double in those cases wherein they appear double to others, the conclusion must be, that he hath corresponding points in the retina of his eyes, but unnaturally situate. And their situation may be thus determined. When he looks at an object, having the axis of one eye directed to it, and the axis of the other turned aside from it, let us suppose a right line to pass from the object through the centre of the diverging eye. We shall, for the sake of perspicuity, call this right line, the natural axis of the eye ; and it will make an angle with the real axis, greater or less, according as his squint is greater or less. We shall also call that point of the retina in which the natural axis cuts it, the natural centre of the retina ; which will SEC. XV.] THE PHILOSOPHY OF REID. 257 be more or less distant from the real centre, according as the squint is greater or less. Having premised these definitions, it will be evident to those who understand the principles of optics, that in this person the natural centre of one retina corresponds with the real centre of the other, in the very same man- ner as the two real centres correspond in perfect eyes ; and that the points similarly situate with regard to the real centre in one retina, and the natural centre in the other, do likewise correspond, in the very same manner as the points similarly situate with regard to the two real cen- tres correspond in perfect eyes. If it is true, as has been commonly affirmed, that one who squints sees an object with both eyes at the same time, and yet sees it single, the squint will most probably be such as we have described in this article. And we may further conclude, that, if a person affected with such a squint as we have supposed, could be brought to the habit of looking straight, his sight would thereby be greatly hurt ; for he would then see everything double which he saw with both eyes at the same time ; and ob- jects distant from one another would appear to be con- founded together. His eyes are made for squinting, as much as those of other men are made for looking straight; and his sight would be no less injured by looking straight, than that of another man by squinting. He can never see perfectly when he does not squint, unless the corre- sponding points of his eyes should by custom change their place ; but how small the probability of this is will appear in the i yth section. Those of the medical faculty who attempt the cure of a squint, would do well to consider whether it is attended with such symptoms as are above described. If it is, the cure would be worse than the malady: for, everyone will readily acknowledge that it is better to put up with the deformity of a squint, than to purchase the cure by the loss of perfect and distinct vision. 258 THE PHILOSOPHY OF REID. [Cn. VI. 8. We shall now return to Dr. Jurin's hypothesis, and suppose that our patient, when he saw objects single notwithstanding his squint, was found, upon trial, to have seen them only with one eye. We would advise such a patient to endeavor, by re- peated efforts, to lessen his squint, and to bring the axes of his eyes nearer to a parallel direction. We have natu- rally the power of making small variations in the inclina- tion of the optic axes ; and this power may be greatly in- creased by exercise. In the ordinary and natural use of our eyes, we can direct their axes to a fixed star; in this case they must be parallel: we can direct them also to an object six inches distant from the eye; and in this case the axes must make an angle of fifteen or twenty degrees. We see young people in their frolics learn to squint, making their eyes either converge or diverge, when they will, to a very considerable degree. Why should it be more difficult for a squinting person to learn to look straight when he pleases? If once, by an eifort of his will, he can but lessen his squint, frequent practice will make it easy to lessen it, and will daily increase his power. So that, if he begins this practice in youth, and perseveres in it, he may probably, after some time, learn to direct both his eyes to one object. When he hath acquired this power, it will be no diffi- cult matter to determine, by proper observations, whether the centres of the retina, and other points similarly sit- uate with regard to the centres, correspond, as in other men. 9. Let us now suppose that he finds this to be the case ; and that he sees an object single with both eyes, when the axes of both are directed to it. It will then concern him to acquire the habit of looking straight, as he hath got the power, because he will thereby not only remove a deformity, but improve his sight ; and I con- ceive this habit, like all others, may be got by frequent SEC. XV.] THE PHILOSOPHY OF REID. 259 exercise. He may practise before a mirror when alone, and in company he ought to have those about him who will observe and admonish him when he squints. 