The Republic by Plato Part 5 Page 96

(You must answer for him.)

I answer that he knows something.

Something that is or is not?

Something that is; for how can that which is not ever be known?

And are we assured, after looking at the matter from many points of view, that absolute being is or may be absolutely known, but that the utterly non-existent is utterly unknown?

Nothing can be more certain.

Good. But if there be anything which is of such a nature as to be and not to be, that will have a place intermediate between pure being and the absolute negation of being?

Yes, between them.

And, as knowledge