Descartes on Forms and Mechanisms (review)

Recent research by scholars such as Dennis Des Chene and Roger Ariew, among others, has deepened our knowledge of the Scholastic context of Descartes's philosophy, especially his metaphysics and natural philosophy. Helen Hattab's book is a valuable addition to this literature. Her main concern is the development from explanations by Aristotelian substantial forms in late Scholastic thought to the allegedly more perspicuous explanations that characterized the new mechanistic science. More specifically, she investigates the various contexts of Descartes's rejection of substantial forms, looking behind the rhetoric of his attack to what she claims was in fact the theory he had in sight and the arguments he used against it. The result is a more complex story than is usually told and a fascinating portrait of the way in which Aristotelian natural philosophy evolved in later Scholasticism (especially Suárez) and in effect made possible its own demise.

In the first half of the book, Hattab offers a two-part narrative of the internal dynamics leading to the decline and fall of Aristotelian explanations in natural philosophy. She begins with an examination of Thomas Aquinas's account of substantial forms, primarily to compare it with that of Suárez. She argues that a number of innovations by Suárez made the Aristotelian account of forms unstable and thus susceptible to Cartesian critique. These include modeling all substantial forms (including corporeal substantial forms, presumably elicited from and dependent upon matter but still in some sense "substantial") on the paradigm of the human soul, thus allowing Descartes eventually to accuse the doctrine of incoherence; and isolating and highlighting the substantial form's role as efficient cause from its role as formal cause, thus turning these forms into something like "internal active soul-like entities which, by their mysterious agency, ensure that the accidents of the composite are restored and united to one another" (64). This, and not Aquinas's version, is the model of substantial forms that, she claims, Descartes targets in his critique and whose weaknesses allow that critique to be as effective as it was.

After clarifying the Suárezian conditions that made possible Descartes's successful negative case against substantial forms, Hattab turns to the way in which changes in Aristotelian natural philosophy, its mechanics in particular, supported the positive part of Descartes's campaign in which explanations via substantial forms are replaced by the principles of the mechanical philosophy. While some of the skeptical considerations offered by contemporary thinkers such as Francisco Sanchez are rendered more effective by the changes introduced by Suárez, others can be parried by Suárez's innovations; they thus leave substantial forms qua efficient causal principles untouched and no better or worse off than mechanistic modes of explanation. However, it is, again, a dynamic internal to Aristotelian philosophy that, paradoxically, hastens its demise—namely, its science of mechanics and the application of mathematics (geometry in particular) to physical phenomena by such figures as Giovanni di Guevara and Josephus Blancanus. "After elevating mechanics from an art to a mathematical science, Aristotelian commentators gradually undermined the centuries-old divisions between artificial machines and natural objects, and mathematical versus scientific demonstrations" (119). The way was now open for Descartes to make his move and inaugurate a true mathematical, non-Aristotelian physics.

The second half of the book is devoted to the development of Descartes's strategy for replacing Scholastic forms with mechanistic explanations. Hattab argues that, early on, Descartes was committed to "forms," but only understood in terms consistent with the mechanical philosophy. This conciliatory Descartes wanted to preserve material substantial forms at the level of physics, but reinterpreted in terms amenable to mathematization. His goal at this point, she suggests, was to persuade others, through a posteriori reasoning, that geometric-friendly explanations framed in terms of matter and motion were just as good and fruitful as (if not better than) Scholastic ones, but not to provide a deep metaphysical refutation of substantial forms. Such an a priori elimination of forms...