10. What is supposed in the 9th article is not merely imaginary ; it is really the case of some squinting per- sons, as will appear in the next section. Therefore, it ought further to be inquired, How it comes to pass that such a person sees an object which he looks at, only with one eye, when both are open ? In order to answer this question, it may be observed, first, Whether, when he looks at an object, the diverging eye is not drawn so close to the nose, that it can have no distinct images ? Or, secondly, whether the pupil of the diverging eye is not covered wholly, or in'part, by the upper eyelid ? Dr. Jurin observed instances of these cases in persons that squinted, and assigns them as causes of their seeing the object only with one eye. Thirdly, it may be observed, whether the diverging eye is not so directed, that the picture of the object falls upon that part of the retina where the optic nerve enters, and where there is no vision ? This will probably happen in a squint wherein the axes of the eyes converge so as to meet about six inches before the nose. 11. In the last place, it ought to be inquired, Whether such a person hath any distinct vision at all with the di- verging eye, at the time he is looking at an object with the other ? It may seem very improbable that he should be able to read with the diverging eye when the other is covered, and yet, when both are open, have no distinct vision with it at all. But this, perhaps, will not appear so improb- able if the following considerations are duly attended to. Let us suppose that one who saw perfectly, gets, by a blow on the head, or some other accident, a perma- nent and involuntary squint. According to the laws of vision, he will see objects double, and will see objects distant from one another confounded together ; but, such vision being very disagreeable, as well as incon- 260 THE PHILOSOPHY OF REID. [Ca. VI. venient, he will do everything in his power to remedy it. For alleviating such distresses, nature often teaches men wonderful expedients, which the sagacity of a philoso- pher would be unable to discover. Every accidental motion, every direction or conformation of his eyes, which lessens the evil, will be agreeable ; it will be re- peated until it be learned to perfection, and become ha- bitual, even without thought or design. Now, in this case, what disturbs the sight of one eye is the sight of the other ; and all the disagreeable appearances in vision would cease if the light of one eye was extinct. The sight of one eye will become more distinct and more agreeable, in the same proportion as that of the other becomes faint and indistinct. It may, therefore, be ex- pected, that every habit will, by degrees, be acquired which tends to destroy distinct vision in one eye while it is preserved in the other. These habits will be greatly facilitated if one eye was at first better than the other ; for, in that case, the best eye will always be directed to the object which he intends to look at, and every habit will be acquired which tends to hinder his seeing it at all, or seeing it distinctly by the other at the same time. I shall mention one or two habits that may probably be acquired in such a case ; perhaps there are others which we cannot so easily conjecture. First, By a small increase or diminution of his squint, he may bring it to correspond with one or other of the cases mentioned in the last article. Secondly, The diverging eye may be brought to such a conformation as to be extremely short-sighted, and consequently to have no distinct vision of objects at a distance. I knew this to be the case of one person that squinted ; but cannot say whether