391

*Received December 2002; revised February 2003.

†To contact the author write to Department of Chemistry and Biochemistry, UCLA, 607
Charles E. Young Drive East, Los Angeles, CA 90095–1569; e-mail: scerri@chem.
ucla.edu.

Philosophy of Science, 70 (April 2003) pp. 391–398. 0031-8248/2003/7002-0010$10.00
Copyright 2003 by the Philosophy of Science Association. All rights reserved.

Response to Vollmer’s Review
of Minds and Molecules*

Eric Scerri†

I present a response to Vollmer’s review of the book Of Minds and Molecules, and
especially her comments on my own article therein. This provides an opportunity to
discuss two central ideas in the philosophy of chemistry. These are the distinction
between elements as simple substances (element-1) and elements as basic substances
(element-2) and Paneth’s proposed intermediate position for philosophy of chemistry.
The response also discusses the question of isotopes in relationship to the nature of
the elements and their classification as well as the philosophical status of atomic
orbitals.

1. While it is gratifying that the book “Minds and Molecules” has been
reviewed in this journal it is disappointing that the reviewer seems to show
a misunderstanding of most of the central issues in philosophy of chem-
istry upon which she comments (Vollmer 2003). In this brief response I
will restrict myself to Sara Vollmer’s critique of my article in this book
although I believe she is also mistaken in her comments regarding other
contributors.

Vollmer correctly reports that my article includes an analysis of Pa-
neth’s writings on the concept of an “element.” This issue concerns the
ancient conundrum of how the elements survive, if at all, when they form
compounds. Paneth resolves the conundrum by appealing to a dual sense
of the term element. An element can be regarded as a “simple substance”
that can be isolated and that can take several different structural forms,
such as diamond or graphite, in the case of carbon (Paneth 1962). Let me
call this element-1 in the interest of clarity. In addition, an element can
also be regarded, more fundamentally, as a “basic substance,” which is



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1. Although this sense of the term element may sound somewhat mysterious it should
be pointed out that it was crucial to Mendeleev’s ordering of the elements in the periodic
system. For example, if he had restricted himself to the properties in the sense of
element-1 he might not have grouped together fluorine, chlorine, bromine and iodine
which are respectively a yellow gas, a green gas, a brown liquid and a violet-black solid.

2. The issue is not one of physical mixing but chemical combination.

the bearer of properties while at the same time being devoid of properties
per se.1 This will be called element-2 in the interest of clarity.

Paneth claims that it is only the element, in the second sense, as element-
2, that survives when, for example, sodium and chlorine combine to create
sodium chloride. On the other hand, sodium and chlorine, as forms of
element-1, consist of a gray metal and a green gas respectively. These
properties clearly do not survive when sodium and chlorine, as elements-
1, combine together to form sodium chloride. Unfortunately, very little of
what Paneth or I have written on the basic substance/simple substance
distinction is even mentioned by the reviewer. Instead, Vollmer discusses
this question by claiming that it is the atoms of any element that remain
unchanged on compound formation. She is thus substituting her own ver-
sion of the question of the survival of elements in compounds, which as I
will argue is irrelevant to this discussion. Vollmer writes,

Paneth notes that the creation of a new substance by mixing2 two
known substances is prima facie incomprehensible. However, what
looks like coming into being and ceasing to be, as the atomists first
realized, can be reduced to a logic that retains an underlying, un-
changing substratum—permanent atoms. The account Paneth offers
requires, surprisingly, the existence of a strange kind of entity: the
qualityless atom. (footnote added)

In fact it is not atoms that Paneth claims to be property-less but the ele-
ments themselves. The view that atoms lack such properties as color is
held quite universally and did not need to be introduced by Paneth. It is
a scientific commonplace that atoms have no color, smell etc.

