Plato: The Republic

5. BOOK V (continued)

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 corresponded to being and ignorance of necessity to not-being, for that intermediate between being and not-being there has to be discovered a corresponding intermediate between ignorance and knowledge, if there be such?

Certainly.

Do we admit the existence of opinion?

Undoubtedly.

As being the same with knowledge, or another faculty?

Another faculty.

Then opinion and knowledge have to do with different kinds of matter corresponding to this difference of faculties?

Yes.

And knowledge is relative to being and knows being. But before I proceed further I will make a division.

What division?

I will begin by placing faculties in a class by themselves: they are powers in us, and in all other things, by which we do as we do. Sight and hearing, for example, I should call faculties. Have I clearly explained the class which I mean?

Yes, I quite understand.

Then let me tell you my view about them. I do not see them, and therefore the distinctions of fire, colour, and the like, which enable me to discern the differences of some things, do not apply to them. In speaking of a faculty I think only of its sphere and its result; and that which has the same sphere and the same result I call the same faculty, but that which has another sphere and another result I call different. Would that be your way of speaking?