Str. Yes, and the sophist is nothing else, apparently, than the money-making class of the disputatious, argumentative, controversial, pugnacious, combative, acquisitive art, as our argument has now again stated. Theaet. Certainly. Str. Do you see the truth of the statement that this creature is many-sided and, as the saying is, not to be caught with one hand? Theaet. Then we must catch him with both. Str. Yes, we must, and must go at it with all our might,
 by following another track of his—in this way. Tell me; of the expressions connected with menial occupations some are in common use, are they not? Theaet. Yes, many. But to which of the many does your question refer? Str. To such as these: we say sift and strain and winnow and separate. Apparently a term descriptive of some part of the process of weaving; cf. Plat. Crat. 338b . Theaet. Certainly. Str. And besides these there are card and comb and beat the web and countless other technical terms which we know. Is it not so? Theaet. Why do you use these as examples and ask about them all? 
 What do you wish to show in regard to them? Str. All those that I have mentioned imply a notion of division. Theaet. Yes. Str. Then since there is, accorling to my reckoning, one art involved in all of these operations, let us give it one name. Theaet. What shall we call it? Str. The art of discrimination. Theaet. Very well. Str. Now see if we can discover two divisions of this. Theaet. You demand quick thinking, for a boy like me. Str. And yet, in the instance of discrimination just mentioned there was, first, the separation of worse from better, and, secondly, of like from like. Theaet. Yes, as you now express it, that is pretty clear. Str. Now I know no common name for the second kind of discrimination; but I do know the name of the kind which retains the better and throws away the worse. Theaet. What is it? Str. Every such discrimination, as I think, is universally called a sort of purification. Theaet. Yes, so it is. Str. And could not anyone see that purification is of two kinds? Theaet. Yes, perhaps, in time; but still I do not see it now. Str. Still there are many kinds of purifications of bodies, and they may all properly be included under one name. Theaet. What are they and what is the name? Str. The purification of living creatures, having to do with impurities within the body, such as are successfully discriminated by gymnastics and medicine,
 and with those outside of the body, not nice to speak of, such as are attended to by the bath-keeper’s art; and the purification of inanimate bodies, which is the special care of the fuller’s art and in general of the art of exterior decoration; this, with its petty subdivisions, has taken on many names which seem ridiculous. Theaet. Very. Str. Certainly they do, Theaetetus. However, the method of argument is neither more nor less concerned with the art of medicine than with that of sponging, but is indifferent if the one benefits us little, the other greatly by its purifying. 
 It endeavors to understand what is related and what is not related in all arts, for the purpose of acquiring intelligence; and therefore it honors them all equally and does not in making comparisons think one more ridiculous than another, and does not consider him who employs, as his example of hunting, the art of generalship, any more dignified than him who employs the art of louse-catching, but only, for the most part, as more pretentious. And now as to your question, what name we shall give to all the activities whose function it is to purify the body, whether animate or inanimate, it will not matter at all to our method
 what name sounds finest; it cares only to unite under one name all purifications of everything else and to keep them separate from the purification of the soul. For it has in our present discussion been trying to separate this purification definitely from the rest, if we understand its desire. Theaet. But I do understand and I agree that there are two kinds of purification and that one kind is the purification of the soul, which is separate from that of the body. Str. Most excellent. Now pay attention to the next point
 and try again to divide the term. Theaet. In whatever way you suggest, I will try to help you in making the division. Str. Do we say that wickedness is distinct from virtue in the soul? Theaet. Of course. Str. And purification was retaining the one and throwing out whatever is bad anywhere? Theaet. Yes, it was. Str. Hence whenever we find any removal of evil from the soul, we shall be speaking properly if we call that a purification. Theaet. Very properly. Str. We must say that there are two kinds of evil in the soul. Theaet. What kinds? Str. The one is comparable to a disease in the body, the other to a deformity. Theaet. I do not understand. Str. Perhaps you have not considered that disease and discord are the same thing? Theaet. I do not know what reply I ought to make to this, either. Str. Is that because you think discord is anything else than the disagreement of the naturally related, brought about by some corruption? Theaet. No; I think it is nothing else. Str. But is deformity anything else than the presence of the quality of disproportion, which is always ugly? Theaet. Nothing else at all. Str. Well then; do we not see that in the souls of worthless men opinions are opposed to desires, anger to pleasures, reason to pain, and all such things to one another? Theaet. Yes, they are, decidedly. Str. Yet they must all be naturally related. Theaet. Of course. Str. Then we shall be right if we say that wickedness is a discord and disease of the soul. Theaet. Yes, quite right. Str. But if things which partake of motion and aim at some particular mark pass beside the mark and miss it on every occasion when they try to hit it, shall we say that this happens to them through right proportion to one another or, on the contrary, through disproportion? The connection between disproportion and missing the mark is not obvious. The explanation that a missile (e.g. an arrow) which is not evenly balanced will not fly straight, fails to take account of the words πρὸς ἄλληλα . The idea seems rather to be that moving objects of various sizes, shapes, and rates of speed must interfere with each other. Theaet. Evidently through disproportion. Str. But yet we know that every soul, if ignorant of anything, is ignorant against its will. Theaet. Very much so. Str. Now being ignorant is nothing else than
