Full Idea
Particular perceptible substances are excluded from definition. ...An object that admits of being in a variety of states is an object of opinion, and thus incontrovertibly not of definition.
Gist of Idea
Particulars are not definable, because they fluctuate
Source
Aristotle (Metaphysics [c.324 BCE], 1039b30)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.223
A Reaction
This more or less demolishes my original reading of Aristotle, so back to the drawing board. We need to revise Aristotle. He says differentiae home in the individual but never get there. I (now) say cross-referencing of universals gets you there.