Full Idea
These two ideas, greatness and smallness, exist, do they not? For if they did not exist, they could not be opposites of one another, and could not come into being in things.
Gist of Idea
Greatness and smallness must exist, to be opposed to one another, and come into being in things
Source
Plato (Parmenides [c.366 BCE], 149e)
Book Reference
Plato: 'Plato IV (Cratylus,Parmenides,Hippias Maj, Min)', ed/tr. Fowler,H.N. [Harvard Loeb 1926], p.277