Full Idea
The substance of each thing ...is the primary cause of being for it.
Gist of Idea
A thing's substance is its primary cause of being
Source
Aristotle (Metaphysics [c.324 BCE], 1041b27)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.229
A Reaction
Wedin says that here Aristotle announces this 'with finality'. This is 'for each thing', and hence is essence at the level of the individual, not of the kind. Identifying the 'cause of being' of a thing is taken to be its best possible explanation.