Written ca. 360 B.C.
Translated by Benjamin Jowett
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Euclid: Have you only just arrived from the country, Terpsion?
Persons of the Dialogue
Euclid and Terpsion meet in front of Euclid's house in Megara; they enter the house, and the
dialogue is read to them by a servant.
Terpsion: No, I came some time ago: and I have been in the Agora looking for you, and
wondering that I could not find you.
Euclid: But I was not in the city.
Terpsion: Where then?
Euclid: As I was going down to the harbour, I met Theaetetus-he was being carried up to
Athens from the army at Corinth.
Terpsion: Was he alive or dead?
Euclid: He was scarcely alive, for he has been badly wounded; but he was suffering even more
from the sickness which has broken out in the army.
Terpsion: The dysentery, you mean?
Terpsion: Alas! what a loss he will be!
Euclid: Yes, Terpsion, he is a noble fellow; only to-day I heard some people highly praising his
behaviour in this very battle.
Terpsion: No wonder; I should rather be surprised at hearing anything else of him. But why did
he go on, instead of stopping at Megara?
Euclid: He wanted to get home: although I entreated and advised him to remain he would not
listen to me; so I set him on his way, and turned back, and then I remembered what Socrates
had said of him, and thought how remarkably this, like all his predictions, had been fulfilled. I
believe that he had seen him a little before his own death, when Theaetetus was a youth, and
he had a memorable conversation with him, which he repeated to me when I came to Athens;
he was full of admiration of his genius, and said that he would most certainly be a great man,
if he lived.
Terpsion: The prophecy has certainly been fulfilled; but what was the conversation? can you tell
Euclid: No, indeed, not offhand; but I took notes of it as soon as I got home; these I filled up
from memory, writing them out at leisure; and whenever I went to Athens, I asked Socrates
about any point which I had forgotten, and on my return I made corrections; thus I have
nearly the whole conversation written down.
Terpsion: I remember-you told me; and I have always been intending to ask you to show me the
writing, but have put off doing so; and now, why should we not read it through?-having just
come from the country, I should greatly like to rest.
Euclid: I too shall be very glad of a rest, for I went with Theaetetus as far as Erineum. Let us go
in, then, and, while we are reposing, the servant shall read to us.
Terpsion: Very good.
Euclid: Here is the roll, Terpsion; I may observe that I have introduced Socrates, not as
narrating to me, but as actually conversing with the persons whom he mentioned-these were,
Theodorus the geometrician (of Cyrene), and Theaetetus. I have omitted, for the sake of
convenience, the interlocutory words "I said," "I remarked," which he used when he spoke of
himself, and again, "he agreed," or "disagreed," in the answer, lest the repetition of them
should be troublesome.
Terpsion: Quite right, Euclid.
Euclid: And now, boy, you may take the roll and read.
Euclid's servant reads.
Socrates. If I cared enough about the Cyrenians, Theodorus, I would ask you whether there
are any rising geometricians or philosophers in that part of the world. But I am more
interested in our own Athenian youth, and I would rather know who among them are likely to
do well. I observe them as far as I can myself, and I enquire of any one whom they follow,
and I see that a great many of them follow you, in which they are quite right, considering your
eminence in geometry and in other ways. Tell me then, if you have met with any one who is
good for anything.
Theodorus. Yes, Socrates, I have become acquainted with one very remarkable Athenian
youth, whom I commend to you as well worthy of your attention. If he had been a beauty I
should have been afraid to praise him, lest you should suppose that I was in love with him;
but he is no beauty, and you must not be offended if I say that he is very like you; for he has a
snub nose and projecting eyes, although these features are less marked in him than in you.
Seeing, then, that he has no personal attractions, I may freely say, that in all my acquaintance,
which is very large, I never knew anyone who was his equal in natural gifts: for he has a
quickness of apprehension which is almost unrivalled, and he is exceedingly gentle, and also
the most courageous of men; there is a union of qualities in him such as I have never seen in
any other, and should scarcely have thought possible; for those who, like him, have quick and
ready and retentive wits, have generally also quick tempers; they are ships without ballast,
and go darting about, and are mad rather than courageous; and the steadier sort, when they
have to face study, prove stupid and cannot remember. Whereas he moves surely and
smoothly and successfully in the path of knowledge and enquiry; and he is full of gentleness,
flowing on silently like a river of oil; at his age, it is wonderful.
Socrates: That is good news; whose son is he?
Theodorus: The name of his father I have forgotten, but the youth himself is the middle one of
those who are approaching us; he and his companions have been anointing themselves in the
outer court, and now they seem to have finished, and are towards us. Look and see whether
you know him.
Socrates: I know the youth, but I do not know his name; he is the son of Euphronius the Sunian,
who was himself an eminent man, and such another as his son is, according to your account
of him; I believe that he left a considerable fortune.
Theodorus: Theaetetus, Socrates, is his name; but I rather think that the property disappeared in
the hands of trustees; notwithstanding which he is wonderfully liberal.
Socrates: He must be a fine fellow; tell him to come and sit by me.
Theodorus: I will. Come hither, Theaetetus, and sit by Socrates.
Socrates: By all means, Theaetetus, in order that I may see the reflection of myself in your face,
for Theodorus says that we are alike; and yet if each of us held in his hands a lyre, and he
said that they were, tuned alike, should we at once take his word, or should we ask whether
he who said so was or was not a musician?
Theaetetus. We should ask.
Socrates: And if we found that he was, we should take his word; and if not, not?
Socrates: And if this supposed, likeness of our faces is a matter of any interest to us we should
enquire whether he who says that we are alike is a painter or not?
Theaetetus: Certainly we should.
Socrates: And is Theodorus a painter?
Theaetetus: I never heard that he was.
Socrates: Is he a geometrician?
Theaetetus: Of course he is, Socrates.
Socrates: And is he an astronomer and calculator and musician, and in general an educated man?
Theaetetus: I think so.
Socrates: If, then, he remarks on a similarity in our persons, either by way of praise or blame,
there is no particular reason why we should attend to him.
Theaetetus: I should say not.
Socrates: But if he praises the virtue or wisdom which are the mental endowments of either of us,
then he who hears the praises will naturally desire to examine him who is praised: and he
again should be willing to exhibit himself.
Theaetetus: Very true, Socrates.
Socrates: Then now is the time, my dear Theaetetus, for me to examine, and for you to exhibit;
since although Theodorus has praised many a citizen and stranger in my hearing, never did I
hear him praise any one as he has been praising you.
Theaetetus: I am glad to hear it, Socrates; but what if he was only in jest?
Socrates: Nay, Theodorus is not given to jesting; and I cannot allow you to retract your consent
on any such pretence as that. If you do, he will have to swear to his words; and we are
perfectly sure that no one will be found to impugn him. Do not be shy then, but stand to your
Theaetetus: I suppose I must, if you wish it.
Socrates: In the first place, I should like to ask what you learn of Theodorus: something of
Socrates: And astronomy and harmony and calculation?
Theaetetus: I do my best.
Socrates: Yes, my boy, and so do I: and my desire is to learn of him, or of anybody who seems to
understand these things. And I get on pretty well in general; but there is a little difficulty which
I want you and the company to aid me in investigating. Will you answer me a question: "Is not
learning growing wiser about that which you learn?"
Theaetetus: Of course.
Socrates: And by wisdom the wise are wise?
Socrates: And is that different in any way from knowledge?
Socrates: Wisdom; are not men wise in that which they know?
Theaetetus: Certainly they are.
Socrates: Then wisdom and knowledge are the same?
Socrates: Herein lies the difficulty which I can never solve to my satisfaction-What is knowledge?
Can we answer that question? What say you? which of us will speak first? whoever misses
shall sit down, as at a game of ball, and shall be donkey, as the boys say; he who lasts out his
competitors in the game without missing, shall be our king, and shall have the right of putting
to us any questions which he pleases. .. Why is there no reply? I hope, Theodorus, that I am
not betrayed into rudeness by my love of conversation? I only want to make us talk and be
friendly and sociable.
Theodorus: The reverse of rudeness, Socrates: but I would rather that you would ask one of the
young fellows; for the truth is, that I am unused to your game of question and answer, and I
am too old to learn; the young will be more suitable, and they will improve more than I shall,
for youth is always able to improve. And so having made a beginning with Theaetetus, I
would advise you to go on with him and not let him off.
Socrates: Do you hear, Theaetetus, what Theodorus says? The philosopher, whom you would not
like to disobey, and whose word ought to be a command to a young man, bids me
interrogate you. Take courage, then, and nobly say what you think that knowledge is.
