SOC. And so should I. But since this is the case, and we have plenty of time, shall we not quietly, without any impatience, but truly examining ourselves,

 
consider again the nature of these appearances within us? And as we consider them, I shall say, I think, first, that nothing can ever become more or less in size or number, so long as it remains equal to itself. Is it not so? THEAET. Yes. SOC. And secondly, that anything to which nothing is added and from which nothing is subtracted, is neither increased nor diminished, but is always equal. THEAET. Certainly. SOC. And should we not say thirdly, that what was not previously could not afterwards be without becoming and having become? THEAET. Yes, I agree. SOC. These three assumptions contend with one another in our minds when we talk about the dice, or when we say that I, who do not, at my age, either increase in size or diminish, am in the course of a year first larger than you, who are young, and afterwards smaller, when nothing has been taken from my size,
 
but you have grown. For I am, it seems, afterwards what I was not before, and I have not become so; for it is impossible to have become without becoming, and without losing anything of my size I could not become smaller. And there are countless myriads of such contradictions, if we are to accept these that I have mentioned. You follow me, I take it, Theaetetus, for I think you are not new at such things. THEAET. By the gods, Socrates, I am lost in wonder when I think of all these things, and sometimes when I regard them it really makes my head swim. SOC. Theodorus seems to be a pretty good guesser about your nature. For this feeling of wonder shows that you are a philosopher, since wonder is the only beginning of philosophy, and he who said that Iris was the child of Thaumas Hes. Theog. 750 Iris is the messenger of heaven, and Plato interprets the name of her father as Wonder ( θαῦμα ). made a good genealogy. But do you begin to understand why these things are so, according to the doctrine we attribute to Protagoras, or do you not as yet? THEAET. Not yet, I think. SOC. And will you be grateful to me if I help you
 
to search out the hidden truth of the thought of a famous man or, I should say, of famous men? THEAET. Of course I shall be grateful, very grateful. SOC. Look round and see that none of the uninitiated is listening. The uninitiated are those who think nothing is except what they can grasp firmly with their hands, and who deny the existence of actions and generation and all that is invisible. THEAET. Truly, Socrates, those you speak of are very stubborn

 
and perverse mortals. SOC. So they are, my boy, quite without culture. But others are more clever, whose secret doctrines I am going to disclose to you. For them the beginning, upon which all the things we were just now speaking of depend, is the assumption that everything is real motion and that there is nothing besides this, but that there are two kinds of motion, each infinite in the number of its manifestations, and of these kinds one has an active, the other a passive force. From the union and friction of these two are born offspring, infinite in number, but always twins, the object of sense
 
and the sense which is always born and brought forth together with the object of sense. Now we give the senses names like these: sight and hearing and smell, and the sense of cold and of heat, and pleasures and pains and desires and fears and so forth. Those that have names are very numerous, and those that are unnamed are innumerable. Now the class of objects of sense is akin to each of these; all sorts of colors are akin to all sorts of acts of vision, and in the same way sounds to acts of hearing,
 
and the other objects of sense spring forth akin to the other senses. What does this tale mean for us, Theaetetus, with reference to what was said before? Do you see? THEAET. Not quite, Socrates. SOC. Just listen; perhaps we can finish the tale. It means, of course, that all these things are, as we were saying, in motion, and their motion has in it either swiftness or slowness. Now the slow element keeps its motion in the same place and directed towards such things as draw near it, and indeed it is in this way that it begets. 
 
But the things begotten in this way are quicker; for they move from one place to another, and their motion is naturally from one place to another. Now when the eye and some appropriate object which approaches beget whiteness and the corresponding perception—which could never have been produced by either of them going to anything else—then, while sight from the eye and
 
whiteness from that which helps to produce the color are moving from one to the other, the eye becomes full of sight and so begins at that moment to see, and becomes, certainly not sight, but a seeing eye, and the object which joined in begetting the color is filled with whiteness and becomes in its turn, not whiteness, but white, whether it be a stick or a stone, or whatever it be the hue of which is so colored. SOC. And all the rest—hard and hot and so forth—must be regarded in the same way: we must assume,

