Full Idea
The what-it-was-to-be-that-thing [to ti en einai] for a single thing is what-it-was-to-be-that-thing for a particular.
Gist of Idea
The essence of a single thing is the essence of a particular
Source
Aristotle (Metaphysics [c.324 BCE], 1054a16)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.292
A Reaction
This seems to give clear support for the view I favour, that Aristotle believes in individual essences, and not just generic kinds.