Theaetetus: Well, Socrates, I will answer as you and he bid me; and if make a mistake, you will
doubtless correct me.
Socrates: We will, if we can.
Theaetetus: Then, I think that the sciences which I learn from Theodorus-geometry, and those
which you just now mentioned-are knowledge; and I would include the art of the cobbler and
other craftsmen; these, each and all of, them, are knowledge.
Why is this initial definition given by Theaetetus insufficient?
Socrates: Too much, Theaetetus, too much; the nobility and liberality of your nature make you
give many and diverse things, when I am asking for one simple thing.
Theaetetus: What do you mean, Socrates?
Socrates: Perhaps nothing. I will endeavour, however, to explain what I believe to be my meaning:
When you speak of cobbling, you mean the art or science of making shoes?
Theaetetus: Just so.
Socrates: And when you speak of carpentering, you mean the art of making wooden implements?
Theaetetus: I do.
Socrates: In both cases you define the subject matter of each of the two arts?
Socrates: But that, Theaetetus, was not the point of my question: we wanted to know not the
subjects, nor yet the number of the arts or sciences, for we were not going to count them, but
we wanted to know the nature of knowledge in the abstract. Am I not right?
Theaetetus: Perfectly right.
Socrates: Let me offer an illustration: Suppose that a person were to ask about some very trivial
and obvious thing-for example, What is clay? and we were to reply, that there is a clay of
potters, there is a clay of oven-makers, there is a clay of brick-makers; would not the answer
Socrates: In the first place, there would be an absurdity in assuming that he who asked the
question would understand from our answer the nature of "clay," merely because we added
"of the image-makers," or of any other workers. How can a man understand the name of
anything, when he does not know the nature of it?
Theaetetus: He cannot.
Socrates: Then he who does not know what science or knowledge is, has no knowledge of the art
or science of making shoes?
Socrates: Nor of any other science?
Socrates: And when a man is asked what science or knowledge is, to give in answer the name of
some art or science is ridiculous; for the -question is, "What is knowledge?" and he replies,
"A knowledge of this or that."
Socrates: Moreover, he might answer shortly and simply, but he makes an enormous circuit. For
example, when asked about the day, he might have said simply, that clay is moistened
earth-what sort of clay is not to the point.
Theaetetus: Yes, Socrates, there is no difficulty as you put the question. You mean, if I am not
mistaken, something like what occurred to me and to my friend here, your namesake
Socrates, in a recent discussion.
Socrates: What was that, Theaetetus?
Theaetetus: Theodorus was writing out for us something about roots, such as the roots of three
or five, showing that they are incommensurable by the unit: he selected other examples up to
seventeen-there he stopped. Now as there are innumerable roots, the notion occurred to us
of attempting to include them all under one name or class.
Socrates: And did you find such a class?
Theaetetus: I think that we did; but I should like to have your opinion.
Socrates: Let me hear.
Theaetetus: We divided all numbers into two classes: those which are made up of equal factors
multiplying into one another, which we compared to square figures and called square or
equilateral numbers;-that was one class.
Socrates: Very good.
Theaetetus: The intermediate numbers, such as three and five, and every other number which is
made up of unequal factors, either of a greater multiplied by a less, or of a less multiplied by a
greater, and when regarded as a figure, is contained in unequal sides;-all these we compared
to oblong figures, and called them oblong numbers.
Socrates: Capital; and what followed?
Theaetetus: The lines, or sides, which have for their squares the equilateral plane numbers, were
called by us lengths or magnitudes; and the lines which are the roots of (or whose squares are
equal to) the oblong numbers, were called powers or roots; the reason of this latter name
being, that they are commensurable with the former
i.e., with the so-called lengths or magnitudes not in linearmeasurement, but in the value of
the superficial content of their squares; and the same about solids.
Socrates: Excellent, my boys; I think that you fully justify the praises of Theodorus, and that he
will not be found guilty of false witness.
Theaetetus: But I am unable, Socrates, to give you a similar answer about knowledge, which is
what you appear to want; and therefore Theodorus is a deceiver after all.
Socrates: Well, but if some one were to praise you for running, and to say that he never met your
equal among boys, and afterwards you were beaten in a race by a grown-up man, who was
a great runner-would the praise be any the less true?
Theaetetus: Certainly not.
Socrates: And is the discovery of the nature of knowledge so small a matter, as just now said? Is
it not one which would task the powers of men perfect in every way?
Theaetetus: By heaven, they should be the top of all perfection!
Socrates: Well, then, be of good cheer; do not say that Theodorus was mistaken about you, but
do your best to ascertain the true nature of knowledge, as well as of other things.
Theaetetus: I am eager enough, Socrates, if that would bring to light the truth.
Socrates: Come, you made a good beginning just now; let your own answer about roots be your
model, and as you comprehended them all in one class, try and bring the many sorts of
knowledge under one definition.
Theaetetus: I can assure you, Socrates, that I have tried very often, when the report of questions
asked by you was brought to me; but I can neither persuade myself that I have a satisfactory
answer to give, nor hear of any one who answers as you would have him; and I cannot shake
off a feeling of anxiety.
Socrates: These are the pangs of labour, my dear Theaetetus; you have something within you
which you are bringing to the birth.
Theaetetus: I do not know, Socrates; I only say what I feel.
Socrates: And have you never heard, simpleton, that I am the son of a midwife, brave and burly,
whose name was Phaenarete?
Why does Socrates call himself a midwife?
Theaetetus: Yes, I have.
Socrates: And that I myself practise midwifery?
Theaetetus: No, never.
Socrates: Let me tell you that I do though, my friend: but you must not reveal the secret, as the
world in general have not found me out; and therefore they only say of me, that I am the
strangest of mortals and drive men to their wits' end. Did you ever hear that too?
Socrates: Shall I tell you the reason?
Theaetetus: By all means.
Socrates: Bear in mind the whole business of the mid-wives, and then you will see my meaning
better:-No woman, as you are probably aware, who is still able to conceive and bear,
attends other women, but only those who are past bearing.
Theaetetus: Yes; I know.
Socrates: The reason of this is said to be that Artemis-the goddess of childbirth-is not a mother,
and she honours those who are like herself; but she could not allow the barren to be
mid-wives, because human nature cannot know the mystery of an art without experience; and
therefore she assigned this office to those who are too old to bear.
Theaetetus: I dare say.
Socrates: And I dare say too, or rather I am absolutely certain, that the mid-wives know better
than others who is pregnant and who is not?
Theaetetus: Very true.
Socrates: And by the use of potions and incantations they are able to arouse the pangs and to
soothe them at will; they can make those bear who have a difficulty in bearing, and if they
think fit they can smother the embryo in the womb.
Theaetetus: They can.
Socrates: Did you ever remark that they are also most cunning matchmakers, and have a thorough
knowledge of what unions are likely to produce a brave brood?
Theaetetus: No, never.
Socrates: Then let me tell you that this is their greaquiz pride, more than cutting the umbilical cord.
And if you reflect, you will see that the same art which cultivates and gathers in the fruits of
the earth, will be most likely to know in what soils the several plants or seeds should be
Theaetetus: Yes, the same art.
Socrates: And do you suppose that with women the case is otherwise?
Theaetetus: I should think not.
Socrates: Certainly not; but mid-wives are respectable women who have a character to lose, and
they avoid this department of their profession, because they are afraid of being called
procuresses, which is a name given to those who join together man and woman in an unlawful
and unscientific way; and yet the true midwife is also the true and only matchmaker.
Socrates: Such are the mid-wives, whose task is a very important one but not so important as
mine; for women do not bring into the world at one time real children, and at another time
counterfeits which are with difficulty distinguished from them; if they did, then the,
discernment of the true and false birth would be the crowning achievement of the art of
midwifery-you would think so?
Theaetetus: Indeed I should.
Socrates: Well, my art of midwifery is in most respects like theirs; but differs, in that I attend men
and not women; and look after their souls when they are in labour, and not after their bodies:
and the triumph of my art is in thoroughly examining whether the thought which the mind of
the young man brings forth is a false idol or a noble and true birth. And like the mid-wives, I
am barren, and the reproach which is often made against me, that I ask questions of others
and have not the wit to answer them myself, is very just-the reason is, that the god
compels-me to be a midwife, but does not allow me to bring forth. And therefore I am not
myself at all wise, nor have I anything to show which is the invention or birth of my own soul,
but those who converse with me profit. Some of them appear dull enough at first, but
afterwards, as our acquaintance ripens, if the god is gracious to them, they all make
astonishing progress; and this in the opinion of others as well as in their own. It is quite dear
that they never learned anything from me; the many fine discoveries to which they cling are of
their own making. But to me and the god they owe their delivery. And the proof of my words
is, that many of them in their ignorance, either in their self-conceit despising me, or falling
under the influence of others, have gone away too soon; and have not only lost the children of
whom I had previously delivered them by an ill bringing up, but have stifled whatever else
they had in them by evil communications, being fonder of lies and shams than of the truth; and
they have at last ended by seeing themselves, as others see them, to be great fools.
