'First reminding you that I am not the bag which contains the arguments, but that I extract them from Theaetetus, shall I tell you what amazes me in your friend Protagoras?' 'What may that be?' 'I like his doctrine that what appears is; but I wonder that he did not begin his great work on Truth with a declaration that a pig, or a dog-faced baboon, or any other monster which has sensation, is a measure of all things; then, while we were reverencing him as a god, he might have produced a magnificent effect by expounding to us that he was no wiser than a tadpole. For if sensations are always true, and one man's discernment is as good as another's, and every man is his own judge, and everything that he judges is right and true, then what need of Protagoras to be our instructor at a high figure; and why should we be less knowing than he is, or have to go to him, if every man is the measure of all things? My own art of midwifery, and all dialectic, is an enormous folly, if Protagoras' "Truth" be indeed truth, and the philosopher is not merely amusing himself by giving oracles out of his book.' Theodorus thinks that Socrates is unjust to his master, Protagoras; but he is too old and stiff to try a fall with him, and therefore refers him to Theaetetus, who is already driven out of his former opinion by the arguments of Socrates. Socrates then takes up the defence of Protagoras, who is supposed to reply in his own person--'Good people, you sit and declaim about the gods, of whose existence or non-existence I have nothing to say, or you discourse about man being reduced to the level of the brutes; but what proof have you of your statements? And yet surely you and Theodorus had better reflect whether probability is a safe guide. Theodorus would be a bad geometrician if he had nothing better to offer.'...Theaetetus is affected by the appeal to geometry, and Socrates is induced by him to put the question in a new form. He proceeds as follows:--'Should we say that we know what we see and hear,--e.g. the sound of words or the sight of letters in a foreign tongue?' 'We should say that the figures of the letters, and the pitch of the voice in uttering them, were known to us, but not the meaning of them.' 'Excellent; I want you to grow, and therefore I will leave that answer and ask another question: Is not seeing perceiving?' 'Very true.' 'And he who sees knows?' 'Yes.' 'And he who remembers, remembers that which he sees and knows?' 'Very true.' 'But if he closes his eyes, does he not remember?' 'He does.' 'Then he may remember and not see; and if seeing is knowing, he may remember and not know. Is not this a "reductio ad absurdum" of the hypothesis that knowledge is sensible perception? Yet perhaps we are crowing too soon; and if Protagoras, "the father of the myth," had been alive, the result might have been very different. But he is dead, and Theodorus, whom he left guardian of his "orphan," has not been very zealous in defending him.'