  On such an account, Aristotle is showing the opponent that if she wants to reject PNC she must pick out the same object and say that contradictory predicates apply, but if she does not mean anything definite by “human being”, for example, then she will be unable to pick out a subject of predication, for example, a human being, and say that contradictory predicates apply. Saying that an individual human being is a human being and not a human being, where the first means “two-footed animal” and the latter means something different is not to reject PNC. That is why the opponent must pick a particular word with a definite meaning.