the short-sightedness of the diverging eye was original, or acquired by habit. We see, therefore, that one who squints, and originally saw objects double by reason of that squint, may acquire such habits that, when he looks at an object, he shall see SEC. XVI.] THE PHILOSOPHY OF REID. 26l it only with one eye ; nay, he may acquire such habits that, when he looks at an object with his best eye, he shall have no distinct vision with the other at all. Whether this is really the case being unable to deter- mine in the instances that have fallen under my observa- tion I shall leave to future inquiry. I have endeavoured, in the foregoing articles, to de- lineate such a process as is proper in observing the phae- nomena of squinting. I know well by experience, that this process appears more easy in theory than it will be found to be in practice; and that, in order to carry it on with success, some qualifications of mind are neces- sary in the patient, which are not always to be met with. But, if those who have proper opportunities and incli- nation to observe such phenomena, attend duly to this process, they may be able to furnish facts less vague and uninstructive than those we meet with, even in authors of reputation. ' By such facts, vain theories may be ex- ploded, and our knowledge of the laws of nature, which regard the noblest of our senses, enlarged. Section XVI. FACTS RELATING TO SQUINTING. Having considered the phenomena of squinting, hypothetically, and their connection with correspond- ing points in the retince. I shall now mention the facts I have had occasion to observe myself, or have met with in authors, that can give any light to this subject. Having examined above twenty persons that squinted, I found in all of them a defect in the sight of one eye. Four only had so much of distinct vision in the weak eye, as to be able to read with it, when the other was cov- ered. The rest saw nothing at all distinctly with one eye. Dr. Porterfield says, that this is generally the case of 262 THE PHILOSOPHY OF REID. tCH. VI. people that squint ; and I suspect it is so more generally than is commonly imagined. Dr. Jurin, in a very judi- cious dissertation upon squinting, printed in Dr. Smith's ''Optics/' observes, that those who squint, and see with both eyes, never see the same object with both at the same time ; that, when one eye is directed straight for- ward to an object, the other is drawn so close to the nose that the object cannot at all be seen by it, the images being too oblique and too indistinct to affect the eye. In some squinting persons, he observed the diverging eye drawn under the upper eyelid, while the other was directed to the object. From these observations, he concludes that " the eye is thus distorted, not for the sake of seeing better with it, but rather to avoid seeing at all with it as much as possible." From all the ob- servations he had made, he was satisfied that there is nothing peculiar in the structure of a squinting eye; that the fault is only in its wrong direction ; and that this wrong direction is got by habit. Therefore, he proposes that method of cure which we have described in the eighth and ninth articles of the last section. He tells us, that he had attempted a cure, after this method, upon a young gentleman, with promising hopes of suc- cess ; but was interrupted by his falling ill of the small- pox, of which he died. It were to be wished that Dr. Jurin had acquainted us whether he ever brought the young man to direct the axes of both eyes to the same object, and whether, in that case, he saw the object single, and saw it with both eyes ; and that he had likewise acquainted us, whether he saw ob- jects double when his squint was diminished. But as to these facts he is silent. I wished long for an opportunity of trying Dr. Jurin's method of curing a squint, without finding one ; having always, upon examination, discovered so great a defect in the sight of one eye of the patient as discouraged the attempt. SEC. XVI.] THE PHILOSOPHY OF REID. 263 But I have lately found three young gentlemen, with whom I am hopeful this method may have success, if they have patience and perseverance in using it. Two of them are brothers, and, before I had access to ex- amine them, had been practising this method by