Str. This point, then, let us put down definitely as one of complete perplexity. But since being and not-being participate equally in the perplexity, there is now at last some hope that as either of them emerges more dimly or more clearly, so also will the other emerge. 
 If, however, we are able to see neither of them, we will at any rate push our discussion through between both of them at once as creditably as we can. Theaet. Good. Str. Let us, then, explain how we come to be constantly calling this same thing by many names. Theaet. What, for instance? Please give an example. Str. We speak of man, you know, and give him many additional designations; we attribute to him colors and forms and sizes and vices and virtues,
 and in all these cases and countless others we say not only that he is man, but we say he is good and numberless other things. So in the same way every single thing which we supposed to be one, we treat as many and call by many names. Theaet. True. Str. And it is in this way, I fancy, that we have provided a fine feast for youngsters and for old men whose learning has come to them late in life; for example, it is easy enough for anyone to grasp the notion that the many cannot possibly be one, nor the one many, and so, apparently, they take pleasure in saying that we must not call a man good,
 but must call the good good, and a man man. I fancy, Theaetetus, you often run across people who take such matters seriously; sometimes they are elderly men whose poverty of intellect makes them admire such quibbles, and who think this is a perfect mine of wisdom they have discovered. Those are here satirized who deny the possibillty of all except identical predication. Such were Antisthenes, Euthydemus, and Dionysodorus. The two last are probably those referred to as old men whose learning came late in life. Theaet. Certainly. Str. Then, to include in our discussion all those who have ever engaged in any talk whatsoever about being,
 let us address our present arguments to these men as well as to all those with whom we were conversing before, and let us employ the form of questions. Theaet. What are the arguments? Str. Shall we attribute neither being to rest and motion, nor any attribute to anything, but shall we in our discussions assume that they do not mingle and cannot participate in one another? Or shall we gather all things together, believing that they are capable of combining with one another? Or are some capable of it and others not? Which of these alternatives,
 Theaetetus, should we say is their choice? Theaet. I cannot answer these questions for them. Str. Then why did you not answer each separately and see what the result was in each case? Theaet. A good suggestion. Str. And let us, if you please, assume that they say first that nothing has any power to combine with anything else. Then motion and rest will have no share in being, will they? Theaet. No. Str. Well, then, will either of them be, if it has no share in being? Theaet. It will not. Str. See how by this admission everything is overturned at once, as it seems—the doctrine of those who advocate universal motion, that of the partisans of unity and rest, and that of the men who teach that all existing things are distributed into invariable and everlasting kinds. For all of these make use of being as an attribute. One party says that the universe is in motion, another that it is at rest. Theaet. Exactly. Str. And further, all who teach that things combine at one time and separate at another, whether infinite elements combine in unity and are derived from unity or finite elements separate and then unite, regardless of whether they say that these changes take place successively or without interruption, would be talking nonsense in all these doctrines, if there is no intermingling. Theaet. Quite right. Str. Then, too, the very men who forbid us to call anything by another name because it participates in the effect produced by another, would be made most especially ridiculous by this doctrine. Theaet. How so? Str. Because they are obliged in speaking of anything to use the expressions to be, apart, from the rest, by itself, and countless others; they are powerless to keep away from them or avoid working them into their discourse; and therefore there is no need of others to refute them, but, as the saying goes, their enemy and future opponent is of their own household whom they always carry about with them as they go, giving forth speech from within them, like the wonderful Eurycles. Eurycles was a ventriloquist and soothsayer of the fifth century, cf. Aristoph. Wasps 1019 Theaet. That is a remarkably accurate illustration Str. But what if we ascribe to all things the power of participation in one another? Theaet. Even I can dispose of that assumption. Str. How? Theaet. Because motion itself would be wholly at rest, and rest in turn would itself be in motion, if these two could be joined with one another. Str. But surely this at least is most absolutely impossible, that motion be at rest and rest be in motion? Theaet. Of course. Str. Then only the third possibility is left. Theaet. Yes. Str. And certainly one of these three must be true; either all things will mingle with one another, or none will do so, or some will and others will not. Theaet. Of course. Str. And certainly the first two were found to be impossible. Theaet. Yes. Str. Then everybody who wishes to answer correctly will adopt the remaining one of the three possibilities. Theaet. Precisely. Str. Now since some things will commingle and others will not,
 they are in much the same condition as the letters of the alphabet; for some of these do not fit each other, and others do. Theaet. Of course. Str. And the vowels, to a greater degree than the others, run through them all as a bond, so that without one of the vowels the other letters cannot be joined one to another. Theaet. Certainly. Str. Now does everybody know which letters can join with which others? Or does he who is to join them properly have need of art? Theaet. He has need of art. Str. What art? Theaet. The art of grammar. Str. And is not the same true in connection with high and
 low sounds? Is not he who has the art to know the sounds which mingle and those which do not, musical, and he who does not know unmusical? Theaet. Yes. Str. And we shall find similar conditions, then, in all the other arts and processes which are devoid of art? Theaet. Of course. Str. Now since we have agreed that the classes or genera also commingle with one another, or do not commingle, in the same way, must not he possess some science and proceed by the processes of reason who is to show correctly which of the classes harmonize with which, and which reject one another,
 and also if he is to show whether there are some elements extending through all and holding them together so that they can mingle, and again, when they separate, whether there are other universal causes of separation? Theaet. Certainly he needs science, and perhaps even the greatest of sciences. Str. Then, Theaetetus, what name shall we give to this science? Or, by Zeus, have we unwittingly stumbled upon the science that belongs to free men and perhaps found the philosopher while we were looking for the sophist? Theaet. What do you mean? Str. Shall we not say that the division of things by classes and the avoidance of the belief that the same class is another, or another the same, belongs to the science of dialectic? Theaet. Yes, we shall. Str. Then he who is able to do this has a clear perception of one form or idea extending entirely through many individuals each of which lies apart, and of many forms differing from one another but included in one greater form, and again of one form evolved by the union of many wholes,
 and of many forms entirely apart and separate. This is the knowledge and ability to distinguish by classes how individual things can or cannot be associated with one another. Theaet. Certainly it is. Str. But you surely, I suppose, will not grant the art of dialectic to any but the man who pursues philosophy in purity and righteousness. Theaet. How could it be granted to anyone else?