[Objectivism agrees with Aristotle's formulation of the Law of Non-Contradiction]: These truths hold good for everything that is, and not for some special genus apart from others. And all men use them, because they are true of being qua being . . . . For a principle which everyone must have who understands anything that is, is not a hypothesis . . . . Evidently then such a principle is the most certain of all; which principle this is, let us proceed to say. It is, that the same attribute cannot at the same time belong and not belong to the same subject and in the same respect.