the di- rection of their tutor, with such success, that the elder looks straight when he is upon his guard ; the younger can direct both his eyes to one object ; but they soon return to their usual squint. A third young gentleman, who had never heard of this method before, by a few days' practice, was able to di- rect both his eyes to one object, but could noj; keep them long in that direction. All the three agree in this, that, when both eyes are directed to one object, they see it and the adjacent objects single ; but, when they squint, they see objects sometimes single and sometimes double. I observed of all the three, that when they squinted most that is, in the way they had been accustomed to the axes of their eyes converged so as to meet five or six inches before the nose. It is probable that, in this case, the picture of the object in the diverging eye, must fall upon that part of the retina where the optic nerve enters; and therefore, the object could not be seen by the eye. All the three have some defect in the sight of one eye, which none of them knew until I put them upon making trials; and when they squint, the best eye is always directed to the object, and the weak eye is that which diverges from it. But when the best eye is covered, the weak eye is turned directly to the object. Whether this defect of sight in one eye, be the effect of its having been long disused, as it must have been when they squinted; or whether some original defect in one eye might be the occasion of their squinting, time may discover. The two brothers have found the sight of the weak eye im- proved by using to read with it while the other is covered. The elder can read an ordinary print with the weak eye the other, as well as the third gentleman, can only read 264 THE PHILOSOPHY OF REID. [Cn. VL a large print with the weak eye. I have met with one other person only who squinted, and yet could read a large print with the weak eye. He is a young man, whose eyes are both tender and weak-sighted, but the left much weaker than the right. When he looks at any object, he al- ways directs the right eye to it, and then the left is turned towards the nose so much that it is impossible for him to see the same object with both eyes at the same time. When the right eye is covered, he turns the left directly to the object; but he sees it indistinctly, and as if it had a mist about it. I made several experiments, some of them in the com- pany and with the assistance of an ingenious physician, in order to discover whether objects that were in the axes of the two eyes, were seen in one place confounded to- gether, as in those who have no involuntary squint. The object placed in the axis of the weak eye was a lighted candle, at the distance of eight or ten feet. Before the other eye was placed a printed book, at such a distance as that he could read upon it. He said, that while he read upon the book, he saw the candle but very faintly. And from what we could learn, these two objects did not appear in one place, but had all that angular dis- tance in appearance which they had in reality. If this was really the case, the conclusion to be drawn from it is, that the corresponding points in his eyes are not situate in the same manner as in other men; and that, if he could be brought to direct both eyes to one object, he would see it double. But, considering that the young man had never been accustomed to observa- tions of this kind, and that the sight of one eye was so imperfect, I do not pretend to draw this conclusion with certainty from this single instance. All that can be inferred from these facts is, that, of four persons who squint, three appear to have nothing preternatural in the structure of their eyes. The cen- tres of their r$tin 335 I definition of the soul, 342-3 ; referred to, 344; materialistic ten- dency of his system, 346. Association of ideas, 332-3. Bacon, his services, 334. Belief, Locke's theory of, criticised, 95 sq.; Hume's theory of, criticised, 96 sq., 330 ; cannot be defined, 96 sq. ; in human testi- mony, 323 sq.; in the con- tinuance of the present course of nature, 328 sq.; an ingredient of mental operations, 137 sq., 228, 330. Berkeley, relation of his philosophy to scepticism, 81 sq., 86 sq., 349, 353 ; ideas and spirits, 102, 186; natural