Essence and potentiality: Aristotelian strategies of addressing problems of change and persistence
When Aristotle makes his case that time is a property of motion, he not only argues that time depends for its existence on motion, but that it derives its structural properties from motion as well. But if this is to avoid a vicious circularity, then motion cannot presuppose time, and the order of motion must be definable in abstraction from the order of time. I argue that Aristotle is able to do exactly this, based upon his theory of act and potency (energeia and dunamis), and upon the theory that all natural change is teleological. I propose that a linear order may be defined on the phases of a change, using the relation “x is potentially y,” where x and y range over different phases of an Aristotelian natural substance (e.g., Socrates-as-a-boy, Socrates-as-a-man, etc.). This is possible, I claim, because a special asymmetric potentiality is involved which marks out the stages of a change as prior and posterior based upon their proximity to a given goal, rather than upon their order in a temporal sequence. I also argue that if x and y appear in states of affairs that obtain at different times, then the “x is potentially y” relation provides a criterion for diachronic identity, since it relates a single entity at one time to itself at another time. Moreover, I argue, based on an account that takes forms to be individuals that persist over time, that the forms which give substances these special potentialities are early analogues of the individual essences proposed by the Stoics and by Duns Scotus as criteria for identity, and by contemporary metaphysicians such as Kaplan and Plantinga to secure identity across possible worlds. I look at two ancient puzzles about persistence, viz., the Growing Argument by Epicharmus, and a similar puzzle about alteration mentioned by Aristotle in Phys. 4.11, and assess the adequacy of Aristotle’s criterion of identity for solving them. As a point of comparison, I also assess the solution to the Growing Argument proposed by the Stoic philosopher Chrysippus, which features a reductio ad absurdum of certain premises of these puzzles.