Descartes' System of Natural Philosophy (review)

Stephen Gaukroger, author of a definitive biography of Descartes, has now written an excellent account of Descartes's natural philosophy as presented in his Principia philosophiae. Gaukroger claims that the roots of modernity lay in the philosophies of Francis Bacon and René Descartes, both of whom regarded natural philosophy, rather than either moral philosophy or metaphysics, as the core of the philosophical enterprise. Whereas Bacon developed his ideas from a background steeped in the writings of the Renaissance humanists who emphasized moral philosophy, Descartes developed his ideas in the context of Scholastic philosophy, particularly the textbooks of the Jesuits that he had encountered at La Flèche and that located the foundations of philosophy in metaphysics.

Regarding the unpublished early works, Le monde and L'homme, as suppressed parts of Descartes's mature project and taking seriously Descartes's stated intention of dealing with living things and humans along with the physical world in his natural philosophy, Gaukroger presents a detailed account of this "complete" version of the Principia philosophiae. In a series of six chapters, he explicates Descartes's views on the principles of knowledge, the principles of material objects, the visible universe, the Earth, living things, and man. In addition to Le monde and L'homme, Gaukroger draws on Les Passions de l'âme as an important source for Descartes's views on human nature.

Gaukroger situates Descartes's natural philosophy in the context of the Scholastic textbook tradition in a chapter preceding his account of the Principa philosophiae. He delves into the history of medieval universities, the place of natural philosophy in the medieval curriculum, and the changing relationship between metaphysics and natural philosophy, particularly after the Condemnations of 1277. Difficulties in reconciling Aristotelian natural philosophy and Christian theology, which had been formulated in terms of Aristotelian metaphysics, continued into the sixteenth century and provided the immediate background to the Jesuit commentaries and textbooks to which Descartes was exposed as a student. In these works, Jesuit philosophers attempted to derive a coherently unified Christian Aristotelianism from first principles. Gaukroger reminds us that Descartes's Principia philosophiae was a deliberate attempt to replace these Jesuit textbooks with one based on mechanistic principles.

Despite the strength of Gaukroger's book as a contextualized study of a major philosophical figure who is frequently treated in an entirely ahistorical way, the book is not without its problems. The main problem is one that plagues many studies of Descartes (and other canonical figures in the history of philosophy), to wit, the presumption that he is somehow unique. For example, Gaukroger writes at length about Descartes's views about the differences between animals and humans with regard to cognition, arguing that Descartes did not consider animals to be automata because they lack rational souls but rather that they actually experience some but not all of the more abstract or reflexive forms of cognition usually ascribed to humans. Gaukroger does not mention the fact that many other early modern philosophers held a view like this. For example, Descartes's contemporary and fellow mechanical philosopher Pierre Gassendi claimed that animals could know universals, as when a dog recognizes that it is a human that is approaching, but differ from humans in not being capable of contemplating the nature of universality per se. Descartes was part of a community of thinkers concerned with similar problems, and his natural philosophy can be illuminated by viewing him in that context as well as against the backdrop of Scholasticism.

Gaukroger underplays the significance of theology for Descartes's philosophy. Although he discusses how God's attributes, especially immutability, provide the basis for Descartes's laws of motion, he does not explore the specific aspects of Descartes's theological presuppositions and the way they influenced his entire natural philosophical project. Gaukroger repeats the received view that "One of the principal tasks of a mechanistic natural philosophy...