Full Idea
That which is different is different from something under some aspect, so that there must be something the same in respect of which they differ.
Gist of Idea
For two things to differ in some respect, they must both possess that respect
Source
Aristotle (Metaphysics [c.324 BCE], 1054b26)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.295