Aristeides, the son of Lysimachus, is one of them, and there are many others. The truants
often return to me, and beg that I would consort with them again-they are ready to go to me
on their knees and then, if my familiar allows, which is not always the case, I receive them,
and they begin to grow again. Dire are the pangs which my art is able to arouse and to allay
in those who consort with me, just like the pangs of women in childbirth; night and day they
are full of perplexity and travail which is even worse than that of the women. So much for
them. And there are -others, Theaetetus, who come to me apparently having nothing in them;
and as I know that they have no need of my art, I coax them into marrying some one, and by
the grace of God I can generally tell who is likely to do them good. Many of them I have
given away to Prodicus, and many to other inspired sages. I tell you this long story, friend
Theaetetus, because I suspect, as indeed you seem to think yourself, that you are in
labour-great with some conception. Come then to me, who am a midwife's son and myself a
midwife, and do your best to answer the questions which I will ask you. And if I abstract and
expose your first-born, because I discover upon inspection that the conception which you
have formed is a vain shadow, do not quarrel with me on that account, as the manner of
women is when their first children are taken from them. For I have actually known some who
were ready to bite me when I deprived them of a darling folly; they did not perceive that I
acted from good will, not knowing that no god is the enemy of man-that was not within the
range of their ideas; neither am I their enemy in all this, but it would be wrong for me to admit
falsehood, or to stifle the truth. Once more, then, Theaetetus, I repeat my old question,
"What is knowledge?"-and do not say that you cannot tell; but quit yourself like a man, and
by the help of God you will be able to tell.
Why does Socrates refer to himself as "barren?"
Theaetetus: At any rate, Socrates, after such an exhortation I should be ashamed of not trying to
do my best. Now he who knows perceives what he knows, and, as far as I can see at
present, knowledge is perception.
Socrates: Bravely said, boy; that is the way in which you should express your opinion. And now,
let us examine together this conception of yours, and see whether it is a true birth or a mere,
wind-egg:-You say that knowledge is perception?
Is Theaetetus theory that "knowledge is perception" at all plausible?
Socrates: Well, you have delivered yourself of a very important doctrine about knowledge; it is
indeed the opinion of Protagoras, who has another way of expressing it, Man, he says, is the
measure of all things, of the existence of things that are, and of the non-existence of things that
are not:-You have read him?
Theaetetus: O yes, again and again.
Socrates: Does he not say that things are to you such as they appear to you, and to me such as
they appear to me, and that you and I are men?
Theaetetus: Yes, he says so.
Socrates: A wise man is not likely to talk nonsense. Let us try to understand him: the same wind is
blowing, and yet one of us may be cold and the other not, or one may be slightly and the
other very cold?
Theaetetus: Quite true.
Socrates: Now is the wind, regarded not in relation to us but absolutely, cold or not; or are we to
say, with Protagoras, that the wind is cold to him who is cold, and not to him who is not?
Theaetetus: I suppose the last.
Socrates: Then it must appear so to each of them?
Socrates: And "appears to him" means the same as "he perceives."
Socrates: Then appearing and perceiving coincide in the case of hot and cold, and in similar
instances; for things appear, or may be supposed to be, to each one such as he perceives
Socrates: Then perception is always of existence, and being the same as knowledge is unerring?
Socrates: In the name of the Graces, what an almighty wise man Protagoras must have been! He
spoke these things in a parable to the common herd, like you and me, but told the truth, his
Truth, in secret to his own disciples.
Theaetetus: What do you mean, Socrates?
Socrates: I am about to speak of a high argument, in which all things are said to be relative; you
cannot rightly call anything by any name, such as great or small, heavy or light, for the great
will be small and the heavy light-there is no single thing or quality, but out of motion and
change and admixture all things are becoming relatively to one another, which "becoming" is
by us incorrectly called being, but is really becoming, for nothing ever is, but all things are
becoming. Summon all philosophers-Protagoras, Heracleitus, Empedocles, and the rest of
them, one after another, and with the exception of Parmenides they will agree with you in this.
Summon the great masters of either kind of poetry-Epicharmus, the prince of Comedy, and
Homer of Tragedy; when the latter sings of
Ocean whence sprang the gods, and mother Tethys, does he not mean that all things are the
offspring, of flux and motion?
Theaetetus: I think so.
Socrates: And who could take up arms against such a great army having Homer for its general,
and not appear ridiculous?
Theaetetus: Who indeed, Socrates?
Socrates: Yes, Theaetetus; and there are plenty of other proofs which will show that motion is the
source of what is called being and becoming, and inactivity of not-being and destruction; for
fire and warmth, which are supposed to be the parent and guardian of all other things, are
born of movement and friction, which is a kind of motion;-is not this the origin of fire?
Theaetetus: It is.
Socrates: And the race of animals is generated in the same way?
Socrates: And is not the bodily habit spoiled by rest and idleness, but preserved for a long time by
motion and exercise?
Socrates: And what of the mental habit? Is not the soul informed, and improved, and preserved
by study and attention, which are motions; but when at rest, which in the soul only means
want of attention and study, is uninformed, and speedily forgets whatever she has learned?
Socrates: Then motion is a good, and rest an evil, to the soul as well as to the body?
Socrates: I may add, that breathless calm, stillness and the like waste and impair, while wind and
storm preserve; and the palmary argument of all, which I strongly urge, is the golden chain in
Homer, by which he means the sun, thereby indicating that so long as the sun and the heavens
go round in their orbits, all things human and divine are and are preserved, but if they were
chained up and their motions ceased, then all things would be destroyed, and, as the saying
is, turned upside down.
Theaetetus: I believe, Socrates, that you have truly explained his meaning.
Socrates: Then now apply his doctrine to perception, my good friend, and first of all to vision; that
which you call white colour is not in your eyes, and is not a distinct thing which exists out of
them. And you must not assign any place to it: for if it had position it would be, and be at rest,
and there would be no process of becoming.
Theaetetus: Then what is colour?
Socrates: Let us carry the principle which has just been affirmed, that nothing is self-existent, and
then we shall see that white, black, and every other colour, arises out of the eye meeting the
appropriate motion, and that what we call a colour is in each case neither the active nor the
passive element, but something which passes between them, and is peculiar to each
percipient; are you quite certain that the several colours appear to a dog or to any animal
whatever as they appear to you?
Theaetetus: Far from it.
Socrates: Or that anything appears the same to you as to another man? Are you so profoundly
convinced of this? Rather would it not be true that it never appears exactly the same to you,
because you are never exactly the same?
Theaetetus: The latter.
Socrates: And if that with which I compare myself in size, or which I apprehend by touch, were
great or white or hot, it could not become different by mere contact with another unless it
actually changed; nor again, if the comparing or apprehending subject were great or white or
hot, could this, when unchanged from within become changed by any approximation or
affection of any other thing. The fact is that in our ordinary way of speaking we allow
ourselves to be driven into most ridiculous and wonderful contradictions, as Protagoras and
all who take his line of argument would remark.
Theaetetus: How? and of what sort do you mean?
Socrates: A little instance will sufficiently explain my meaning: Here are six dice, which are more
by a half when compared with four, and fewer by a half than twelve-they are more and also
fewer. How can you or any one maintain the contrary?
Theaetetus: Very true.
Socrates: Well, then, suppose that Protagoras or some one asks whether anything can become
greater or more if not by increasing, how would you answer him, Theaetetus?
Theaetetus: I should say "No," Socrates, if I were to speak my mind in reference to this last
question, and if I were not afraid of contradicting my former answer.
Socrates: Capital excellent! spoken like an oracle, my boy! And if you reply "Yes," there will be a
case for Euripides; for our tongue will be unconvinced, but not our mind.
Theaetetus: Very true.
Socrates: The thoroughbred Sophists, who know all that can be known about the mind, and argue
only out of the superfluity of their wits, would have had a regular sparring-match over this,
and would -have knocked their arguments together finely. But you and I, who have no
professional aims, only desire to see what is the mutual relation of these principles-whether
they are consistent with each or not.
Theaetetus: Yes, that would be my desire.
