This dissertation provides a new framework for thinking about the relationship of rationality to nature. The philosophy of F. W. J. Schelling, namely the philosophy of nature he develops between the years of 1797 and 1800, is a developmental account of nature and rationality. According to this account, the structures of rationality are independently manifested in the natural world, particularly in the activity of organisms. Thus by looking at the precursors to rationality in animals and their capabilities, we can develop a conception of rationality according to which it emerges in harmony with nature.  The developments in science and philosophy since 1800 require that Schelling's framework be supplemented and modified. And so I take Schelling's Naturphilosophie as inspiration and guide in developing accounts of rationality and nature in light of such developments.  The first three chapters of this dissertation are historical, focusing on the work of Kant and Schelling. In the first chapter I lay out Kant's conception of animal cognition, and in the second I explore the place he gives animals in nature, as it is cognized by rational subjects. I contend that Kant has trouble accounting for the complexity of animal cognition and behavior as well as the gradual emergence of reason. In the third chapter, I lay out Schelling's Naturphilosophie and the resultant conception of rationality, which does not suffer from the same problems.  In the fourth and fifth chapters, I discuss the work of philosophers such as John McDowell, Christine Korsgaard, Tyler Burge, and Michael Thompson. With varying degrees of success, these philosophers attempt to incorporate animals into their philosophical systems. And finally, in the sixth and seventh chapters, I lay out accounts of nature and rationality inspired by Schelling and mindful of evolutionary biology and the philosophical tradition discussed in the fourth and fifth chapters. I contend that treating nature and organic activity as purposive allows for a rich account of rationality as making explicit the norms implicit in this purposive activity.