Abstract
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 notion of inseparability known from his critique of Plato's theory of ideas, he uses assumptions that are peculiar to his own theories. However, Aristotle uses a different notion of inseparability, he lays out as a criterion for a proper refutation 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 interpretative framework that does not impose his own theories unto other philosophers.