Theaetetus · Plato
EUCLID'S SERVANT READS.
SOCRATES: Then examine we must, since you, who were so reluctant to begin, are so eager to proceed. The nature of motion appears to be the question with which we begin. What do they mean when they say that all things are in motion? Is there only one kind of motion, or, as I rather incline to think, two? I should like to have your opinion upon this point in addition to my own, that I may err, if I must err, in your company; tell me, then, when a thing changes from one place to another, or goes round in the same place, is not that what is called motion? THEODORUS: Yes. SOCRATES: Here then we have one kind of motion. But when a thing, remaining on the same spot, grows old, or becomes black from being white, or hard from being soft, or undergoes any other change, may not this be properly called motion of another kind? THEODORUS: I think so. SOCRATES: Say rather that it must be so. Of motion then there are these two kinds, 'change,' and 'motion in place.' THEODORUS: You are right. SOCRATES: And now, having made this distinction, let us address ourselves to those who say that all is motion, and ask them whether all things according to them have the two kinds of motion, and are changed as well as move in place, or is one thing moved in both ways, and another in one only?
THEODORUS: Indeed, I do not know what to answer; but I think they would say that all things are moved in both ways. SOCRATES: Yes, comrade; for, if not, they would have to say that the same things are in motion and at rest, and there would be no more truth in saying that all things are in motion, than that all things are at rest. THEODORUS: To be sure. SOCRATES: And if they are to be in motion, and nothing is to be devoid of motion, all things must always have every sort of motion? THEODORUS: Most true. SOCRATES: Consider a further point: did we not understand them to explain the generation of heat, whiteness, or anything else, in some such manner as the following:--were they not saying that each of them is moving between the agent and the patient, together with a perception, and that the patient ceases to be a perceiving power and becomes a percipient, and the agent a quale instead of a quality? I suspect that quality may appear a strange and uncouth term to you, and that you do not understand the abstract expression. Then I will take concrete instances: I mean to say that the producing power or agent becomes neither heat nor whiteness but hot and white, and the like of other things. For I must repeat what I said before, that neither the agent nor patient have any absolute existence, but when they come together and generate sensations and their objects, the one becomes a thing of a certain quality, and the other a percipient. You remember?
THEODORUS: Of course. SOCRATES: We may leave the details of their theory unexamined, but we must not forget to ask them the only question with which we are concerned: Are all things in motion and flux? THEODORUS: Yes, they will reply. SOCRATES: And they are moved in both those ways which we distinguished, that is to say, they move in place and are also changed? THEODORUS: Of course, if the motion is to be perfect. SOCRATES: If they only moved in place and were not changed, we should be able to say what is the nature of the things which are in motion and flux? THEODORUS: Exactly. SOCRATES: But now, since not even white continues to flow white, and whiteness itself is a flux or change which is passing into another colour, and is never to be caught standing still, can the name of any colour be rightly used at all? THEODORUS: How is that possible, Socrates, either in the case of this or of any other quality--if while we are using the word the object is escaping in the flux? SOCRATES: And what would you say of perceptions, such as sight and hearing, or any other kind of perception? Is there any stopping in the act of seeing and hearing? THEODORUS: Certainly not, if all things are in motion.
SOCRATES: Then we must not speak of seeing any more than of not-seeing, nor of any other perception more than of any non-perception, if all things partake of every kind of motion? THEODORUS: Certainly not. SOCRATES: Yet perception is knowledge: so at least Theaetetus and I were saying. THEODORUS: Very true. SOCRATES: Then when we were asked what is knowledge, we no more answered what is knowledge than what is not knowledge? THEODORUS: I suppose not. SOCRATES: Here, then, is a fine result: we corrected our first answer in our eagerness to prove that nothing is at rest. But if nothing is at rest, every answer upon whatever subject is equally right: you may say that a thing is or is not thus; or, if you prefer, 'becomes' thus; and if we say 'becomes,' we shall not then hamper them with words expressive of rest. THEODORUS: Quite true. SOCRATES: Yes, Theodorus, except in saying 'thus' and 'not thus.' But you ought not to use the word 'thus,' for there is no motion in 'thus' or in 'not thus.' The maintainers of the doctrine have as yet no words in which to express themselves, and must get a new language. I know of no word that will suit them, except perhaps 'no how,' which is perfectly indefinite. THEODORUS: Yes, that is a manner of speaking in which they will be quite at home.
