Full Idea
Every substance seems to signify a certain 'this'. As regards the primary substances, it is indisputably true that each of them signifies a certain 'this'; for the thing revealed is individual and numerically one.
Gist of Idea
A primary substance reveals a 'this', which is an individual unit
Source
Aristotle (Categories [c.331 BCE], 03b10)
Book Reference
Aristotle: 'Categories and De Interpretatione', ed/tr. Ackrill,J.R. [OUP 1963], p.9
A Reaction
The notion of 'primary' substance is confined to this earlier metaphysics of Aristotle.