Vollmer also claims that,

What Paneth means by properties in this context are all the properties
of interest to chemists, including taste, odor, feel, color, and valence
(1965, 8). These are the properties, he says, that are generated only
by “the coming together of many atoms” and that are, therefore, not
discernible in the individual atom, such as an individual atom of gold.
(1965, 13)

Although Paneth does indeed mention earlier debates regarding whether
or not atoms have properties, this occurs in an opening historical preamble



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3. Admittedly, the move from atomic weight to atomic number is a modern develop-
ment but one that does not fundamentally alter the distinction between element-1 and
element-2. This move is discussed later in this response.

on Greek atomism and as a way of criticizing the view of Epicurus. Paneth
believes that Epicurus was wrong in emphasizing the fact that atoms are
propertyless, while maintaining that the properties of macroscopic sub-
stances are invariably real.

Epicurus rightly sought to overcome this difficulty by shifting to the
realm devoid of qualities, although in developing this idea he did not
quite arrive at our present standpoint. . . .

In principle Epicurus would have already reached the present
standpoint, had he not considered the qualities of substances to be
objectively real. Epistemologically this constitutes a step backwards
from Democritus. (Paneth 1965, 13)

For Paneth the distinction is not between one, or many, atoms but rather
between macroscopic elements in the form bearing properties (element-1)
and macroscopic elements in the form where they do not bear properties
(element-2).

Vollmer’s move to discuss the persistence of the color of elements in
terms of microscopic atoms is thus quite unwarranted although it appears
that she genuinely believes that she is referring to Paneth’s own discussion
of the persistence of the elements. But no philosophical argument for the
persistence, or otherwise, of elemental properties in compounds can be
made in terms of atoms, particularly these days, when it is generally ac-
cepted that atoms do not show properties like color.

Vollmer further misinterprets Paneth when she claims that he realized
that atomic weight explained the persistence of elements in the “wake of
Rutherford and Bohr.” In fact all that Paneth is saying, to cite him more
fully, is,

The atomic theory of Rutherford and Bohr allows us to picture par-
ticularly vividly how we are to understand the persistence of the ele-
ments in its compounds . . .” (Paneth 1962, 152 n. 3; emphasis added)

Paneth’s view on the nature of elements does not depend on the discoveries
of Rutherford and Bohr since, as he repeatedly states, it comes directly
from the view of Mendeleev, for whom the element-1/element-2 distinction
was crucial in the development of the periodic system.3 Vollmer continues,

A puzzle, then, arises. The persisting properties, which explain the
persistence of an element and therefore the identity of a chemical ele-
ment are, Paneth’s implication seems to be, properties that are not of
interest to chemists!



 394

But Paneth does not claim to have personally solved the puzzle. Through-
out his article Paneth readily concedes that his talk of the dual nature of
the elements and the resolution of the puzzle was already carried out by
the likes of Mendeleev.

Moreover, contrary to Vollmer’s statement, atomic weight is of great
interest to chemists since many of them, including Mendeleev, used it to
develop their periodic systems. Indeed atomic weight continues to be of
interest to chemists, although not for the purposes of ordering the elements
in the periodic system. The point that Paneth is making about the puzzle
of the persistence of elements is that it can be resolved provided that the
chemist ceases to be a realist but rather embraces the property-less aspect
of elements in the sense of elements-2.

2. Paneth’s Other Contribution—The Chemist’s Intermediate Position. The
far more significant contribution offered by Paneth’s paper, and some-
thing that I try to apply to the case of modern chemistry, is entirely missed
by the reviewer. Paneth’s main philosophical message is to suggest that
chemists adopt an intermediate position between what Paneth terms re-
alism and reductionism. In the case of most properties shown by elements,
Paneth contends that the chemist can afford to take a realistic attitude.
For example, the ore of mercury, called cinnabar, can be regarded as just
being red even though the chemist knows that the red color can be further
reduced to a specific range of frequencies of reflected light.

But such a form of realism, as accepting elemental properties at face
value, breaks down when the chemist is confronted with the question dis-
cussed earlier regarding the persistence of elements in compounds. In such
a case the chemist is forced to abandon the realistic view of elements, as
simple substances (element-1), and must instead maintain an anti-realistic,
or as Paneth prefers to call it, a reductionist view of elements as unob-
servable basic substances (element-2). Paneth suggests that chemists op-
erate at an intermediate position, which is neither fully realistic nor re-
ductionist, in trying to encompass these apparently different ways in which
elements behave.

