On the Soul (Greek: Περὶ Ψυχῆς, Peri Psychēs; Latin: De Anima) is a major treatise written by Aristotle c. 350 BC. His discussion centres on the kinds of souls possessed by different kinds of living things, distinguished by their different operations. Thus plants have the capacity for nourishment and reproduction, the minimum that must be possessed by any kind of living organism. Lower animals have, in addition, the powers of sense-perception and self-motion (action). Humans have all these as well as intellect.
Aristotle holds that the soul (psyche, ψυχή) is the form, or essence of any living thing; it is not a distinct substance from the body that it is in. It is the possession of a soul (of a specific kind) that makes an organism an organism at all, and thus the notion of a body without a soul, or of a soul in the wrong kind of body, is simply unintelligible. (He argues that some parts of the soul — the intellect — can exist without the body, but most cannot.)
