Page - 191 - in The Priority of Locomotion in Aristotle’s Physics

change its subject’s essence at all. But if, of two changes x and y, x does not change its subject at all while y does in some way, it is true to say that x changes its subject less than y—even if x does not change its subject in any way whatsoever. A substantial change, however, is defined as a change either from what is to what is not, or from what is not to what is.56 Hence, a substantial change, in contrast to a non-substantial one, is not a change between contraries, but between contradictories, which means that there are no intermediates between the starting point and endpoint of the change.57 Accordingly, a change in essence cannot be a matter of degree: a (complete) change in essence, by definition, cannot change its subject’s essence more or less than any other (complete) change in essence. Sentence (1), however, suggests that there are degrees to which a change’s subject may depart from its essence, i.e. undergo a change with respect to its essence. As I have shown, there is no problem in saying that any substantial change changes x’s essence more or to a higher degree than any of the non-substantial ones. But there is a problem in saying that, of the four kinds of change, locomo- tion changes its subject’s essence least. For this requires that locomotion not only change its subject’s essence less than coming to be and corruption, but also less than change in quality and in quantity. For this to be true it would suffice to show either that (1) locomotion does not change its sub- ject’s essence at all, while change in quality and quantity do in some way, or that (2) locomotion also does so, though to a lower degree than change in quantity and quality. This presupposes two problematic assumptions. First, it would imply that there are different degrees to which something may change in essence, which, as I just stated, contradicts what Aristotle says elsewhere about change in essence, i.e. in substance. Second, this implies that, at the very least, change in quantity or quality—and possibly even in locomotion—may change its subject’s essence. Let us start with the second of the two assumptions. As I said before, it would clearly collide with basic theorems of Aristotle’s theory of change. If my face turns hot and red, or if I become larger due to laziness, does this imply a departure from—that is a change in—my essence, while no such change occurs when I walk from my office to the kitchen? In all three cases, accidental properties, at best, are changed, and thus none of them affects the essence of its respective subject—which is in accordance with the fact that Aristotle explicitly distinguishes change in quality, quantity and place, understood as non-substantial changes, from coming to be and corruption: the former are defined as changing something of a substance, but not the 56 Phys. V 1, 224b8–10 and 225a12–20. 57 See for instance Phys. V 1, 225a34–b5. Locomotion alone preserves its subject’s essence 191 ISBN Print: 9783525253069 — ISBN E-Book: 9783647253060 © 2014, Vandenhoeck & Ruprecht GmbH & Co. KG, Göttingen