 
we said before, that nothing exists in itself, but all things of all sorts arise out of motion by intercourse with each other; for it is, as they say, impossible to form a firm conception of the active or the passive element as being anything separately; for there is no active element until there is a union with the passive element, nor is there a passive element until there is a union with the active; and that which unites with one thing is active and appears again as passive when it comes in contact with something else. And so it results from all this, as we said in the beginning, that nothing exists as invariably one, itself by itself, but everything is always becoming in relation to something, and being should be altogether abolished,
 
though we have often—and even just now—been compelled by custom and ignorance to use the word. But we ought not, the wise men say, to permit the use of something or somebody’s or mine or this or that or any other word that implies making things stand still, but in accordance with nature we should speak of things as becoming and being made and being destroyed and changing ; for anyone who by his mode of speech makes things stand still is easily refuted. And we must use such expressions in relation both to particular objects and collective designations, among which are
 
 mankind and stone and the names of every animal and class. Do these doctrines seem pleasant to you, Theaetetus, and do you find their taste agreeable? THEAET. I don’t know, Socrates; besides, I can’t tell about you, either, whether you are preaching them because you believe them or to test me. SOC. You forget, my friend, that I myself know nothing about such things, and claim none of them as mine, but am incapable of bearing them and am merely acting as a midwife to you, and for that reason am uttering incantations and giving you a taste of each of the philosophical theories,
 
until I may help to bring your own opinion to light. And when it is brought to light, I will examine it and see whether it is a mere wind-egg or a real offspring. So be brave and patient, and in good and manly fashion tell what you think in reply to my questions. THEAET. Very well; ask them. SOC. Then say once more whether the doctrine pleases you that nothing is, but is always becoming—good or beautiful or any of the other qualities we were just enumerating. THEAET. Why, when I hear you telling about it as you did, it seems to me that it is wonderfully reasonable and ought to be accepted as you have presented it. SOC. Let us, then, not neglect a point in which it is defective. The defect is found in connection with dreams and diseases, including insanity, and everything else that is said to cause illusions of sight and hearing and the other senses. For of course you know that in all these the doctrine we were just presenting seems admittedly to be refuted, because

 
in them we certainly have false perceptions, and it is by no means true that everything is to each man which appears to him; on the contrary, nothing is which appears. THEAET. What you say is very true, Socrates. SOC. What argument is left, then, my boy, for the man who says that perception is knowledge and that in each case the things which appear are to the one to whom they appear? THEAET. I hesitate to say, Socrates, that I have no reply to make, because you scolded me just now when I said that. 
 
But really I cannot dispute that those who are insane or dreaming have false opinions, when some of them think they are gods and others fancy in their sleep that they have wings and are flying. SOC. Don’t you remember, either, the similar dispute about these errors, especially about sleeping and waking? THEAET. What dispute? SOC. One which I fancy you have often heard. The question is asked, what proof you could give if anyone should ask us now, at the present moment, whether we are asleep and our thoughts are a dream, or whether we are awake
 
and talking with each other in a waking condition. THEAET. Really, Socrates, I don’t see what proof can be given; for there is an exact correspondence in all particulars, as between the strophe and antistrophe of a choral song. Take, for instance, the conversation we have just had: there is nothing to prevent us from imagining in our sleep also that we are carrying on this conversation with each other, and when in a dream we imagine that we are relating dreams, the likeness between the one talk and the other is remarkable. SOC. So you see it is not hard to dispute the point, since it is even open to dispute whether we are awake or in a dream. 
 
Now since the time during which we are asleep is equal to that during which we are awake, in each state our spirit contends that the semblances that appear to it at any time are certainly true, so that for half the time we say that this is true, and for half the time the other, and we maintain each with equal confidence. THEAET. Certainly. SOC. And may not, then, the same be said about insanity and the other diseases, except that the time is not equal? THEAET. Yes. SOC. Well, then, shall truth be determined by the length or shortness of time? THEAET. That would be absurd in many ways. SOC. But can you show clearly in any other way which of the two sets of opinions is true? THEAET. I do not think I can. SOC. Listen, then, while I tell you what would be said about them by those who maintain that what appears at any time is true for him to whom it appears. They begin, I imagine, by asking this question: Theaetetus, can that which is wholly other have in any way the same quality as its alternative? And we must not assume that the thing in question is partially the same and partially other, but wholly other.