signs, 139 H. ; pri- mary and secondary qual- ities of matter, 140 ; qual- ities of matter not resem- bling sensations, 138 sq., J 53> r 58; his solution of certain phenomena of vi- sion examined, 218, 220 sq. ; noticed, 148, 160, 186, 199 H., 267, 272, 310, 312, 316, 345. Body, its qualities, how ap- prehended, 181 sq. Borrichius, 210. Brain, 223, 224. Briggs, Dr., 254, 279. Caesalpinus, 284. Cause and effect, 332. Cheselden, case of couch- ing, 172, 194, 271 sq.; on double vision, 270. Cold, I29sq. ; see Touch. Color, 162 sq. ; see Seeing; a blind man's notion of, 165 sq. Common sense, the root of all philosophy, 81 ; prin- ciples of, 100, 358 ; prac- tically acknowledged by the idealists, 104 ; con- trasted with the ideal phi- losophy, 132 sq., 358. 363 364 INDEX. Conception, distinguished from perception, 289 H. Consciousness, Des Cartes' view of, 345 H., 350. Credulity, 325. Custom, 265 sq. Democritus, on the qualities of matter, 140, 157, 180, i8oH. Des Cartes, his doubt, 77, 345 ; misapprehended by Reid, 77 H.; scepticism the natural issue of his system, 86 sq., 349; on primary and secondary qualities, 140, 157 ; on seeing objects erect by in- verted images, 215, 216 ; the father of the new philosophy of mind, 341 ; remarks upon the Car- tesian system, 345 sq. ; no- ticed, 72, 82, 84, 103, 148, 154, 155 H., 1 60, 184. Dimerbroeck, 284. Distance, how computed by the eye, 304 sq. Divine veracity, 155 H. Effluvia, 90. 343. Epicurus and the Epicu- reans, on primary and secondary qualities, 140, 157, 180.; theory of per- ception, 344. Experience, 323. Experiment, 71. Extension, notion of, 141-7, 18791; see Seeing, Sight, Touch; Reid's and Kant's theories contrasted, 141 H.; possibility of an a posteriori perception of, 147 H. Eyes, parallel motion of, 211 sq., 265 sq. ; concen- tration on one object, 263 sq. ; see Seeing. Fabricius, 210. Fichte, idealism, 152 H. Figure, how perceived by the eye, 315. Folkes, Martin, 269. Foster, case of, 269, 270. Galen, 239. Gassendi, 239. Genius, adulterates phil^so- phy, 76. Geometry of visibles, 199 sq. ; see Seeing. Grew, Dr. N., 121. Halley, Dr., 165. Hardness, 131, 139 sq.; see Touch. Hearing, 122 sq. Heat, 129 ; see Touch, Hobbes, on imagination, 182 H.; noticed, 84. Hume, his Treatise of Hu- man Nature considered, 8isq.; reduces Berkeley's system to scepticism, 86, 353; his theory of belief examined, 96 sq., 330; his theory of mind, 100 sq. ; confession, 135, 358 H.; noticed, 139, 150, 160, 184, 186, 345, 349 H, 356. Idea, how used by Reid, 93-4; by Des Cartes, 351, 360. Idealism, 151-2 H. Ideal philosophy, 87 ; the theory of sensation, mem- ory, belief, and imagina- tion introduced by it con- sidered, 96; psychological history of, 100 sq. ; re- marks on, 153 sq. Ideas, doctrines of ancient philosophers about, 343 sq. Identity, Locke's account of, considered, 79. Image, Reid's use of the term, 93. Imagination, how accom- panied, 93 H.; view of INDEX. 365 Aristotle and Hobbes, 182 H.; distinguished from perception, 289 H. Impressions, in reference to sensations, 298 sq. ; on the mind, the peripatetic theory of, 347. Inductive principle, 328 sq. Instinct, instinctive beliefs, 291 sq. ; belief in the con- stancy of nature, see In- ductive principle. Jacobi, on perception, 302 H . Jurin, Dr., Kant, relation to Hume, 66 H.; held the notion of ex- tension to be a priori, 141 H., 147 H. Kepler, on seeing objects erect by inverted images, 215, 216. Laertius, 83. Language, imperfection of, impediment to the study of mind, 74 sq.; natural, etc., considered, 124-8, 136- Laws of nature, their char- acter, 225, 230 sq., 239 sq. ; belong to mind as well as to matter, 225. Light, 162; see Seeing. Locke, his theory of person- al identity considered, 79; his definition of knowl- edge criticised, 97 sq.; quoted, 152; his doctrine of primary and secondary qualities discussed, 157, 179, 185; not the origina- tor of these terms, 185 H. ; misinterpreted by Reid, 347 H. ; noticed, '79, 82, 103, 148, 160. Lucretius, 344. Malebranche, his doctrine of primary and secondary qualities, 140, 157, 184, 186; his theory of per- ception, 343-4; noticed, 79, 82, 103, 148, 160. Mariotte, 251. Memory distinguished from perception, 330; denned, 94- Metaphysic, 88. Mind, importance of the study of, 70; how to be studied, 