Full Idea
In some instances the account of the what-it-was-to-be-that-thing contains the parts of the thing defined and in others not.
Gist of Idea
Sometimes parts must be mentioned in definitions of essence, and sometimes not
Source
Aristotle (Metaphysics [c.324 BCE], 1037a22)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.209
A Reaction
This is helpful in understanding what an essence is supposed to be. I take it to be sometimes a structure, with parts, and sometimes more like a guiding principle, more abstract in character.