SOCRATES: And so, Theodorus, we have got rid of your friend without assenting to his doctrine, that every man is the measure of all things--a wise man only is a measure; neither can we allow that knowledge is perception, certainly not on the hypothesis of a perpetual flux, unless perchance our friend Theaetetus is able to convince us that it is. THEODORUS: Very good, Socrates; and now that the argument about the doctrine of Protagoras has been completed, I am absolved from answering; for this was the agreement. THEAETETUS: Not, Theodorus, until you and Socrates have discussed the doctrine of those who say that all things are at rest, as you were proposing. THEODORUS: You, Theaetetus, who are a young rogue, must not instigate your elders to a breach of faith, but should prepare to answer Socrates in the remainder of the argument. THEAETETUS: Yes, if he wishes; but I would rather have heard about the doctrine of rest. THEODORUS: Invite Socrates to an argument--invite horsemen to the open plain; do but ask him, and he will answer. SOCRATES: Nevertheless, Theodorus, I am afraid that I shall not be able to comply with the request of Theaetetus. THEODORUS: Not comply! for what reason?
SOCRATES: My reason is that I have a kind of reverence; not so much for Melissus and the others, who say that 'All is one and at rest,' as for the great leader himself, Parmenides, venerable and awful, as in Homeric language he may be called;--him I should be ashamed to approach in a spirit unworthy of him. I met him when he was an old man, and I was a mere youth, and he appeared to me to have a glorious depth of mind. And I am afraid that we may not understand his words, and may be still further from understanding his meaning; above all I fear that the nature of knowledge, which is the main subject of our discussion, may be thrust out of sight by the unbidden guests who will come pouring in upon our feast of discourse, if we let them in--besides, the question which is now stirring is of immense extent, and will be treated unfairly if only considered by the way; or if treated adequately and at length, will put into the shade the other question of knowledge. Neither the one nor the other can be allowed; but I must try by my art of midwifery to deliver Theaetetus of his conceptions about knowledge. THEAETETUS: Very well; do so if you will. SOCRATES: Then now, Theaetetus, take another view of the subject: you answered that knowledge is perception?
THEAETETUS: I did. SOCRATES: And if any one were to ask you: With what does a man see black and white colours? and with what does he hear high and low sounds?--you would say, if I am not mistaken, 'With the eyes and with the ears.' THEAETETUS: I should. SOCRATES: The free use of words and phrases, rather than minute precision, is generally characteristic of a liberal education, and the opposite is pedantic; but sometimes precision is necessary, and I believe that the answer which you have just given is open to the charge of incorrectness; for which is more correct, to say that we see or hear with the eyes and with the ears, or through the eyes and through the ears. THEAETETUS: I should say 'through,' Socrates, rather than 'with.' SOCRATES: Yes, my boy, for no one can suppose that in each of us, as in a sort of Trojan horse, there are perched a number of unconnected senses, which do not all meet in some one nature, the mind, or whatever we please to call it, of which they are the instruments, and with which through them we perceive objects of sense. THEAETETUS: I agree with you in that opinion. SOCRATES: The reason why I am thus precise is, because I want to know whether, when we perceive black and white through the eyes, and again, other qualities through other organs, we do not perceive them with one and the same part of ourselves, and, if you were asked, you might refer all such perceptions to the body. Perhaps, however, I had better allow you to answer for yourself and not interfere. Tell me, then, are not the organs through which you perceive warm and hard and light and sweet, organs of the body?
THEAETETUS: Of the body, certainly. SOCRATES: And you would admit that what you perceive through one faculty you cannot perceive through another; the objects of hearing, for example, cannot be perceived through sight, or the objects of sight through hearing? THEAETETUS: Of course not. SOCRATES: If you have any thought about both of them, this common perception cannot come to you, either through the one or the other organ? THEAETETUS: It cannot. SOCRATES: How about sounds and colours: in the first place you would admit that they both exist? THEAETETUS: Yes. SOCRATES: And that either of them is different from the other, and the same with itself? THEAETETUS: Certainly. SOCRATES: And that both are two and each of them one? THEAETETUS: Yes. SOCRATES: You can further observe whether they are like or unlike one another? THEAETETUS: I dare say. SOCRATES: But through what do you perceive all this about them? for neither through hearing nor yet through seeing can you apprehend that which they have in common. Let me give you an illustration of the point at issue:--If there were any meaning in asking whether sounds and colours are saline or not, you would be able to tell me what faculty would consider the question. It would not be sight or hearing, but some other. THEAETETUS: Certainly; the faculty of taste.
