S. Marc Cohen

Aristotle takes up the topic of change (or coming-to-be and ceasing-to-be) in both the Physics and De Generatione et Corruptione. He distinguishes between simple coming-to-be (substantial change), as when something comes into existence, and qualified coming-to-be (accidental change), as when an already existing thing alters, or moves, or changes in some other way. But he also maintains a persistence principle: that in every change, whether simple or qualified, there is something that persists throughout the change. I examine the question of whether this principle threatens the viability of the distinction between substantial and accidental change by comparing what Aristotle has to say about it in the Physics with what he says in GC. In the process, I discuss several recent treatments of the topic as well as some conflicting views about the role, if any, of prime matter in Aristotle's account of substantial change.

Aristotle's claim in Metaphysics Z.6 that "each substance is the same as its essence" has long puzzled commentators. For it seems to conflict with two other Aristotelian theses: (1) primary substances are individuals (e.g., Socrates and Callias), and (2) essences are universals (e.g., Man and Horse). Three traditional solutions to this difficulty are considered and rejected. Instead, to make the Z.6 equation consistent with (1) and (2), I propose that it be interpreted to be making something other than a straightforward identity claim. Callias is the same as his essence in the sense that to be identical to Callias is to be the same man as Callias (where Man is the essence of Callias). In general, x is identical to y if, and only if, x and y are the same E (where E specifies the "what it is to be" for x, i.e., the essence of x). So each of Socrates and Callias is the same as his essence, and Man is that essence, but Socrates and Callias are not identical, for they are not the same man.

It is traditionally maintained that according to Aristotle, matter provides a principle of individuation. Objections of several sorts have been raised against this interpretation. One objection holds that for Aristotle it is form, rather than matter, that individuates. A more radical objection is that Aristotle does not propose any principle of individuation at all. Any adequate discussion of this issue must make clear precisely what problems such a principle is meant to address. This in turn requires that several important distinctions be observed: (1) principles of individuation vs. principles of unity; (2) metaphysical vs. epistemological principles; (3) synchronic vs. diachronic unity and individuation; numerical vs. qualitative identity. After examining the objections in the light of these distinctions, I conclude that the objections cannot be sustained, and that, with appropriate qualifications, the traditional interpretation gives us the right idea about Aristotle.