 the aberration of a soul that aims at truth, when the understanding passes beside the mark. Theaet. Very true. Str. Then we must regard a foolish soul as deformed and ill-proportioned. Theaet. So it seems. Str. Then there are, it appears, these two kinds of evils in the soul, one, which people call wickedness, which is very clearly a disease. Theaet. Yes. Str. And the other they call ignorance, but they are not willing to acknowledge that it is vice, when it arises only in the soul. Theaet. It must certainly be admitted, though I disputed it when you said it just now, that there are two kinds of vice in the soul, and that cowardice, intemperance, and injustice must all alike be considered a disease in us, and the widespread and various condition of ignorance must be regarded as a deformity. Str. In the case of the body there are two arts which have to do with these two evil conditions, are there not? Theaet. What are they? Str. For deformity there is gymnastics, and for disease medicine. Theaet. That is clear. Str. Hence for insolence and injustice and cowardice is not the corrective art the one of all arts most closely related to Justice? Theaet. Probably it is, at least according to the judgement of mankind. Str. And for all sorts of ignorance is there any art it would be more correct to suggest than that of instruction? Theaet. No, none. Str. Come now, think. Shall we say that
 there is only one kind of instruction, or that there are more and that two are the most important? Theaet. I am thinking. Str. I think we can find out most quickly in this way. Theaet. In what way? Str. By seeing whether ignorance admits of being cut in two in the middle; for if ignorance turns out to be twofold, it is clear that instruction must also consist of two parts, one for each part of ignorance. Theaet. Well, can you see what you are now looking for? Str. I at any rate think I do see one large and grievous kind of ignorance, separate from the rest, and as weighty as all the other parts put together. Theaet. What is it? Str. Thinking that one knows a thing when one does not know it. Through this, I believe, all the mistakes of the mind are caused in all of us. Theaet. True. Str. And furthermore to this kind of ignorance alone the name of stupidity is given. Theaet. Certainly. Str. Now what name is to be given to that part of instruction which gets rid of this? Theaet. I think, Stranger, that the other part is called instruction in handicraft, and that this part is here at Athens through our influence called education. Str. And so it is, Theaetetus, among nearly all the Hellenes. But we must examine further and see whether it is one and indivisible or still admits of division important enough to have a name. Theaet. Yes, we must see about that. Str. I think there is still a way in which this also may be divided. Theaet. On what principle? Str. Of instruction in arguments one method
 seems to be rougher, and the other section smoother. Theaet. What shall we call each of these? Str. The venerable method of our fathers, which they generally employed towards their sons, and which many still employ, of sometimes showing anger at their errors
 and sometimes more gently exhorting them—that would most properly be called as a whole admonition. Theaet. That is true. Str. On the other hand, some appear to have convinced themselves that all ignorance is involuntary, and that he who thinks himself wise would never be willing to learn any of those things in which he believes he is clever, and that the admonitory kind of education takes a deal of trouble and accomplishes little. Theaet. They are quite right. Str. So they set themselves to cast out the conceit of cleverness in another way. Theaet. In what way? Str. They question a man about the things about which he thinks he is talking sense when he is talking nonsense; then they easily discover that his opinions are like those of men who wander, and in their discussions they collect those opinions and compare them with one another, and by the comparison they show that they contradict one another about the same things, in relation to the same things and in respect to the same things. But those who see this grow angry with themselves and gentle towards others, and this is the way in which
 they are freed from their high and obstinate opinions about themselves. The process of freeing them, moreover, affords the greatest pleasure to the listeners and the most lasting benefit to him who is subjected to it. For just as physicians who care for the body believe that the body cannot get benefit from any food offered to it until all obstructions are removed, so, my boy, those who purge the soul believe that the soul can receive no benefit from any teachings offered to it
 until someone by cross-questioning reduces him who is cross-questioned to an attitude of modesty, by removing the opinions that obstruct the teachings, and thus purges him and makes him think that he knows only what he knows, and no more. Theaet. That is surely the best and most reasonable state of mind. Str. For all these reasons, Theaetetus, we must assert that cross-questioning is the greatest and most efficacious of all purifications, and that he who is not cross-questioned, even though he be the Great King,
 has not been purified of the greatest taints, and is therefore uneducated and deformed in those things in which he who is to be truly happy ought to be most pure and beautiful. Theaet. Perfectly true.