SOC. And therefore he who hears anything, hears some one thing and therefore hears what is. THEAET. Yes. SOC. And he who touches anything, touches some one thing, which is, since it is one? THEAET. That also is true. SOC. So, then, does not he who holds an opinion hold an opinion of some one thing? THEAET. He must do so. SOC. And does not he who holds an opinion of some one thing hold an opinion of something that is? THEAET. I agree. SOC. Then he who holds an opinion of what is not holds an opinion of nothing. THEAET. Evidently. SOC. Well then, he who holds an opinion of nothing, holds no opinion at all. THEAET. That is plain, apparently. SOC. Then it is impossible to hold an opinion of that which is not, either in relation to things that are, or independently of them. THEAET. Evidently. SOC. Then holding false opinion is something different from holding an opinion of that which is not? THEAET. So it seems. SOC. Then false opinion is not found to exist in us either by this method or by that which we followed a little while ago. THEAET. No, it certainly is not. SOC. But does not that which we call by that name arise after the following manner? THEAET. After what manner? SOC. We say that false opinion is a kind of interchanged opinion,
 
when a person makes an exchange in his mind and says that one thing which exists is another thing which exists. For in this way he always holds an opinion of what exists, but of one thing instead of another; so he misses the object he was aiming at in his thought and might fairly be said to hold a false opinion. THEAET. Now you seem to me to have said what is perfectly right. For when a man, in forming an opinion, puts ugly instead of beautiful, or beautiful instead of ugly, he does truly hold a false opinion. SOC. Evidently, Theaetetus, you feel contempt of me, and not fear. THEAET. Why in the world do you say that? SOC. You think, I fancy, that I would not attack your truly false 
 
by asking whether it is possible for a thing to become slowly quick or heavily light, or any other opposite, by a process opposite to itself, in accordance, not with its own nature, but with that of its opposite. But I let this pass, that your courage may not fail. You are satisfied, you say, that false opinion is interchanged opinion? THEAET. I am. SOC. It is, then, in your opinion, possible for the mind to regard one thing as another and not as what it is. THEAET. Yes, it is. SOC. Now when one’s mind does this, does it not necessarily
 
have a thought either of both things together or of one or the other of them? THEAET. Yes, it must; either of both at the same time or in succession. SOC. Excellent. And do you define thought as I do? THEAET. How do you define it?