Socrates: And mine too. But since this is our feeling, and there is plenty of time, why should we
not calmly and patiently review our own thoughts, and thoroughly examine and see what
these appearances in us really are? If I am not mistaken, they will be described by us as
follows:-first, that nothing can become greater or less, either in number or magnitude, while
remaining equal to itself-you would agree?
Socrates: Secondly, that without addition or subtraction there is no increase or diminution of
anything, but only equality.
Theaetetus: Quite true.
Socrates: Thirdly, that what was not before cannot be afterwards, without becoming and having
Theaetetus: Yes, truly.
Socrates: These three axioms, if I am not mistaken, are fighting with one another in our minds in
the case of the dice, or, again, in such a case as this-if I were to say that I, who am of a
certain height and taller than you, may within a year, without gaining or losing in height, be not
so tall-not that I should have lost, but that you would have increased. In such a case, I am
afterwards what I once was not, and yet I have not become; for I could not have become
without becoming, neither could I have become less without losing somewhat of my height;
and I could give you ten thousand examples of similar contradictions, if we admit them at all. I
believe that you follow me, Theaetetus; for I suspect that you have thought of these questions
Theaetetus: Yes, Socrates, and I am amazed when I think of them; by the Gods I am! and I
want to know what on earth they mean; and there are times when my head quite swims with
the contemplation of them.
Socrates: I see, my dear Theaetetus, that Theodorus had a true insight into your nature when he
said that you were a philosopher, for wonder is the feeling of a philosopher, and philosophy
begins in wonder. He was not a bad genealogist who said that Iris (the messenger of heaven)
is the child of Thaumas (wonder). But do you begin to see what is the explanation of this
perplexity on the hypothesis which we attribute to Protagoras?
Theaetetus: Not as yet.
Socrates: Then you will be obliged to me if I help you to unearth the hidden "truth" of a famous
man or school.
Theaetetus: To be sure, I shall be very much obliged.
Socrates: Take a look round, then, and see that none of the uninitiated are listening. Now by the
uninitiated I mean: the people who believe in nothing but what they can grasp in their hands,
and who will not allow that action or generation or anything invisible can have real existence.
Theaetetus: Yes, indeed, Socrates, they are very hard and impenetrable mortals.
Socrates: Yes, my boy, outer barbarians. Far more ingenious are the brethren whose mysteries I
am about to reveal to you. Their first principle is, that all is motion, and upon this all the
affections of which we were just now speaking, are supposed to depend: there is nothing but
motion, which has two forms, one active and the other passive, both in endless number; and
out of the union and friction of them there is generated a progeny endless in number, having
two forms, sense and the object of sense, which are ever breaking forth and coming to the
birth at the same moment. The senses are variously named hearing, seeing, smelling; there is
the sense of heat, cold, pleasure, pain, desire, fear, and many more which have names, as
well as innumerable others which are without them; each has its kindred object each variety
of colour has a corresponding variety of sight, and so with sound and hearing, and with the
rest of the senses and the objects akin to them. Do you see, Theaetetus, the bearings of this
tale on the preceding argument?
Theaetetus: Indeed I do not.
Socrates: Then attend, and I will try to finish the story. The purport is that all these things are in
motion, as I was saying, and that this motion is of two kinds, a slower and a quicker; and the
slower elements have their motions in the same place and with reference to things near them,
and so they beget; but what is begotten is swifter, for it is carried to fro, and moves from
place to place. Apply this to sense:-When the eye and the appropriate object meet together
and give birth to whiteness and the sensation connatural with it, which could not have been
given by either of them going elsewhere, then, while the sight: is flowing from the eye,
whiteness proceeds from the object which combines in producing the colour; and so the eye
is fulfilled with sight, and really sees, and becomes, not sight, but a seeing eye; and the object
which combined to form the colour is fulfilled with whiteness, and becomes not whiteness but
a white thing, whether wood or stone or whatever the object may be which happens to be
colour,ed white. And this is true of all sensible objects, hard, warm, and the like, which are
similarly to be regarded, as I was saying before, not as having any absolute existence, but as
being all of them of whatever kind. generated by motion in their intercourse with one another;
for of the agent and patient, as existing in separation, no trustworthy conception, as they say,
can be formed, for the agent has no existence until united; with the patient, and the patient has
no existence until united with the agent; and that which by uniting with something becomes an
agent, by meeting with some other thing is converted into a patient. And from all these
considerations, as I said at first, there arises a general reflection, that there is no one
self-existent thing, but everything is becoming and in relation; and being must be altogether
abolished, although from habit and ignorance we are compelled even in this discussion to
retain the use of the term. But great philosophers tell us that we are not to allow either the
word "something," or "belonging to something," or "to me," or "this," or "that," or any other
detaining name to be used, in the language of nature all things are being created and
destroyed, coming into being and passing into new forms; nor can any name fix or detain
them; he who attempts to fix them is easily refuted. And this should be the way of speaking,
not only of particulars but of aggregates such aggregates as are expressed in the word "man,"
or "stone," or any name of animal or of a class. O Theaetetus, are not these speculations
sweet as honey? And do you not like the taste of them in the mouth?
Explain Socrates thinks that they eye can see.
How does this understanding of sense relations lead to the position that " there is no one self-existent thing, but everything is becoming and in relation"
Theaetetus: I do not know what to say, Socrates, for, indeed, I cannot make out whether you
are giving your own opinion or only wanting to draw me out.
Socrates: You forget, my friend, that I neither know, nor profess to know, anything of! these
matters; you are the person who is in labour, I am the barren midwife; and this is why I
soothe you, and offer you one good thing after another, that you may taste them. And I hope
that I may at last help to bring your own opinion into the light of day: when this has been
accomplished, then we will determine whether what you have brought forth is only a
wind-egg or a real and genuine birth. Therefore, keep up your spirits, and answer like a man
what you think.
Theaetetus: Ask me.
Socrates: Then once more: Is it your opinion that nothing is but what becomes? the good and the
noble, as well; as all the other things which we were just now mentioning?
Theaetetus: When I hear you discoursing in this style, I think that there is a great deal in what
you say, and I am very ready to assent. Socrates: Let us not leave the argument unfinished, then;
for there still remains to be considered an objection which may be raised about dreams and
diseases, in particular about madness, and the various illusions of hearing and sight, or of
other senses. For you know that in all these cases the esse-percipi theory appears to be
unmistakably refuted, since in dreams and illusions we certainly have false perceptions; and
far from saying that everything is which appears, we should rather say that nothing is which
Why is it important to consider the case of dreams and madness?
Theaetetus: Very true, Socrates.
Socrates: But then, my boy, how can any one contend that knowledge is perception, or that to
every man what appears is?
Theaetetus: I am afraid to say, Socrates, that I have nothing to answer, because you rebuked
me just now for making this excuse; but I certainly cannot undertake to argue that madmen or
dreamers think truly, when they imagine, some of them that they are gods, and others that
they can fly, and are flying in their sleep.
Socrates: Do you see another question which can be raised about these phenomena, notably
about dreaming and waking?
Theaetetus: What question?
Socrates: A question which I think that you must often have heard persons ask:-How can you
determine whether at this moment we are sleeping, and all our thoughts are a dream; or
whether we are awake, and talking to one another in the waking state?
Theaetetus: Indeed, Socrates, I do not know how to prove the one any more than the other, for
in both cases the facts precisely correspond;-and there is no difficulty in supposing that during
all this discussion we have been talking to one another in a dream; and when in a dream we
seem to be narrating dreams, the resemblance of the two states is quite astonishing.
Why is it that Theaetetus cannot assert that as he speaks to Socrates he is not in fact dreaming?
Socrates: You see, then, that a doubt about the reality of sense is easily raised, since there may
even be a doubt whether we are awake or in a dream. And as our time is equally divided
between sleeping and waking, in either sphere of existence the soul contends that the thoughts
which are present to our minds at the time are true; and during one half of our lives we affirm
the truth of the one, and, during the other half, of the other; and are equally confident of both.
Theaetetus: Most true.
Socrates: And may not the same be said of madness and other disorders? the difference is only
that the times are not equal.
Socrates: And is truth or falsehood to be determined by duration of time?
Theaetetus: That would be in many ways ridiculous.
Socrates: But can you certainly determine: by any other means which of these opinions is true?
Theaetetus: I do not think that I can.
Socrates: Listen, then to a statement of the other side of the argument, which is made by the
champions of appearance. They would say, as I imagine-can that which is wholly other than
something, have the same quality as that from which it differs? and observe, -Theaetetus, that
the word "other" means not "partially," but "wholly other."
Theaetetus: Certainly, putting the question as you do, that which is wholly other cannot either
potentially or in any other way be the same.
