Eidos (εἶδος) — a Greek word meaning “form,” “aspect,” or “visible figure,” derived from the verb idein (“to see”); it names what shows itself of a thing and, by philosophical extension, its intelligible structure or essence. In Plato, eidos (often interchangeable with idéa) designates the Ideas or Forms: eternal, immutable, universal realities, separate from the sensible world, which constitute the true object of knowledge. Particular objects are mere copies that imitate (mimesis) and participate in (methexis) these Forms — thus a concrete, perishable horse is what it is only by sharing in the single, perfect Form of Horse, grasped not by the senses but by the intellect. Aristotle shifts the concept: for him the eidos does not exist separately but is the immanent form of each thing, the principle that organizes matter (hyle) and makes it a determinate being. In his hylomorphic doctrine, set out above all in the Metaphysics, every sensible substance is a compound of form and matter — the soul, for example, is the eidos of the living body. In Husserl’s phenomenology the term resurfaces to name the essence grasped by eidetic intuition (Wesensschau), reached when, through imaginative variation, we abstract from an object’s contingent features until we apprehend what in it is necessary and invariant. The eidos is thus closely bound up with neighboring notions such as idéa, ousía (substance), and morphé (sensible shape).
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