Full Idea
Perception is always of something that is, and it is infallible, which suggests that it is knowledge.
Gist of Idea
Perception is infallible, suggesting that it is knowledge
Source
Plato (Theaetetus [c.364 BCE], 152c)
Book Reference
Plato: 'Theaetetus', ed/tr. Waterfield,Robin [Penguin 1987], p.31