Page - 194 - in The Priority of Locomotion in Aristotle’s Physics

(3) Therefore, a fortiori locomotion does not change the essence of its subject. (1, 2) Premise (1) takes up what is said in sentence (2) of our passage, namely that changes in quality and quantity change their respective subject in being while locomotion does not. Premise (2) refers to the fact that both of the kinds that can change their subject’s being, because they are non-substantial changes, cannot change its essence. The conclusion then seems correct. But this argument involves an implicit premise that needs to be made explicit: only a change that can change its subject in being can change its subject’s essence. This is due to the fact that, as I stated above, every change in essence is a change in being, while not every change in being is necessarily also a change in essence. If change in quantity and quality, which are changes in being, are incapable of making their subject depart from its essence, how then could locomotion be capable of doing so? In other words, if locomotion does not have the power to change x in being, this is even more true of its power to change x in essence. The argument then is correct. However, it does not explain why locomo- tion should be less responsible, or even the least responsible, for its subject’s departing from its essence (ἥκιστα τῆς οὐσίας ἐξίσταται) than alteration, growth and diminution. Again, these are all non-substantial changes, and thus all of them are incapable of changing their subject’s essence the same way; none of them does so more or less than any of the others. But it is this very attribute of changing its subject’s essence the least which is supposed to make locomotion prior in essence to the other kinds of change. Therefore, one should try to find a way in which it is appropriate to speak of such a difference in degree. In what follows I will argue that, in a certain respect, it is possible that the other two kinds of change are more responsible for their subject’s change in essence than locomotion. By relat- ing what I have said so far to a significant passage from Aristotle’s discus- sion of alteration in Phys. VII 3, my first step will be to suggest that altera- tion and change in quantity, in contrast to locomotion, seem to involve their subject’s departing from its essence, as both may serve as necessary parts of certain substantial changes (7.2.4). But since this proposal, as we will see, turns out to be problematic in many respects, my second step will be to argue that the true reason for the claimed difference between locomo- tion and the other kinds of non-substantial change is that the latter in prin- ciple may, but do not have to, result in a change in essence of their subject, and that locomotion in this sense is indeed special (7.2.5). 194 Locomotion is prior in essence ISBN Print: 9783525253069 — ISBN E-Book: 9783647253060 © 2014, Vandenhoeck & Ruprecht GmbH & Co. KG, Göttingen