It is not difficult to see why contemporary philosophers of chemistry
are interested in this idea. Paneth’s notion, and before him Mendeleev’s,
comes close to resolving the central question in modern philosophy of
chemistry, namely how to accept the findings of quantum mechanics while
still retaining the autonomy of chemistry? According to Mendeleev and
Paneth the answer lies in adopting an intermediate position between re-
garding the manifest chemical properties of elements and compounds re-
alistically, on one hand, and the reductive view from physics that tells us
that many of these properties are not in fact real, on the other hand.



   395

4. Paneth and Hevesy showed that the electrochemical potential from two cells made
from different isotopes of the metal bismuth was the same as far as experimental tech-
niques of the day could distinguish (Scerri 2000).

3. The Question of Isotopes as “Atoms.” In the 1920s Paneth drew on this
intermediate view to save the periodic system from the major crisis that it
was facing. Over a short period of time many new isotopes of the elements
were discovered, such that the number of “atoms” or most fundamental
units suddenly seemed to have multiplied. Should the periodic system con-
tinue to accommodate the traditionally regarded atoms of each element
or should it be restructured to accommodate the more elementary isotopes
of all the elements that might now be taken to constitute the true “atoms”?
Paneth’s response was that the periodic system should continue as it had
done before, in that it should accommodate the traditional chemical atoms
and not the separate isotopes of the elements. In this case the chemist
should adopt a form of naı̈ve realism by treating isotopes of the same
element as being identical, even though the physicists of the day had re-
vealed some specific differences between them.

Moreover, Paneth along with Hevesy, provided experimental evidence
in support of this choice for chemists.4 They showed that the chemical
properties of isotopes of the same element were for all intents and purposes
identical. As a result the chemist could maintain the elementary nature of
atoms of the same element even though such atoms might occur in differ-
ent isotopic forms.

It is essential to realize that in the case of this isotope controversy
Paneth’s recommendation was that the chemist should lean towards the
naive realist view and should turn a blind eye to the reductive view af-
forded by the physics of the day. This is quite unlike the case of the per-
sistence of the elements in compounds, a situation in which the chemist
must abandon realism in order to rationalize the situation.

Nowhere in my own article do I disagree with Paneth as Vollmer seems
to believe, especially not over the distinction between chemical and physi-
cal properties. For example, I do not imply that the new criterion for
identifying a basic element (element-2), namely atomic number, should be
considered as a chemical property. Atomic number is just as much a physi-
cal property as atomic weight. It just so happens that atomic number does
not discriminate between the differences in weights of the isotopes of an
element and this reflects the finding of Paneth and Hevesy that isotopes
of the same element showed identical chemical behavior.

After claiming that neither Paneth nor I have resolved the “puzzle”
Vollmer then offers her own solution which unfortunately reveals further
confusion.



 396

“Sodium,” for example, can refer to either individual Na atoms as
they exist in metallic Na (or NaCl) or to the elemental substance Na
with its metallic properties. In the former case “sodium” refers to such
properties as atomic number and weight; in the latter case, it refers to
the ordinary secondary properties of elemental sodium.

The contrast that Vollmer is trying to express is once again that of sodium
as a simple substance (element-1) that can be isolated, and is metallic, as
opposed to sodium as element-2 that lacks properties with the exception
of its atomic weight, or atomic number. Again Vollmer fails to appreciate
the correct contrast between element-1 and element-2 but now incorrectly
makes sodium, as element-1, play both roles in her supposed contrast. But
what is supposed to be the epistemological difference between “sodium in
metallic form” and “elemental sodium”?

She then continues,

One possible way to clarify our terminology would be to think of the
nuclei and inner electrons, or “kernel,” of sodium as the real sodium
itself—this is the part of sodium that is both unique to Na and persists,
more or less, through chemical change. Alternatively, “Na” could re-
fer to the entire Na atom, including its outer electrons . . .