SOCRATES: Very good; and now tell me what is the power which discerns, not only in sensible objects, but in all things, universal notions, such as those which are called being and not-being, and those others about which we were just asking--what organs will you assign for the perception of these notions? THEAETETUS: You are thinking of being and not being, likeness and unlikeness, sameness and difference, and also of unity and other numbers which are applied to objects of sense; and you mean to ask, through what bodily organ the soul perceives odd and even numbers and other arithmetical conceptions. SOCRATES: You follow me excellently, Theaetetus; that is precisely what I am asking. THEAETETUS: Indeed, Socrates, I cannot answer; my only notion is, that these, unlike objects of sense, have no separate organ, but that the mind, by a power of her own, contemplates the universals in all things. SOCRATES: You are a beauty, Theaetetus, and not ugly, as Theodorus was saying; for he who utters the beautiful is himself beautiful and good. And besides being beautiful, you have done me a kindness in releasing me from a very long discussion, if you are clear that the soul views some things by herself and others through the bodily organs. For that was my own opinion, and I wanted you to agree with me.
THEAETETUS: I am quite clear. SOCRATES: And to which class would you refer being or essence; for this, of all our notions, is the most universal? THEAETETUS: I should say, to that class which the soul aspires to know of herself. SOCRATES: And would you say this also of like and unlike, same and other? THEAETETUS: Yes. SOCRATES: And would you say the same of the noble and base, and of good and evil? THEAETETUS: These I conceive to be notions which are essentially relative, and which the soul also perceives by comparing in herself things past and present with the future. SOCRATES: And does she not perceive the hardness of that which is hard by the touch, and the softness of that which is soft equally by the touch? THEAETETUS: Yes. SOCRATES: But their essence and what they are, and their opposition to one another, and the essential nature of this opposition, the soul herself endeavours to decide for us by the review and comparison of them? THEAETETUS: Certainly. SOCRATES: The simple sensations which reach the soul through the body are given at birth to men and animals by nature, but their reflections on the being and use of them are slowly and hardly gained, if they are ever gained, by education and long experience. THEAETETUS: Assuredly. SOCRATES: And can a man attain truth who fails of attaining being?
THEAETETUS: Impossible. SOCRATES: And can he who misses the truth of anything, have a knowledge of that thing? THEAETETUS: He cannot. SOCRATES: Then knowledge does not consist in impressions of sense, but in reasoning about them; in that only, and not in the mere impression, truth and being can be attained? THEAETETUS: Clearly. SOCRATES: And would you call the two processes by the same name, when there is so great a difference between them? THEAETETUS: That would certainly not be right. SOCRATES: And what name would you give to seeing, hearing, smelling, being cold and being hot? THEAETETUS: I should call all of them perceiving--what other name could be given to them? SOCRATES: Perception would be the collective name of them? THEAETETUS: Certainly. SOCRATES: Which, as we say, has no part in the attainment of truth any more than of being? THEAETETUS: Certainly not. SOCRATES: And therefore not in science or knowledge? THEAETETUS: No. SOCRATES: Then perception, Theaetetus, can never be the same as knowledge or science? THEAETETUS: Clearly not, Socrates; and knowledge has now been most distinctly proved to be different from perception. SOCRATES: But the original aim of our discussion was to find out rather what knowledge is than what it is not; at the same time we have made some progress, for we no longer seek for knowledge in perception at all, but in that other process, however called, in which the mind is alone and engaged with being.
THEAETETUS: You mean, Socrates, if I am not mistaken, what is called thinking or opining. SOCRATES: You conceive truly. And now, my friend, please to begin again at this point; and having wiped out of your memory all that has preceded, see if you have arrived at any clearer view, and once more say what is knowledge. THEAETETUS: I cannot say, Socrates, that all opinion is knowledge, because there may be a false opinion; but I will venture to assert, that knowledge is true opinion: let this then be my reply; and if this is hereafter disproved, I must try to find another. SOCRATES: That is the way in which you ought to answer, Theaetetus, and not in your former hesitating strain, for if we are bold we shall gain one of two advantages; either we shall find what we seek, or we shall be less likely to think that we know what we do not know--in either case we shall be richly rewarded. And now, what are you saying?--Are there two sorts of opinion, one true and the other false; and do you define knowledge to be the true? THEAETETUS: Yes, according to my present view. SOCRATES: Is it still worth our while to resume the discussion touching opinion? THEAETETUS: To what are you alluding? SOCRATES: There is a point which often troubles me, and is a great perplexity to me, both in regard to myself and others. I cannot make out the nature or origin of the mental experience to which I refer.
