Full Idea
Suppose we only ever saw bronze circles - would that make the bronze a formal part of the circle?
Gist of Idea
If we only saw bronze circles, would bronze be part of the concept of a circle?
Source
Aristotle (Metaphysics [c.324 BCE], 1036b01)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.207
A Reaction
This is Aristotle spotting the problem of coextensionality (the renate/cordate problem) 2300 years ago. Don't underestimate those Greeks.