Socrates: And must therefore be admitted to be unlike?
Socrates: If, then, anything happens to become like or unlike itself or another, when it becomes
like we call it the same-when unlike, other?
Socrates: Were we not saying that there. are agents many and infinite, and patients many and
Socrates: And also that different combinations will produce results which are not the same, but
Socrates: Let us take you and me, or anything as an example:-There is Socrates in health, and
Socrates sick-Are they like or unlike?
Theaetetus: You mean to, compare Socrates in health as a whole, and Socrates in sickness as a
Socrates: Exactly; that is my meaning.
Theaetetus: I answer, they are unlike.
Socrates: And if unlike, they are other?
Socrates: And would you not say the same of Socrates sleeping and waking, or in any of the
states which we were mentioning?
Theaetetus: I should.
Socrates: All agents have a different patient in Socrates, accordingly as he is well or ill.
Theaetetus: Of course.
Socrates: And I who am the patient, and that which is the agent, will produce something different
in each of the two cases?
Socrates: The wine which I drink when I am in health, appears sweet and pleasant to me?
Socrates: For, as has been already acknowledged, the patient and agent meet together and
produce sweetness and a perception of sweetness, which are in simultaneous motion, and the
perception which comes from the patient makes the tongue percipient, and the quality of
sweetness which arises out of and is moving about the wine, makes the wine, both to be and
to appear sweet to the healthy tongue.
Theaetetus: Certainly; that has been already acknowledged.
Socrates: But when I am sick, the wine really acts upon another and a different person?
Socrates: The combination of the draught of wine, and the Socrates who is sick, produces quite
another result; which is the sensation of bitterness in the tongue, and the, motion and creation
of bitterness in and about the wine, which becomes not bitterness but something bitter; as I
myself become not but percipient?
Socrates: There is no, other object of which I shall ever have the same perception, for another
object would give another perception, and would make the perception other and different;
nor can that object which affects me, meeting another, subject, produce, the same, or
become similar, for that too would produce another result from another subject, and become
Socrates: Neither can by myself, have this sensation, nor the object by itself, this quality.
Theaetetus: Certainly not.
Socrates: When I perceive I must become percipient of something-there can be no such thing as
perceiving and perceiving nothing; the object, whether it become sweet, bitter, or of any
other quality, must have relation to a percipient; nothing can become sweet which is sweet to
Explain "When I perceive I must become percipient of something"
Theaetetus: Certainly not.
Socrates: Then the inference is, that we [the agent and patient] are or become in relation to one
another; there is a law which binds us one to the other, but not to any other existence, nor
each of us to himself; and therefore we can only be bound to one another; so that whether a
person says that a thing is or becomes, he must say that it is or becomes to or of or in relation
to something else; but he must not say or allow any one else to say that anything is or
becomes absolutely: -such is our conclusion.
Theaetetus: Very true, Socrates.
Socrates: Then, if that which acts upon me has relation to me and to no other, I and no other am
the percipient of it?
Theaetetus: Of course.
Socrates: Then my perception is true to me, being inseparable from my own being; and, as
Protagoras says, to myself I am judge of what is and-what is not to me.
Theaetetus: I suppose so.
Socrates: How then, if I never err, and if my mind never trips in the conception of being or
becoming, can I fail of knowing that which I perceive?
Theaetetus: You cannot.
Socrates: Then you were quite right in affirming that knowledge is only perception; and the
meaning turns out to be the same, whether with Homer and Heracleitus, and all that
company, you say that all is motion and flux, or with the great sage Protagoras, that man is
the measure of all things; or with Theaetetus, that, given these premises, perception is
knowledge. Am I not right, Theaetetus, and is not this your newborn child, of which I have
delivered you? What say you?
Theaetetus: I cannot but agree, Socrates.
Socrates: Then this is the child, however he may turn out, which you and I have with difficulty
brought into the world. And now that he is born, we must run round the hearth with him, and
see whether he is worth rearing, or is only a wind-egg and a sham. Is he to be reared in any
case, and not exposed? or will you bear to see him rejected, and not get into a passion if I
take away your first-born?
Theodorus: Theaetetus will not be angry, for he is very good-natured. But tell me, Socrates, in
heaven's name, is this, after all, not the truth?
Socrates: You, Theodorus, are a lover of theories, and now you innocently fancy that I am a bag
full of them, and can easily pull one out which will overthrow its predecessor. But you do not
see that in reality none of these theories come from me; they all come from him who talks
with me. I only know just enough to extract them from the wisdom of another, and to receive
them in a spirit of fairness. And now I shall say nothing myself, but shall endeavour to elicit
something from our young friend.
Theodorus: Do as you say, Socrates; you are quite right.
Socrates: Shall I tell you, Theodorus, what amazes me in your acquaintance Protagoras?
Theodorus: What is it?
Socrates: I am charmed with his doctrine, that what appears is to each one, but I wonder that he
did not begin his book on Truth with a declaration that a pig or a dog-faced baboon, or some
other yet stranger monster which has sensation, is the measure of all things; then he might
have shown a magnificent contempt for our opinion of him by informing us at the outset that
while we were reverencing him like a God for his wisdom he was no better than a tadpole,
not to speak of his fellow-men-would not this have produced an over-powering effect? For if
truth is only sensation, and no man can discern another's feelings better than he, or has any
superior right to determine whether his opinion is true or false, but each, as we have several
times repeated, is to himself the sole judge, and everything that he judges is true and right,
why, my friend, should Protagoras be preferred to the place of wisdom and instruction, and
deserve to be well paid, and we poor ignoramuses have to go to him, if each one is the
measure of his own wisdom? Must he not be talking ad captandum in all this? I say nothing of
the ridiculous predicament in which my own midwifery and the whole art of dialectic is
placed; for the attempt to supervise or refute the notions or opinions of others would be a
tedious and enormous piece of folly, if to each man his own are right; and this must be the
case if Protagoras Truth is the real truth, and the philosopher is not merely amusing himself by
giving oracles out of the shrine of his book.
Theodorus: He was a friend of mine, Socrates, as you were saying, and therefore I cannot have
him refuted by my lips, nor can I oppose you when I agree with you; please, then, to take
Theaetetus again; he seemed to answer very nicely.
Socrates: If you were to go into a Lacedaemonian palestra, Theodorus, would you have a right to
look on at the naked wrestlers, some of them making a poor figure, if you did not strip and
give them an opportunity of judging of your own person?
Theodorus: Why not, Socrates, if they would allow me, as I think you will in consideration of my
age and stiffness; let some more supple youth try a fall with you, and do not drag me into the
Socrates: Your will is my will, Theodorus, as the proverbial philosophers say, and therefore I will
return to the sage Theaetetus: Tell me, Theaetetus, in reference to what I was saying, are you
not lost in wonder, like myself, when you find that all of a sudden you are raised to the level
of the wisest of men, or indeed of the gods?-for you would assume the measure of
Protagoras to apply to the gods as well as men?
Theaetetus: Certainly I should, and I confess to you that I am lost in wonder. At first hearing, I
was quite satisfied with the doctrine, that whatever appears is to each one, but now the face
of things has changed.
Socrates: Why, my dear boy, you are young, and therefore your ear is quickly caught and your
mind influenced by popular arguments. Protagoras, or some one speaking on his behalf, will
doubtless say in reply, good people, young and old, you meet and harangue, and bring in the
gods, whose existence of non-existence I banish from writing and speech, or you talk about
the reason of man being degraded to the level of the brutes, which is a telling argument with
the multitude, but not one word of proof or demonstration do you offer. All is probability with
you, and yet surely you and Theodorus had better reflect whether you are disposed to admit
of probability and figures of speech in matters of such importance. He or any other
mathematician who argued from probabilities and likelihoods in geometry, would not be
worth an ace.
Theaetetus: But neither you nor we, Socrates, would be satisfied with such arguments.
Socrates: Then you and Theodorus mean to say that we must look at the matter in some other
Theaetetus: Yes, in quite another way.
Socrates: And the way will be to ask whether perception is or is not the same as knowledge; for
this was the real point of our argument, and with a view to this we raised (did we not?) those
many strange questions.
Socrates: Shall we say that we know every thing which we see and hear? for example, shall we
say that not having learned, we do not hear the language of foreigners when they speak to us?
or shall we say that we not only hear, but know what they are saying? Or again, if we see
letters which we do not understand, shall we say that we do not see them? or shall we aver
that, seeing them, we must know them?
Theaetetus: We shall say, Socrates, that we know what we actually see and hear of them-that is
to say, we see and know the figure and colour of the letters, and we hear and know the
elevation or depression of the sound of them; but we do not perceive by sight and hearing, or
know, that which grammarians and interpreters teach about them.
