Page - 193 - in The Priority of Locomotion in Aristotle’s Physics

cept of essence does not play any role in the second argument: locomotion is prior not because it changes its subject in essence (in the strict sense) least, but because it does not change its being (in the Wagnerian sense) at all. For a change in being to occur, however, it does not matter whether the change’s subject undergoes a change in essence or not. According to this understanding, the concept of essence would play no role at all in deciding whether x has priority in essence over y. Thus the definition of priority in essence underlying the second argument would be different from the one presupposed by the first argument for locomotion’s priority in essence. If this were the case and Wagner’s reading correct, then Aristotle is not pre- senting two arguments for one and the same way in which locomotion has priority, namely with respect to essence (κατ᾽ οὐσίαν), but is rather arguing for two different ways in which it does, and is falsely using the same name for both, thus making the mistake of equivocation. But if, as I see it, Aristotle thinks that both arguments show that locomo- tion is prior in the same way, then the definition of priority in essence that underlies the first argument also needs to be presupposed for the second one. Another reason that speaks for taking the phrase ‘to depart from its essence’ as referring to a substantial change, is that when Aristotle employs this term elsewhere, it stands for a change in the essence of the change’s subject, which suggests that this is also the case here.60 But if my assumption is correct and the process of x undergoing a change in being really differs from x departing from its essence, one still has to face the problem which I mentioned above. If the fact that a change in quality or quantity, in contrast to locomotion, changes its subject x’s being (sentence 2) accounts for its changing x’s essence more than locomotion, but less than generation and corruption (sentence 1), then it seems that these non-sub- stantial kinds of change must be taken to somehow lead to or involve a change in x’s essence, that is, a substantial change, whereas locomotion does not. One might think that a way to deal with this problem is to read the argument as an a fortiori argument which could be reconstructed as fol- lows: (1) Of the non-substantial changes, only change in quantity and change in quality change the being of their subjects. (2) Neither change in quantity, nor change in quality changes the essence of its subject. 60 This phrase does not seem to be used very often in Aristotle. Apart from the passage in Physics VIII, there is one in de An. I 3 (see 406b11–15). Also in Top. VI 6 (see 145a3–12) a form of ἐξίστημι in combination with τῆς οὐσίας is used in order to signify a change in sub- stance. Locomotion alone preserves its subject’s essence 193 ISBN Print: 9783525253069 — ISBN E-Book: 9783647253060 © 2014, Vandenhoeck & Ruprecht GmbH & Co. KG, Göttingen