This is a category mistake since the question is not one of the constitution
of atoms but of the nature of elements such as sodium. The question is
rather whether one should intend the term “sodium” to mean a substance
that can be isolated or whether one intends the term to mean that which
occurs in compounds like sodium chloride.

4. Vollmer on Orbitals. Vollmer’s final critique of my work concerns what
I have written about atomic orbitals. She correctly reports that I deny the
physical reality of atomic orbitals because they cannot be strictly defined
in quantum mechanics (Scerri 2001). Vollmer’s response to this is to say
that, “However . . . being well defined is not a standard condition for
reference.” She then provides what she takes to be a counter-example,
namely something that is not well defined and yet genuinely refers. Her
example is,

. . . a stellar phenomenon, if it existed long ago and far away, may be
only approximated, yet reference would not be denied on this basis.

Given that Vollmer’s example is rather vague it is difficult to know quite
how to respond. But it seems clear that she intends this stellar phenomenon
to have actually taken place at some time. If so, then whether or not we
may have an approximate knowledge of this event is an epistemological
and not an ontological question.



   397

5. I am grateful to Stathis Psillos for discussion on this point.

The case of atomic orbitals is altogether different. There are no such
objects in the world in spite of the rather misleading term that harks back
to the term “orbit” in Bohr’s old quantum theory or in astronomy. An
orbital, as opposed to an orbit, does not refer to the trajectory of an
electron. It is merely a mathematical fiction that is used to perform atomic
calculations. Atomic orbitals, unlike stellar phenomena, have no ontolog-
ical status whatsoever. The manner in which this is established is indeed
by recourse to the formalism of quantum mechanics. There is nothing in
the furniture of atomic physics that corresponds to an atomic orbital,
whereas if I understand Vollmer’s example there is no debate over whether
or not the stellar phenomenon in her example actually occurred or not.
The only issue is that the stellar phenomenon is not “well defined,” what-
ever that might mean.

I think that even a contemporary realist would be prepared to accept
that the one instance when a theoretical term should not be taken to refer
is precisely when the theory in question dictates as much.5 Of course one
could also debate whether quantum mechanics describes the world or our
knowledge of the world, that is whether it provides an ontological or an
epistemological description. But according to the Copenhagen interpre-
tation quantum mechanics provides an ontological description. The break-
down of determinism, for example, is seen as a feature of the world rather
than as some deficiency of our theoretical description. Consequently ac-
cording to the standard interpretation, atomic orbitals indeed do not exist
in the world precisely because quantum mechanics tells us so.

Of course the supporters of Bohm’s interpretation of quantum mechanics
might want to argue that the Copenhagen interpretation is actually an epis-
temological theory and that no serious ontological account could claim that
the world itself is indeterministic. But this is altogether another issue from
what Vollmer has raised in her critique of my views on atomic orbitals.

Let me conclude very briefly by saying that philosophers of chemistry
are interested in trying to break new ground on questions of ontology and
reduction, particularly as they arise in chemistry. Unfortunately the errors
in Vollmer’s book review and her failure to appreciate the subtlety in the
ideas discussed are likely to obscure these promising new developments. I
can only hope that philosophers of science will take a close look at this
book and see for themselves the wealth of ideas that are emerging from
this new field.

REFERENCES.

Paneth, F. A., 1962, “The Epistemological Status of the Concept of Element,” translated by
H. R. Post, British Journal for the Philosophy of Science 13: 1–14, 144–160.



 398

Scerri, Eric R. (2000), “Naive Realism, Reduction and the ‘Intermediate Position’”, in Nalini
Bhushan and Stuart Rosenfeld (eds.), Of Minds and Molecules: New Philosophical Per-
spectives on Chemistry. New York: Oxford University Press.

——— (2001), “The Recently Claimed Observation of Atomic Orbitals and Some Related
Philosophical Issues”, Philosophy of Science 67 (Proceedings): S76-S88.

Vollmer, S. H. (2003), “The Philosophy of Chemistry Reformulating Itself: Nalni Bhushan
and Stuart Rosenfeld’s Of Minds and Molecules: New Philosophical Perspectives on
Chemistry”, Philosophy of Science 70:383-390.