Socrates: Capital, Theaetetus; and about this there shall be no dispute, because I want you to
grow; but there is another difficulty coming, which you will also have to repulse.
Theaetetus: What is it?
Socrates: Some one will say, Can a man who has ever known anything, and still has and
preserves a memory of that which he knows, not know that which he remembers at the time
when he remembers? I have, I fear, a tedious way of putting a simple question, which is only,
whether a man who has learned, and remembers, can fail to know?
Theaetetus: Impossible, Socrates; the supposition is monstrous.
Socrates: Am I talking nonsense, then? Think: is not seeing perceiving, and is not sight perception?
Socrates: And if our recent definition holds, every man knows that which he has seen?
Socrates: And you would admit that there is such a thing as memory?
Socrates: And is memory of something or of nothing?
Theaetetus: Of something, surely.
Socrates: Of things learned and perceived, that is?
Socrates: Often a man remembers that which he has seen?
Socrates: And if he closed his eyes, would he forget?
Theaetetus: Who, Socrates, would dare to say so?
Socrates: But we must say so, if the previous argument is to be maintained.
Theaetetus: What do you mean? I am not quite sure that I understand you, though I have a
strong suspicion that you are right.
Socrates: As thus: he who sees knows, as we say, that which he sees; for perception and sight
and knowledge are admitted to be the same.
Socrates: But he who saw, and has knowledge of that which he saw, remembers, when he closes
his eyes, that which he no longer sees.
Socrates: And seeing is knowing, and therefore not-seeing is not-knowing?
Theaetetus: Very true.
Socrates: Then the inference is, that a man may have attained the knowledge, of something, which
he may remember and yet not know, because he does not see; and this has been affirmed by
us to be a monstrous supposition.
Theaetetus: Most true.
Socrates: Thus, then, the assertion that knowledge and perception are one, involves a manifest
What is the "manifest impossibility" involved in the assertion that "knowledge and perception are one" given our use of memory?
Socrates: Then they must be distinguished?
Theaetetus: I suppose that they must.
Socrates: Once more we shall have to begin, and ask "What is knowledge?" and yet, Theaetetus,
what are we going to do?
Theaetetus: About what?
Socrates: Like a good-for-nothing cock, without having won the victory, we walk away from the
argument and crow.
Theaetetus: How do you mean?
Socrates: After the manner of disputers, we were satisfied with mere verbal consistency, and were
well pleased if in this way we could gain an advantage. Although professing not to be mere
Eristics, but philosophers, I suspect that we have unconsciously fallen into the error of that
ingenious class of persons.
Theaetetus: I do not as yet understand you.
Socrates: Then I will try to explain myself: just now we asked the question, whether a man who
had learned and remembered could fail to know, and we showed that a person who had seen
might remember when he had his eyes shut and could not see, and then he would at the same
time remember and not know. But this was an impossibility. And so the Protagorean fable
came to nought, and yours also, who maintained that knowledge is the same as perception.
Socrates: And yet, my friend, I rather suspect that the result would have been different if
Protagoras, who was the father of the first of the two-brats, had been alive; he would have
had a great deal to say on their behalf. But he is dead, and we insult over his orphan child;
and even the guardians whom he left, and of whom our friend Theodorus is one, are unwilling
to give any help, and therefore I suppose that must take up his cause myself, and see justice
Theodorus: Not I, Socrates, but rather Callias, the son of Hipponicus, is guardian of his orphans.
I was too soon diverted from the abstractions of dialectic to geometry. Nevertheless, I shall
be grateful to you if you assist him.
Socrates: Very good, Theodorus; you shall see how I will come to the rescue. If a person does
not attend to the meaning of terms as they are commonly used in argument, he may be
involved even in greater paradoxes than these. Shall I explain this matter to you or to
Theodorus: To both of us, and let the younger answer; he will incur less disgrace if he is
Socrates: Then now let me ask the awful question, which is this:-Can a man know and also not
know that which he knows?
Theodorus: How shall we answer, Theaetetus?
Theaetetus: He cannot, I should say.
Socrates: He can, if you maintain that seeing is knowing. When you are imprisoned in a well, as
the saying is, and the self-assured adversary closes one of your eyes with his hand, and asks
whether you can see his cloak with the eye which he has closed, how will you answer the
Theaetetus: I should answer, "Not with that eye but with the other."
Socrates: Then you see and do not see the same thing at the same time.
Theaetetus: Yes, in a certain sense.
Socrates: None of that, he will reply; I do not ask or bid you answer in what sense you know, but
only whether you know that which you do not know. You have been proved to see that
which you do not see; and you have already admitted that seeing is knowing, and that
not-seeing is not-knowing: I leave you to draw the inference.
Theaetetus: Yes, the inference is the contradictory of my assertion.
Explain how Socrates proves you can know and not know at the same time.
Socrates: Yes, my marvel, and there might have been yet worse things in store for you, if an
opponent had gone on to ask whether you can have a sharp and also a dull knowledge, and
whether you can know near, but not at a distance, or know the same thing with more or less
intensity, and so on without end. Such questions might have been put to you by a light-armed
mercenary, who argued for pay. He would have lain in wait for you, and when you took up
the position, that sense is knowledge, he would have made an assault upon hearing, smelling,
and the other senses;-he would have shown you no mercy; and while you were lost in envy
and admiration of his wisdom, he would have got you into his net, out of which you would not
have escaped until you had come to an understanding about the sum to be paid for your
release. Well, you ask, and how will Protagoras reinforce his position? Shall I answer for
Theaetetus: By all means.
Socrates: He will repeat all those things which we have been urging on his behalf, and then he will
close with us in disdain, and say:-The worthy Socrates asked a little boy, whether the same
man could remember and not know the same thing, and the boy said No, because he was
frightened, and could not see what was coming, and then Socrates made fun of poor me. The
truth is, O slatternly Socrates, that when you ask questions about any assertion of mine, and
the person asked is found tripping, if he has answered as I should have answered, then I am
refuted, but if he answers something else, then he is refuted and not I. For do you really
suppose that any one would admit the memory which a man has of an impression which has
passed away to be the same with that which he experienced at the time? Assuredly not. Or
would he hesitate to acknowledge that the same man may know and not know the same
thing? Or, if he is afraid of making this admission, would he ever grant that one who has
become unlike is the same as before he became unlike? Or would he admit that a man is one
at all, and not rather many and infinite as the changes which take place in him? I speak by the
card in order to avoid entanglements of words. But, O my good sir, he would say, come to
the argument in a more generous spirit; and either show, if you can, that our sensations are
not relative and individual, or, if you admit them to be so, prove that this does not involve the
consequence that the appearance becomes, or, if you will have the word, is, to the individual
only. As to your talk about pigs and baboons, you are yourself behaving like a pig, and you
teach your hearers to make sport of my writings in the same ignorant manner; but this is not
to your credit. For I declare that the truth is as I have written, and that each of us is a
measure of existence and of non-existence. Yet one man may be a thousand times better than
another in proportion as different things are and appear to him.
And I am far from saying that wisdom and the wise man have no existence; but I say that the
wise man is he who makes the evils which appear and are to a man, into goods which are
and appear to him. And I would beg you not to my words in the letter, but to take the
meaning of them as I will explain them. Remember what has been already said,-that to the
sick man his food appears to be and is bitter, and to the man in health the opposite of bitter.
Now I cannot conceive that one of these men can be or ought to be made wiser than the
other: nor can you assert that the sick man because he has one impression is foolish, and the
healthy man because he has another is wise; but the one state requires to be changed into the
other, the worse into the better. As in education, a change of state has to be effected, and the
sophist accomplishes by words the change which the physician works by the aid of drugs.
