Full Idea
There can be no doubt that matter is a substance. Consider all changes between opposites. In all of them there is something that underlies the change.
Gist of Idea
Substance must exist, because something must endure during change between opposites
Source
Aristotle (Metaphysics [c.324 BCE], 1042a30)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.234