Eidos

The root of seeing

Eidos (εἶδος), with its twin idea, is the word Plato chose for the Forms. Both come from an ancient root meaning 'to see' — the same root behind Greek idein ('to see') and oida ('I know', literally 'I have seen'), Latin videre, and English 'vision', 'wit', and 'idea'. An eidos is, at root, 'the look' of a thing: its visible shape or aspect.

The look beheld by the mind

Plato took this everyday word for 'shape' or 'kind' and lifted it to name the intelligible realities, the eternal Forms. The paradox is deliberate and beautiful: the eidos is the true 'look' of a thing, yet it is invisible to the eyes and seen only by the mind. The Form of Beauty is what beauty really looks like — grasped in thought, never with the senses.

Form against matter

Aristotle kept the word but brought it down to earth, using eidos for the form that, together with matter, composes every physical thing — the shape and organizing principle that makes a lump of bronze a statue, or living flesh a human being. In this sense form is the essence and the actuality of a thing. From eidos comes, through Latin, our 'species', and the '-oid' of words like 'spheroid'.