SOCRATES: Why, my dear boy, you are young, and therefore your ear is quickly caught and your mind influenced by popular arguments. Protagoras, or some one speaking on his behalf, will doubtless say in reply,--Good people, young and old, you meet and harangue, and bring in the gods, whose existence or non-existence I banish from writing and speech, or you talk about the reason of man being degraded to the level of the brutes, which is a telling argument with the multitude, but not one word of proof or demonstration do you offer. All is probability with you, and yet surely you and Theodorus had better reflect whether you are disposed to admit of probability and figures of speech in matters of such importance. He or any other mathematician who argued from probabilities and likelihoods in geometry, would not be worth an ace. THEAETETUS: But neither you nor we, Socrates, would be satisfied with such arguments. SOCRATES: Then you and Theodorus mean to say that we must look at the matter in some other way? THEAETETUS: Yes, in quite another way. SOCRATES: And the way will be to ask whether perception is or is not the same as knowledge; for this was the real point of our argument, and with a view to this we raised (did we not?) those many strange questions. THEAETETUS: Certainly. SOCRATES: Shall we say that we know every thing which we see and hear? for example, shall we say that not having learned, we do not hear the language of foreigners when they speak to us? or shall we say that we not only hear, but know what they are saying? Or again, if we see letters which we do not understand, shall we say that we do not see them? or shall we aver that, seeing them, we must know them? THEAETETUS: We shall say, Socrates, that we know what we actually see and hear of them--that is to say, we see and know the figure and colour of the letters, and we hear and know the elevation or depression of the sound of them; but we do not perceive by sight and hearing, or know, that which grammarians and interpreters teach about them. SOCRATES: Capital, Theaetetus; and about this there shall be no dispute, because I want you to grow; but there is another difficulty coming, which you will also have to repulse. THEAETETUS: What is it? SOCRATES: Some one will say, Can a man who has ever known anything, and still has and preserves a memory of that which he knows, not know that which he remembers at the time when he remembers? I have, I fear, a tedious way of putting a simple question, which is only, whether a man who has learned, and remembers, can fail to know? THEAETETUS: Impossible, Socrates; the supposition is monstrous. SOCRATES: Am I talking nonsense, then? Think: is not seeing perceiving, and is not sight perception? THEAETETUS: True. SOCRATES: And if our recent definition holds, every man knows that which he has seen? THEAETETUS: Yes. SOCRATES: And you would admit that there is such a thing as memory? THEAETETUS: Yes.