Ousia (οὐσία) — “Substance,” “being,” “essence.” Difficult to translate: literally “what is” — the being-there of something. For Aristotle, ousia designates (a) the concrete individual (Socrates, this horse) — primary substance; (b) the species or genus (human, animal) — secondary substance. The question of ousia runs through all of Western metaphysics: what exists in a primary and independent manner?
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