Page - 139 - in The Priority of Locomotion in Aristotle’s Physics

cal dependency.70 From what we have seen it is clear that there being x is a necessary condition for there to be y, while there being y is a sufficient con- dition for there to be x. Accordingly, we can say that whenever there is y, there also needs to be x. To give an example, one might say that the rain clouds over Berlin are prior in this way to it raining in Berlin: if it rains in Berlin, this necessarily implies that there are rain clouds over Berlin, yet, the mere fact of rain clouds over Berlin does not imply that it is raining in Berlin. A definition of ontological priority then may be the following: ONTOLOGICAL PRIORITY: x is ontologically prior to y, iff if there is y there also must be x, but not vice versa.71 The third argument that Aristotle presents for the priority claim aims at showing that locomotion is ontologically prior to any of the other kinds of change. According to our definition this means that if there is change in quality, quantity, or substance, then there must also be change in place, while it is not true that if there is change in place, there must also be some occurrence of any of the other kinds of change. Accordingly, the argument needs to show that if there is no locomotion, then there also cannot be any other kind of change, but not vice versa. Yet, if this is really what needs to be shown, one may wonder if this task has not been fulfilled already, since this is exactly what the first two arguments showed. One of the tasks of the remainder of this chapter will therefore be to find out in what special way this argument shows that locomotion has ontological priority over each of the other kinds of change and in what sense this is of importance for the larger project of showing that the change which is directly caused by the first unmoved mover can only be circular locomotion. 5.4.2 A third sense in which locomotion is ontologically prior While it has been made clear in the previous discussion that indeed only locomotion can be one, continuous and eternal, it still remains to explain in what way this implies that “locomotion must be primary.”72 For this is the conclusion that Aristotle obviously draws from what was said before, although it is really puzzling how one could actually arrive at this conclu- 70 See section 3.6, esp. p.68, n.79. There I also pointed out that what I call ontological dependency corresponds to the second kind of priority presented in Cat. 12 and to what Aris- totle would call priority in nature and in being in Met. V 11, 1019a1–4. 71 Or, if one would like to give a more formal definition of this relation: Po(x,y) ≡ j(y) → j(x) ⋀¬ ( j(x) → j(y)) 72 ἀνάγκη τὴν φορὰν εἶναι πρώτην, Phys. VIII 7, 260b25–26. Locomotion has ontological priority 139 ISBN Print: 9783525253069 — ISBN E-Book: 9783647253060 © 2014, Vandenhoeck & Ruprecht GmbH & Co. KG, Göttingen