Not that any one ever made another think truly, who previously thought falsely. For no one
can think what is not, or think anything different from that which he feels; and this is always
true. But as the inferior habit of mind has thoughts of kindred nature, so I conceive that a
good mind causes men to have good thoughts; and these which the inexperienced call true, I
maintain to be only better, and not truer than others. And, O my dear Socrates, I do not call
wise men tadpoles: far from it; I say that they are the physicians of the human body, and the
husbandmen of plants-for the husbandmen also take away the evil and disordered sensations
of plants, and infuse into them good and healthy sensations-aye and true ones; and the wise
and good rhetoricians make the good instead of the evil to seem just to states; for whatever
appears to a state to be just and fair, so long as it is regarded as such, is just and fair to it; but
the teacher of wisdom causes the good to take the place of the evil, both in appearance and
in reality. And in like manner the Sophist who is able to train his pupils in this spirit is a wise
man, and deserves to be well paid by them. And so one man is wiser than another; and no
one thinks falsely, and you, whether you will or not, must endure to be a measure. On these
foundations the argument stands firm, which you, Socrates, may, if you please, overthrow by
an opposite argument, or if you like you may put questions to me-a method to which no
intelligent person will object, quite the reverse. But I must beg you to put fair questions: for
there is great inconsistency in saying that you have a zeal for virtue, and then always behaving
unfairly in argument. The unfairness of which I complain is that you do not distinguish between
mere disputation and dialectic: the disputer may trip up his opponent as often as he likes, and
make fun; but the dialectician will be in earnest, and only correct his adversary when
necessary, telling him the errors into which he has fallen through his own fault, or that of the
company which he has previously kept. If you do so, your adversary will lay the blame of his
own confusion and perplexity on himself, and not on you; will follow and love you, and will
hate himself, and escape from himself into philosophy, in order that he may become different
from what he was. But the other mode of arguing, which is practised by the many, will have
just the opposite effect upon him; and as he grows older, instead of turning philosopher, he
will come to hate philosophy. I would recommend you, therefore, as I said before, not to
encourage yourself in this polemical and controversial temper, but to find out, in a friendly and
congenial spirit, what we really mean when we say that all things are in motion, and that to
every individual and state what appears, is. In this manner you will consider whether
knowledge and sensation are the same or different, but you will not argue, as you were just
now doing, from the customary use of names and words, which the vulgar pervert in all sorts
of ways, causing infinite perplexity to one another. Such, Theodorus, is the very slight help
which I am able to offer to your old friend; had he been living, he would have helped himself
in a far more gloriose style.
Theodorus: You are jesting, Socrates; indeed, your defence of him has been most valorous.
Socrates: Thank you, friend; and I hope that you observed Protagoras bidding us be serious, as
the text, "Man is the measure of all things," was a solemn one; and he reproached us with
making a boy the medium of discourse, and said that the boy's timidity was made to tell
against his argument; he also declared that we made a joke of him.
Theodorus: How could I fail to observe all that, Socrates?
Socrates: Well, and shall we do as he says?
Theodorus: By all means.
Socrates: But if his wishes are to be regarded, you and I must take up the argument, and in all
seriousness, and ask and answer one another, for you see that the rest of us are nothing but
boys. In no other way can we escape the imputation, that in our fresh analysis of his thesis we
are making fun with boys.
Theodorus: Well, but is not Theaetetus better able to follow a philosophical enquiry than a great
many men who have long beards?
Socrates: Yes, Theodorus, but not better than you; and therefore please not to imagine that I am
to defend by every means in my power your departed friend; and that you are to defend
nothing and nobody. At any rate, my good man, do not sheer off until we know whether you
are a true measure of diagrams, or whether all men are equally measures and sufficient for
themselves in astronomy and geometry, and the other branches of knowledge in which you
are supposed to excel them.
Theodorus: He who is sitting by you, Socrates, will not easily avoid being drawn into an
argument; and when I said just now that you would excuse me, and not, like the
Lacedaemonians, compel me to strip and fight, I was talking nonsense-I should rather
compare you to Scirrhon, who threw travellers from the rocks; for the Lacedaemonian rule is
"strip or depart," but you seem to go about your work more after the fashion of Antaeus: you
will not allow any one who approaches you to depart until you have stripped him, and he has
been compelled to try a fall with you in argument.
Socrates: There, Theodorus, you have hit off precisely the nature of my complaint; but I am even
more pugnacious than the giants of old, for I have met with no end of heroes; many a
Heracles, many a Theseus, mighty in words, has broken my head; nevertheless I am always
at this rough exercise, which inspires me like a passion. Please, then, to try a fall with me,
whereby you will do yourself good as well as me.
Theodorus: I consent; lead me whither you will, for I know that you are like destiny; no man can
escape from any argument which you may weave for him. But I am not disposed to go further
than you suggest.
Socrates: Once will be enough; and now take particular care that we do not again unwittingly
expose ourselves to the reproach of talking childishly.
Theodorus: I will do my best to avoid that error.
Socrates: In the first place, let us return to our old objection, and see whether we were right in
blaming and taking offence at Protagoras on the ground that he assumed all to be equal and
sufficient in wisdom; although he admitted that there was a better and worse, and that in
respect of this, some who as he said were the wise excelled others.
Theodorus: Very true.
Socrates: Had Protagoras been living and answered for himself, instead of our answering for him,
there would have been no need of our reviewing or reinforcing the argument. But as he is not
here, and some one may accuse us of speaking without authority on his behalf, had we not
better come to a clearer agreement about his meaning, for a great deal may be at stake?
Socrates: Then let us obtain, not through any third person, but from his own statement and in the
fewest words possible, the basis of agreement.
Theodorus: In what way?
Socrates: In this way:-His words are, "What seems to a man, is to him."
Theodorus: Yes, so he says.
Socrates: And are not we, Protagoras, uttering the opinion of man, or rather of all mankind, when
we say that every one thinks himself wiser than other men in some things, and their inferior in
others? In the hour of danger, when they are in perils of war, or of the sea, or of sickness, do
they not look up to their commanders as if they were gods, and expect salvation from them,
only because they excel them in knowledge? Is not the world full of men in their several
employments, who are looking for teachers and rulers of themselves and of the animals? and
there are plenty who think that they are able to teach and able to rule. Now, in all this is
implied that ignorance and wisdom exist among them, least in their own opinion.
Socrates: And wisdom is assumed by them to be true thought, and ignorance to be false opinion.
Socrates: How then, Protagoras, would you have us treat the argument? Shall we say that the
opinions of men are always true, or sometimes true and sometimes false? In either case, the
result is the same, and their opinions are not always true, but sometimes true and sometimes
false. For tell me, Theodorus, do you suppose that you yourself, or any other follower of
Protagoras, would contend that no one deems another ignorant or mistaken in his opinion?
Theodorus: The thing is incredible, Socrates.
Socrates: And yet that absurdity is necessarily involved in the thesis which declares man to be the
measure of all things.
Theodorus: How so?
Socrates: Why, suppose that you determine in your own mind something to be true, and declare
your opinion to me; let us assume, as he argues, that this is true to you. Now, if so, you must
either say that the rest of us are not the judges of this opinion or judgment of yours, or that
we judge you always to have a true opinion: But are there not thousands upon thousands
who, whenever you form a judgment, take up arms against you and are of an opposite
judgment and opinion, deeming that you judge falsely?
If man is the measure of all things why can there be no erroneous opinions?
Theodorus: Yes, indeed, Socrates, thousands and tens of thousands, as Homer says, who give
me a world of trouble.
Socrates: Well, but are we to assert that what you think is true to you and false to the ten
Theodorus: No other inference seems to be possible.
Socrates: And how about Protagoras himself? If neither he nor the multitude thought, as indeed
they do not think, that man is the measure of all things, must it not follow that the truth of
which Protagoras wrote would be true to no one? But if you suppose that he himself thought
this, and that the multitude does not agree with him, you must begin by allowing that in
whatever proportion the many are more than one, in that proportion his truth is more untrue
Theodorus: That would follow if the truth is supposed to vary with individual opinion.
Socrates: And the best of the joke is, that he acknowledges the truth of their opinion who believe
his own opinion to be false; for he admits that the opinions of all men are true.
Socrates: And does he not allow that his own opinion is false, if he admits that the opinion of those
who think him false is true?
Explain the preceding sentence.
Theodorus: Of course.
Socrates: Whereas the other side do not admit that they speak falsely?
Theodorus: They do not.
Socrates: And he, as may be inferred from his writings, agrees that this opinion is also true.
Socrates: Then all mankind, beginning with Protagoras, will contend, or rather, I should say that
he will allow, when he concedes that his adversary has a true opinion-Protagoras, I say, will
himself allow that neither a dog nor any ordinary man is the measure of anything which he has
not learned-am I not right?
Socrates: And the truth of Protagoras being doubted by all, will be true neither to himself to any
Theodorus: I think, Socrates, that we are running my old friend too hard.
Socrates: But do not know that we are going beyond the truth. Doubtless, as he is older, he may
be expected to be wiser than we are. And if he could only just get his head out of the world
below, he would have overthrown both of us again and again, me for talking nonsense and
you for assenting to me, and have been off and underground in a trice. But as he is not within
call, we must make the best use of our own faculties, such as they are, and speak out what
appears to us to be true. And one thing which no one will deny is, that there are great
differences in the understandings of men.