71, 72; impedi- ments to our knowledge of, 72-6; the systems of Des Cartes, Malebranche, and Locke, considered, 76-80; of Berkeley and Hume, 8 1-6; its exist- ence, how inferred, 105 sq.; in sensation, act- ive or passive?, 116-17; operations of, two ways of treating, 338; names of operations borrowed from sensible images, 341. Nature, the works of, 85; our belief in the uniform- ity of, 328 sq. Nerves, theory of, 279. Newton, Sir Isaac, his reg- ular philosophy, 71; on color, etc., 119; his query on single vision, 246, 282; attracting and repelling forces, 218, 350; followed Bacon's rules of inductive reasoning, 335; concerning species, 360; noticed, 113, 162, 351. Optic nerve, 222, 336, 279. Perception, in general, 287- 303; distinguished from sensation, 288, 298; law of the manifestation of sensation and perception, 287 H.; distinguished from imagination, 289, 289 H.; from memory, 289; what it implies, 289; 3 66 INDEX. original and acquired, 293 sq. ; involves no ex- ercise of reason, 295; per- ception of objects, the re- sult of what, 297-303; the true object of, im- mediate, 298 H.; analo- gous to testimony, 320-37. Peripatetics, on species, 344; their tendency to materialize mind, 346; noticed, 183, 187. Phantasms, 344. Philosophers, their notions concerning the soul, 341. Plato, his system of ideas, 343 sq.; noticed, 104. Platonists, their notion of the soul, 344. Porta, Baptista, 239. Porterfield, Dr., on vision, 226, 231 239, 253, 261, 272 sq. Pyrrho, the Elean, 83. Qualities, primary and sec- ondary, the distinction of, 140, 157, iSssq.; i8sH. Reason, in connection with common sense, 79 sq., 149; inaccurate use of term by Reid, 79 H., 149 H.; in relation to our be- lief in testimony, 327. Reflection, 338; Locke's ac- count of, 355-6. Retina, how rays of light affect, 194-237; see See- ing; how objects fall upon, 240. Rousseau, 336-7. Saunderson, N., 145, 165, 188, 220. Scepticism, in philosophy of Des Cartes, Malebranche, Locke, and Berkeley, 82, 86 sq., 349 sq. ; animad- verted on, 290; origin of, 35I-2- Scheiner, experiments ort the eye, 231. Seeing, in general, 162 sq.; color, 173-81; visible figure and extension, 187- 91; geometry of visibles, 199-211; certain phenom- ena of vision examined: the parallel motion of the eyes, our seeing objects erect by inverted images, seeing objects single with two eyes, 211 sq. Sensation, indefinable, 96; belongs to a sentient be- ing, 107; what it suggests, 106; does not resemble qualities of body, 181-7; distinguished from per- ception, 288, 298; sensa- tion and reflection as the sources of ideas, consid- ered, 354 sq. Sensations, distinguished from qualities causing them, 109 sq., 114 sq., 129 sq., 132 sq., 157, 173 sq., 177. Sense, testimony of, 320-37. Senses, systems concerning, 156-61; do not deceive, 3i9- Sensorium, defined, 222; the- ories concerning, 280-5. Sight, see Seeing. Sign, connection of, with thing signified, 135 sq. Smelling, in general, 89-116; the sensation considered abstractly, 90-2; compared with the remembrance and imagination, 92-5; as a quality in bodies, etc., 109-11; the name of smell, to what it belongs, 115-16; in sensation, the mind active or passive?, 116-17. Smith, Dr., his system of optics, 216, 246, 262, 267, 268, 269, 270, 272, 275, 279, 310, 313, 314, 316. INDEX. 367 Softness, 131 \ see Touch. Soul, opinions regarding its nature, 341 sq. Sound, see Hearing. Species, sensible, theories of, 1 80, 344. Squinting, see Seeing. Strabismus, 277. Suggestion, explained, 107 sq., 107-8 H. Taste, 118-21. Tertullian, 108 H. Testimony, evidence of, compared with that of sense, 320-37. Touch, analysed, 129 sq.; heat and cold, 129 sq. ; hardness and softness, 131 sq. ; hardness and other primary qualities, 139 sq- extension, 141 sq.; existence of a ma- terial world, 148 sq. Truth, an innate principle, 324. Valverda, 284. Vesalius, 284. Virgil, quoted, 351. Visibles, geometry of, see Seeing. Vision, see Seeing. Winslow, quoted, 284. World, material, existence of, a first principle, 148- 56, 348, 357 sq. Zeno. 84, RETURN CIRCULATION DEPART/MEN' 202 Main Library LOAN PERIOD 1 HOME USE 2 3 4 5 6 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS Renewals and Recharges may be made 4 days prior to the due date. 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