Theaet. There can be no doubt, Socrates, if you exclude these, that there is no other alternative but knowing or not knowing a thing.
Soc. That point being now determined, must we not say that he who has an opinion, must have an opinion about something which he knows or does not know ?
Theaet. He must.
Soc. He who knows, cannot but know ; and he who does not know, cannot know ?
Theaet. Of course.
Soc. What shall we say then ? When a man has a false opinion does he think that which he knows to be some other thing which he knows, and knowing both, is he at the same time ignorant of both ?
Theaet. That, Socrates, is impossible.
Soc. But perhaps he thinks of something which he does not know as some other thing which he does not know ; for example, he knows neither Theaetetus nor Socrates, and yet he fancies that Theaetetus is Socrates, or Socrates Theaetetus ?
Theaet. How can he ?
Soc. But surely he cannot suppose what he knows to be what he does not know, or what he does not know to be what he knows ?
Theaet. That would be monstrous.
Soc. Where, then, is false opinion ? For if all things are either known or unknown, there can be no opinion which is not comprehended under this alternative, and so false opinion is excluded.
Theaes. Most true.
Soc. Suppose that we remove the question out of the sphere of knowing or not knowing, into that of being and not-being.
Theaet. What do you mean ?
Soc. May we not suspect the simple truth to be that he who thinks about anything, that which. is not, will necessarily think what is false, whatever in other respects may be the state of his mind ?
Theaet. That, again, is not unlikely, Socrates.
Soc. Then suppose some one to say to us, Theaetetus : — Is it possible for any man to think that which is not, either as a self-existent substance or as a predicate of something else ? And suppose that we answer, “Yes, he can, when he thinks what is not true.” — That will be our answer ?
Theaet. Yes.
Soc. But is there any parallel to this ?
Theaet. What do you mean ?
Soc. Can a man see something and yet see nothing ?
Theaet. Impossible.
Soc. But if he sees any one thing, he sees something that exists. Do you suppose that what is one is ever to be found among nonexisting things ?
Theaet. I do not.
Soc. He then who sees some one thing, sees something which is ?
Theaet. Clearly.
Soc. And he who hears anything, hears some one thing, and hears that which is ?
Theaet. Yes.
Soc. And he who touches anything, touches something which is one and therefore is ?
Theaet. That again is true.
Soc. And does not he who thinks, think some one thing ?
Theaet. Certainly.
Soc. And does not he who thinks some one thing, think something which is ?
Theaet. I agree.
Soc. Then he who thinks of that which is not, thinks of nothing ?
Theaet. Clearly.
Soc. And he who thinks of nothing, does not think at all ?
Theaet. Obviously.
Soc. Then no one can think that which is not, either as a self-existent substance or as a predicate of something else ?
Theaet. Clearly not.
Soc. Then to think falsely is different from thinking that which is not ?
Theaet. It would seem so.
Soc. Then false opinion has no existence in us, either in the sphere of being or of knowledge ?
Theaet. Certainly not.
Soc. But may not the following be the description of what we express by this name ?
Theaet. What ?
Soc. May we not suppose that false opinion or thought is a sort of heterodoxy ; a person may make an exchange in his mind, and say that one real object is another real object. For thus he always thinks that which is, but he puts one thing in place of another ; and missing the aim of his thoughts, he may be truly said to have false opinion.
Theaet. Now you appear to me to have spoken the exact truth : when a man puts the base in the place of the noble, or the noble in the place of the base, then he has truly false opinion.
Soc. I see, Theaetetus, that your fear has disappeared, and that you are beginning to despise me.
Theaet. What makes you say so ?
Soc. You think, if I am not mistaken, that your “truly false” is safe from censure, and that I shall never ask whether there can be a swift which is slow, or a heavy which is light, or any other self-contradictory thing, which works, not according to its own nature, but according to that of its opposite. But I will not insist upon this, for I do not wish needlessly to discourage you. And so you are satisfied that false opinion is heterodoxy, or the thought of something else ?
Theaet. I am.
Soc. It is possible then upon your view for the mind to conceive of one thing as another ?
Theaet. True.
Soc. But must not the mind, or thinking power, which misplaces them, have a conception either of both objects or of one of them ?
Theaet. Certainly.
Soc. Either together or in succession ?
Theaet. Very good.
Soc. And do you mean by conceiving, the same which I mean ?
Theaet. What is that ?
Soc. I mean the conversation which the soul holds with herself in considering of anything. I speak of what I scarcely understand ; but the soul when thinking appears to me to be just talking — asking questions of herself and answering them, affirming and denying. And when she has arrived at a decision, either gradually or by a sudden impulse, and has at last agreed, and does not doubt, this is called her opinion. I say, then, that to form an opinion is to speak, and opinion is a word spoken, — I mean, to oneself and in silence, not aloud or to another : What think you ?
Theaet. I agree.
Soc. Then when any one thinks of one thing as another, he is saying to himself that one thing is another ?
Theaet. Yes.
Soc. But do you ever remember saying to yourself that the noble is certainly base, or the unjust just ; or, best of all — have you ever attempted to convince yourself that one thing is another ? Nay, not even in sleep, did you ever venture to say to yourself that odd is even, or anything of the kind ?
Theaet. Never.
Soc. And do you suppose that any other man, either in his senses or out of them, ever seriously tried to persuade himself that an ox is a horse, or that two are one ?
Theaet. Certainly not.
Soc. But if thinking is talking to oneself, no one speaking and thinking of two objects, and apprehending them both in his soul, will say and think that the one is the other of them, and I must add, that even you, lover of dispute as you are, had better let the word “other” alone [i.e., not insist that “one” and “other” are the same]. I mean to say, that no one thinks the noble to be base, or anything of the kind.
Theaet. I will give up the word “other,” Socrates ; and I agree to what you say.
Soc. If a man has both of them in his thoughts, he cannot think that the one of them is the other ?
Theat. True.
Soc. Neither, if he has one of them only in his mind and not the other, can he think that one is the other ?
Theaet. True ; for we should have to suppose that he apprehends that which is not in his thoughts at all.
Soc. Then no one who has either both or only one of the two objects in his mind can think that the one is the other. And therefore, he who maintains that false opinion is heterodoxy is talking nonsense ; for neither in this, any more than in the previous way, can false opinion exist in us.
Theaet. No.