THEAETETUS: Pray what is it? SOCRATES: How there can be false opinion--that difficulty still troubles the eye of my mind; and I am uncertain whether I shall leave the question, or begin over again in a new way. THEAETETUS: Begin again, Socrates,--at least if you think that there is the slightest necessity for doing so. Were not you and Theodorus just now remarking very truly, that in discussions of this kind we may take our own time? SOCRATES: You are quite right, and perhaps there will be no harm in retracing our steps and beginning again. Better a little which is well done, than a great deal imperfectly. THEAETETUS: Certainly. SOCRATES: Well, and what is the difficulty? Do we not speak of false opinion, and say that one man holds a false and another a true opinion, as though there were some natural distinction between them? THEAETETUS: We certainly say so. SOCRATES: All things and everything are either known or not known. I leave out of view the intermediate conceptions of learning and forgetting, because they have nothing to do with our present question. THEAETETUS: There can be no doubt, Socrates, if you exclude these, that there is no other alternative but knowing or not knowing a thing. SOCRATES: 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?
THEAETETUS: He must. SOCRATES: He who knows, cannot but know; and he who does not know, cannot know? THEAETETUS: Of course. SOCRATES: 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? THEAETETUS: That, Socrates, is impossible. SOCRATES: 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? THEAETETUS: How can he? SOCRATES: 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? THEAETETUS: That would be monstrous. SOCRATES: 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. THEAETETUS: Most true. SOCRATES: Suppose that we remove the question out of the sphere of knowing or not knowing, into that of being and not-being. THEAETETUS: What do you mean? SOCRATES: 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?
THEAETETUS: That, again, is not unlikely, Socrates. SOCRATES: 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? THEAETETUS: Yes. SOCRATES: But is there any parallel to this? THEAETETUS: What do you mean? SOCRATES: Can a man see something and yet see nothing? THEAETETUS: Impossible. SOCRATES: 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 non-existing things? THEAETETUS: I do not. SOCRATES: He then who sees some one thing, sees something which is? THEAETETUS: Clearly. SOCRATES: And he who hears anything, hears some one thing, and hears that which is? THEAETETUS: Yes. SOCRATES: And he who touches anything, touches something which is one and therefore is? THEAETETUS: That again is true. SOCRATES: And does not he who thinks, think some one thing? THEAETETUS: Certainly. SOCRATES: And does not he who thinks some one thing, think something which is? THEAETETUS: I agree. SOCRATES: Then he who thinks of that which is not, thinks of nothing? THEAETETUS: Clearly. SOCRATES: And he who thinks of nothing, does not think at all?
THEAETETUS: Obviously. SOCRATES: Then no one can think that which is not, either as a self-existent substance or as a predicate of something else? THEAETETUS: Clearly not. SOCRATES: Then to think falsely is different from thinking that which is not? THEAETETUS: It would seem so. SOCRATES: Then false opinion has no existence in us, either in the sphere of being or of knowledge? THEAETETUS: Certainly not. SOCRATES: But may not the following be the description of what we express by this name? THEAETETUS: What? SOCRATES: 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. THEAETETUS: 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. SOCRATES: I see, Theaetetus, that your fear has disappeared, and that you are beginning to despise me. THEAETETUS: What makes you say so? SOCRATES: 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?
THEAETETUS: I am. SOCRATES: It is possible then upon your view for the mind to conceive of one thing as another? THEAETETUS: True. SOCRATES: But must not the mind, or thinking power, which misplaces them, have a conception either of both objects or of one of them? THEAETETUS: Certainly. SOCRATES: Either together or in succession? THEAETETUS: Very good. SOCRATES: And do you mean by conceiving, the same which I mean? THEAETETUS: What is that? SOCRATES: 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? THEAETETUS: I agree. SOCRATES: Then when any one thinks of one thing as another, he is saying to himself that one thing is another? THEAETETUS: Yes. SOCRATES: 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?
Ideas discussed in this chapter
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