Abstract

I IntroductionAt Metaphysics Γ 3, Aristotle argues that it belongs to a single discipline, which he calls first philosophy, to investigate both substance and a special class of claims which includes among its members the principle of non-contradiction. At Γ 4, after insisting that the PNC is, strictly speaking, indemonstrable, he sets forth a series of sketches of refutative arguments intended to show how it can, nonetheless, be substantiated. Traditionally, his main refutative argument has been taken to be embedded in the passage which runs from 1006a31 to b34. In that passage, he tries to show that anyone who denies the PNC and who can then be led, by means of an artfully arranged series of questions, to agree to a few seemingly modest theses about the signification of expressions of a certain type — which Aristotle illustrates with the general term ‘man’ — is thereby logically committed to the following modal claim: ‘It is necessary, then, if it is true to say that something is a man, that it be a bipedal animal'.