Johannes Fritsche

It has been discussed whether in his two definitions of nature in Physics II, Aristotle means a mover, a passive principle or both kinds of principles. I argue that he means a mover. I discuss several occurrences of the expression archê kinêseôs (›principle of motion‹) in particular in Aristotle’s Metaphysics IX and Physics (especially 255 b 29–31). Aristotle means most often a mover, sometimes »the time/site of the beginning of the motion« and never a passive principle. Finally, I briefly discuss the status and function of the two definitions of nature within the context of Physics II and the entire Physics.

Most often, it has been maintained that Aristotle’s refutation of the thesis that space is matter or form is dialectically invalid. For, employing the notionof inseparability known from his critique of Plato’s theory of ideas, he uses assumptions that are peculiar to his own theories. However, Aristotle uses adifferent notion of inseparability (a part is »inseparable« from a whole if the latter cannot exist without the former), he lays out as a criterion for a properrefutation of the thesis in question precisely that it must not employ assumptions that are not shared by his opponents, and his refutation lives up to this standard.Lines 209 b 6–17 and 209 b 17–32 show that a major aspect of his development of his basic concepts in the Physics is precisely his effort to gain an interpretativeframework that does not impose his own theories unto other philosophers.

Aristotle’s interpretation of χẃρα (= matter and space) has most often been regarded as an excellent example of his supposed inability to read otherphilosophers other than through the lenses of his own technical vocabulary and its implications. However, his reasoning is independent of his own take on theissue of prime matter, his claim is right, and it amounts to the thesis that χẃρα is neither matter nor space. It is shown how 209 b 6–17 is located within the largercontext of the Physics and its agenda concerning the issue of principles and causes of natural beings.