Full Idea
There are two ways of being a substrate [to hupokeimenon], either as possessor of thisness (as the animal is a substrate for its properties) or as matter is a substrate for the actuality.
Gist of Idea
A substrate is either a 'this' supporting qualities, or 'matter' supporting actuality
Source
Aristotle (Metaphysics [c.324 BCE], 1038b05)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.216
A Reaction
A bit confusing, since the possessor of thisness will obviously have what we call 'identity', whereas matter cannot have identity on its own (because it also needs form).