Full Idea
Things are said to be substance [ousia] because, far from being predicated of some subject, other things are predicated of them; in another way, for an intrinsic thing, it is the cause of being for it, as the soul is for the animal
Gist of Idea
Substance [ousia] is the subject of predication and cause [aitia?] of something's existence
Source
Aristotle (Metaphysics [c.324 BCE], 1017a13-23)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.126
A Reaction
This passage is used by M. Woods and others to argue that Aristotle has two different meanings for 'ousia' [substance, being]. Vasilis Politis argues against this view (pp.228). Aristotle is probably making two observations about a single thing.