  Aristotle describes mind (nous, often also rendered as “intellect” or “reason”) as “the part of the soul by which it knows and understands” (De Anima iii 4, 429a9–10; cf. iii 3, 428a5; iii 9, 432b26; iii 12, 434b3), thus characterizing it in broadly functional terms. It is plain that humans can know and understand things; indeed, Aristotle supposes that it is our very nature to desire knowledge and understanding (Metaphysics i 1, 980a21; De Anima ii 3, 414b18; iii 3, 429a6–8). In this way, just as the having of sensory faculties is essential to being an animal, so the having of a mind is essential to being a human. Human minds do more than understand, however. It is equally essential to the human being to plan and deliberate, to ponder alternatives and strategize, and generally to chart courses of action. Aristotle ascribes these activities no less than understanding and contemplation to mind and consequently distinguishes the “practical mind” (or “practical intellect” or “practical reason”) from “theoretical mind” (or “theoretical intellect” or “theoretical reason”) ( Nicomachean Ethics vi 8 1143a35-b5; see  Aristotle: ethics).  In all these ways, investigating this capacity of soul thus has a special significance for Aristotle: in investigating mind, he is investigating what makes humans human.