187–188
Theaetetus
THEAET. Of course.
Socrates
SOC. How, then, shall we set about it? What is it that we do say? Do we say that in every case of opinion there is a false opinion, and one of us has a false, and another a true opinion, because, as we believe, it is in the nature of things that this should be so?
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Theaetetus
THEAET. Yes, we do.
Socrates
SOC. Then this, at any rate, is possible for us, is it not, regarding all things collectively and each thing separately, either to know or not to know them? For learning and forgetting, as intermediate stages, I leave out of account for the present, for just now they have no bearing upon our argument.
Theaetetus
THEAET. Certainly, Socrates, nothing is left in any particular case except knowing or not knowing it.
Socrates
SOC. Then he who forms opinion must form opinion either about what he knows or about what he does not know?
Theaetetus
THEAET. Necessarily.
Socrates
SOC. And it is surely impossible that one who knows a thing does not know it, or that one who does not know it knows it.
5
Theaetetus
THEAET. Certainly.
Socrates
SOC. Then does he who forms false opinions think that the things which he knows are not these things, but some others of the things he knows, and so, knowing both, is he ignorant of both?
Theaetetus
THEAET. That is impossible, Socrates.
Socrates
SOC. Well then, does he think that the things he does not know are other things which he does not know—which is as if a man who knows neither Theaetetus nor Socrates should conceive the idea that Socrates is Theaetetus or Theaetetus Socrates?
Theaetetus
THEAET. That is impossible.
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