Full Idea
To say that x falls under f - or that x is an f - is to say what x is (in the sense Aristotle isolated).
Gist of Idea
In Aristotle's sense, saying x falls under f is to say what x is
Source
David Wiggins (Sameness and Substance [1980], 2.1)
Book Reference
Wiggins,David: 'Sameness and Substance' [Blackwell 1980], p.48
A Reaction
This is a key claim in Wiggins's main principle. I'm not convinced. He wants one main sortal to do all the work. I don't think Aristotle at all intended the 'nature' of an individual thing to be given by a single sortal under which it falls.