ons are crucial to Aristotle's logic. Definitions are the hairline. They must cleanly separate items into chair and not-chair. Yet at the outset of De Anima, he admits the difficulty of finding any method of definition. It is a remarkable concession, for if we can't specify the hairline, classes blur at

ons are crucial to Aristotle's logic. Definitions are the hairline. They must cleanly separate items into chair and not-chair. Yet at the outset of De Anima, he admits the difficulty of finding any method of definition. It is a remarkable concession, for if we can't specify the hairline, classes blur at