Theaetetus

​SOCRATES: Well, you seem to have given a by no means ordinary account of knowledge, but rather the very one that Protagoras also used to give. However, he has said these same things in a somewhat different way. For he says somewhere, “Man is the measure of all things, of those that are, that they are, and of those that are not, that they are not.” You have read this, I suppose? THEAETETUS: Yes, and many times. SOCRATES: Does he not mean something like this: that as each thing appears to me, so it is to me, and as it appears to you, so it is in turn to you? And you and I are “man”? THEAETETUS: Indeed, that is what he says. SOCRATES: It is likely, however, that a wise man is not talking nonsense; so let us follow him. Does it not sometimes happen that when the same wind is blowing, one of us feels cold and the other does not? And one feels it slightly, and the other extremely? THEAETETUS: Very much so. SOCRATES: Shall we say then, at that time, that the wind itself in itself is cold or not cold? Or shall we believe Protagoras, that it is cold for the one who feels cold, and for the one who does not, it is not? THEAETETUS: It seems so. SOCRATES: And does it not also appear so to each of them? THEAETETUS: Yes. SOCRATES: And “appears” means “is perceived”? THEAETETUS: Yes, indeed. SOCRATES: Appearance, then, and perception are the same in the case of hot things and all such things. For as each person perceives things, so they also tend to be for each person. THEAETETUS: It seems so. SOCRATES: Perception, then, is always of what is, and is unerring, since it is knowledge. THEAETETUS: So it appears. SOCRATES: By the Graces, then, was Protagoras some all-wise man, and did he speak this in riddles to us, the common rabble, while telling the truth in secret to his disciples? THEAETETUS: What in the world do you mean by this, Socrates? SOCRATES: I will tell you a by no means ordinary theory: that nothing is one thing by itself, nor could you rightly call anything by any name or as being of any kind; but if you call it large, it will also appear small, and if heavy, light, and so with everything, as though nothing were one, nor anything, nor of any kind. Rather, from motion, change, and mixture with one another, all things arise which we say “are,” calling them so incorrectly; for nothing ever is, but is always becoming. And on this point let all the wise men in turn, except Parmenides, agree: Protagoras, Heraclitus, and Empedocles, and of the poets, the leaders of each kind of poetry, Epicharmus in comedy, and Homer in tragedy, who, by saying: “Oceanus, the origin of the gods, and mother Tethys,” has said that all things are the offspring of flow and motion. Or does he not seem to mean this? THEAETETUS: To me he does.

SOCRATES: Who then could still dispute with such a great army, and with Homer as its commander, without becoming ridiculous? THEAETETUS: It is not easy, Socrates. SOCRATES: Indeed not, Theaetetus. For the following are also sufficient proofs for this theory: that what seems to be and what becomes is provided by motion, whereas what is not and what perishes is provided by rest. For heat and fire, which indeed generate and govern all other things, are themselves generated from change and friction; and these two are motions. Or are these not the generations of fire? THEAETETUS: Indeed they are. SOCRATES: Furthermore, the class of animals also grows from these same things. THEAETETUS: How could it be otherwise? SOCRATES: And what of this? Is not the condition of bodies destroyed by rest and inactivity, but preserved for a long time by exercise and motion? THEAETETUS: Yes. SOCRATES: And does not the condition in the soul, through learning and practice, which are motions, acquire knowledge, and is preserved, and becomes better, whereas through rest, which is lack of practice and ignorance, it learns nothing and forgets what it has learned? THEAETETUS: Very much so. SOCRATES: Is motion, then, the good for both soul and body, and the opposite the bad? THEAETETUS: It seems so. SOCRATES: Shall I speak to you further of windless calms and still seas and all such things, that rest rots and destroys, while the other preserves? And to crown all these, I will bring in the “golden chain,” by which Homer means nothing other than the sun, and he makes it clear that as long as the revolution is moving and the sun, all things exist and are preserved among both gods and men; but if this should stand still as if bound, all things would be destroyed and, as the saying goes, everything would be turned upside down? THEAETETUS: To me at least, Socrates, they seem to make clear what you say. SOCRATES: Assume then, my excellent friend, in this way: first, regarding the eyes, that what you call white color is not itself some other thing outside your eyes, nor in your eyes, nor should you assign any place to it; for then it would already be in a certain position and at rest, and would not be in the process of becoming. THEAETETUS: But how then?