Full Idea
Real enquiries stand revealed as causal enquiries (and the cause is the what-it-was-to-be-that-thing [to ti en einai]).
Gist of Idea
Real enquiries seek causes, and causes are essences
Source
Aristotle (Metaphysics [c.324 BCE], 1041a28)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.228
A Reaction
As good a quotation as any for showing that Aristotelian essences exist entirely by their role in explanation.