Soul (psyché / anima) — The vital, organizing principle that, in the philosophical tradition, accounts for what distinguishes the living being from the inanimate and, more narrowly, for the intellectual and moral life of the human being. The Greek term psyché originally designated the breath that leaves the body at death; the Latin anima preserves the same root tied to air and breathing. For Plato, especially in the Phaedo and the Phaedrus, the soul is immortal, pre-exists the body, and survives it: temporarily imprisoned in matter, it longs to return to the world of intelligible Forms, the source of its knowledge. Aristotle, in the treatise On the Soul (De Anima), rejects this dualism and defines the soul as the form or first actuality of a natural body that has life in potentiality: it is not a separable substance but the principle that organizes and actualizes the vital functions — nutritive, sensitive, and rational. In Modernity, Descartes reframes the question in terms of two substances: the soul as res cogitans (thinking substance), distinct from and independent of the body understood as res extensa (extended substance), inaugurating the mind-body problem that still occupies philosophy today. The central opposition thus runs along two axes: soul as separate substance (Plato, Descartes) versus soul as a principle immanent in the body (Aristotle); and soul as the seat of thought versus soul as the mere principle of life. Closely related concepts are dualism — the thesis that mind and body are distinct realities — and immortality, heir to the Platonic conception.
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