SOCRATES: And is memory of something or of nothing? THEAETETUS: Of something, surely. SOCRATES: Of things learned and perceived, that is? THEAETETUS: Certainly. SOCRATES: Often a man remembers that which he has seen? THEAETETUS: True. SOCRATES: And if he closed his eyes, would he forget? THEAETETUS: Who, Socrates, would dare to say so? SOCRATES: But we must say so, if the previous argument is to be maintained. THEAETETUS: What do you mean? I am not quite sure that I understand you, though I have a strong suspicion that you are right. SOCRATES: As thus: he who sees knows, as we say, that which he sees; for perception and sight and knowledge are admitted to be the same. THEAETETUS: Certainly. SOCRATES: But he who saw, and has knowledge of that which he saw, remembers, when he closes his eyes, that which he no longer sees. THEAETETUS: True. SOCRATES: And seeing is knowing, and therefore not-seeing is not-knowing? THEAETETUS: Very true. SOCRATES: Then the inference is, that a man may have attained the knowledge of something, which he may remember and yet not know, because he does not see; and this has been affirmed by us to be a monstrous supposition. THEAETETUS: Most true. SOCRATES: Thus, then, the assertion that knowledge and perception are one, involves a manifest impossibility? THEAETETUS: Yes. SOCRATES: Then they must be distinguished? THEAETETUS: I suppose that they must. SOCRATES: Once more we shall have to begin, and ask 'What is knowledge?' and yet, Theaetetus, what are we going to do? THEAETETUS: About what? SOCRATES: Like a good-for-nothing cock, without having won the victory, we walk away from the argument and crow. THEAETETUS: How do you mean? SOCRATES: After the manner of disputers (Lys.; Phaedo; Republic), we were satisfied with mere verbal consistency, and were well pleased if in this way we could gain an advantage. Although professing not to be mere Eristics, but philosophers, I suspect that we have unconsciously fallen into the error of that ingenious class of persons. THEAETETUS: I do not as yet understand you. SOCRATES: Then I will try to explain myself: just now we asked the question, whether a man who had learned and remembered could fail to know, and we showed that a person who had seen might remember when he had his eyes shut and could not see, and then he would at the same time remember and not know. But this was an impossibility. And so the Protagorean fable came to nought, and yours also, who maintained that knowledge is the same as perception. THEAETETUS: True.