Full Idea
Parmenides and Melissus were the first to appreciate that there must be unchanging entities, if recognition and knowledge are to exist.
Gist of Idea
Something must be unchanging to make recognition and knowledge possible
Source
comment on Parmenides (fragments/reports [c.474 BCE], A25) by Aristotle - On the Heavens 298b14
Book Reference
'The First Philosophers', ed/tr. Waterfield,Robin [OUP 2000], p.61