Full Idea
We must have some previous knowledge of equality, before the time when we saw equal things, but realised that they fell short of it.
Gist of Idea
We must have a prior knowledge of equality, if we see 'equal' things and realise they fall short of it
Source
Plato (Phaedo [c.382 BCE], 075a)
Book Reference
Plato: 'The Last Days of Socrates', ed/tr. Tredennick,Hugh [Penguin 1969], p.124