Theodorus: In that opinion I quite agree.
Socrates: And is there not most likely to be firm ground in the distinction which we were indicating
on behalf of Protagoras, viz., that most things, and all immediate sensations, such as hot, dry,
sweet, are only such as they appear; if however difference of opinion is to be allowed at all,
surely we must allow it in respect of health or disease? for every woman, child, or living
creature has not such a knowledge of what conduces to health as to enable them to cure
Theodorus: I quite agree.
Socrates: Or again, in politics, while affirming that just and unjust, honourable and disgraceful, holy
and unholy, are in reality to each state such as the state thinks and makes lawful, and that in
determining these matters no individual or state is wiser than another, still the followers of
Protagoras will not deny that in determining what is or is not expedient for the community one
state is wiser and one counsellor better that another-they will scarcely venture to maintain,
that what a city enacts in the belief that it is expedient will always be really expedient. But in
the other case, I mean when they speak of justice and injustice, piety and impiety, they are
confident that in nature these have no existence or essence of their own-the truth is that which
is agreed on at the time of the agreement, and as long as the agreement lasts; and this is the
philosophy of many who do not altogether go along with Protagoras. Here arises a new
question, Theodorus, which threatens to be more serious than the last.
Explain the absurdity that Protagoras position leads to in the arena of politics.
Theodorus: Well, Socrates, we have plenty of leisure.
Socrates: That is true, and your remark recalls to my mind an observation which I have often
made, that those who have passed their days in the pursuit of philosophy are ridiculously at
fault when they have to appear and speak in court. How natural is this!
Theodorus: What do you mean?
Socrates: I mean to say, that those who have been trained in philosophy and liberal pursuits are as
unlike those who from their youth upwards have been knocking about in the courts and such
places, as a freeman is in breeding unlike a slave.
Theodorus: In what is the difference seen?
Socrates: In the leisure spoken of by you, which a freeman can always command: he has his talk,
out in peace, and, like ourselves, he wanders at will from one subject to another, and from a
second to a third,-if the fancy takes him he begins again, as we are doing now, caring not
whether his words are many or few; his only aim is to attain the truth. But the lawyer is
always in a hurry; there is the water of the clepsydra driving him on, and not allowing him to
expatiate at will: and there is his adversary standing over him, enforcing his rights; the
indictment, which in their phraseology is termed the affidavit, is recited at the time: and from
this he must not deviate. He is a servant, and is continually disputing about a fellow servant
before his master, who is seated, and has the cause in his hands; the trial is never about some
indifferent matter, but always concerns himself; and often the race is for his life. The
consequence has been, that he has become keen and shrewd; he has learned how to flatter
his master in word and indulge him in deed; but his soul is small and unrighteous. His
condition, which has been that of a slave from his youth upwards, has deprived him of growth
and uprightness and independence; dangers and fears, which were too much for his truth and
honesty, came upon him in early years, when the tenderness of youth was unequal to them,
and he has been driven into crooked ways; from the first he has practised deception and
retaliation, and has become stunted and warped. And so he has passed out of youth into
manhood, having no soundness in him; and is now, as he thinks, a master in wisdom. Such is
the lawyer, Theodorus. Will you have the companion picture of the philosopher, who is of
our brotherhood; or shall we return to the argument? Do not let us abuse the freedom of
digression which we claim.
Theodorus: Nay, Socrates, not until we have finished what we are about; for you truly said that
we belong to a brotherhood which is free, and are not the servants of the argument; but the
argument is our servant, and must wait our leisure. Who is our judge? Or where is the
spectator having any right to censure or control us, as he might the poets?
Socrates: Then, as this is your wish, I will describe the leaders; for there is no use in talking about
the inferior sort. In the first place, the lords of philosophy have never, from their youth
upwards, known their way to the Agora, or the dicastery, or the council, or any other
political assembly; they neither see nor hear the laws or decrees, as they are called, of the
state written or recited; the eagerness of political societies in the attainment of office-clubs,
and banquets, and revels, and singing-maidens,-do not enter even into their dreams. Whether
any event has turned out well or ill in the city, what disgrace may have descended to any one
from his ancestors, male or female, are matters of which the philosopher no more knows than
he can tell, as they say, how many pints are contained in the ocean. Neither is he conscious of
his ignorance. For he does not hold aloof in order; that he may gain a reputation; but the truth
is, that the outer form of him only is in the city: his mind, disdaining the littlenesses and
nothingnesses of human things, is "flying all abroad" as Pindar says, measuring earth and
heaven and the things which are under and on the earth and above the heaven, interrogating
the whole nature of each and all in their entirety, but not condescending to anything which is
Theodorus: What do you mean, Socrates?
Socrates: I will illustrate my meaning, Theodorus, by the jest which the clever witty Thracian
handmaid is said to have made about Thales, when he fell into a well as he was looking up at
the stars. She said, that he was so eager to know what was going on in heaven, that he could
not see what was before his feet. This is a jest which is equally applicable to all philosophers.
For the philosopher is wholly unacquainted with his next-door neighbour; he is ignorant, not
only of what he is doing, but he hardly knows whether he is a man or an animal; he is
searching into the essence of man, and busy in enquiring what belongs to such a nature to do
or suffer different from any other;-I think that you understand me, Theodorus?
Theodorus: I do, and what you say is true.
Socrates: And thus, my friend, on every occasion, private as well as public, as I said at first, when
he appears in a law-court, or in any place in which he has to speak of things which are at his
feet and before his eyes, he is the jest, not only of Thracian handmaids but of the general
herd, tumbling into wells and every sort of disaster through his inexperience. His
awkwardness is fearful, and gives the impression of imbecility. When he is reviled, he has
nothing personal to say in answer to the civilities of his adversaries, for he knows no scandals
of any one, and they do not interest him; and therefore he is laughed at for his sheepishness;
and when others are being praised and glorified, in the simplicity of his heart he cannot help
going into fits of laughter, so that he seems to be a downright idiot. When he hears a tyrant or
king eulogized, he fancies that he is listening to the praises of some keeper of cattle-a
swineherd, or shepherd, or perhaps a cowherd, who is congratulated on the quantity of milk
which he squeezes from them; and he remarks that the creature whom they tend, and out of
whom they squeeze the wealth, is of a less traitable and more insidious nature. Then, again,
he observes that the great man is of necessity as ill-mannered and uneducated as any
shepherd-for he has no leisure, and he is surrounded by a wall, which is his mountain-pen.
Hearing of enormous landed proprietors of ten thousand acres and more, our philosopher
deems this to be a trifle, because he has been accustomed to think of the whole earth; and
when they sing the, praises of family, and say that someone is a gentleman because he can
show seven generations of wealthy ancestors, he thinks that their sentiments only betray a dull
and narrow vision in those who utter them, and who are not educated enough to look at the
whole, nor to consider that every man has had thousands and ten thousands of progenitors,
and among them have been rich and poor, kings and slaves, Hellenes and barbarians,
innumerable. And when people pride themselves on having a pedigree of twenty-five
ancestors, which goes back to Heracles, the son of Amphitryon, he cannot understand their
poverty of ideas. Why are they unable to calculate that Amphitryon had a twenty-fifth
ancestor, who might have been anybody, and was such as fortune made him and he had a
fiftieth, and so on? He amuses himself with the notion that they cannot count, and thinks that a
little arithmetic would have got rid of their senseless vanity. Now, in all these cases our
philosopher is derided by the vulgar, partly because he is thought to despise them, and also
because he is ignorant of what is before him, and always at a loss.
Theodorus: That is very true, Socrates.
Socrates: But, O my friend, when he draws the other into upper air, and gets him out of his pleas
and rejoinders into the contemplation of justice and injustice in their own nature and in their
difference from one another and from all other things; or from the commonplaces about the
happiness of a king or of a rich man to the consideration of government, and of human
happiness and misery in general-what they are, and how a man is to attain the one and avoid
the other-when that narrow, keen, little legal mind is called to account about all this, he gives
the philosopher his revenge; for dizzied by the height at which he is hanging, whence he looks
down into space, which is a strange experience to him, he being dismayed, and lost, and
stammering broken words, is laughed at, not by Thracian handmaidens or any other
uneducated persons, for they have no eye for the situation, but by every man who has not
been brought up a slave. Such are the two characters, Theodorus: the one of the freeman,
who has becomes trained in liberty and leisure, whom you call the philosopher-him we cannot
blame because he appears simple and of no account when he has to perform some menial
task, such as packing up bed-clothes, or flavouring a sauce or fawning speech; the other
character is that of the man who is able to do all this kind of service smartly and neatly, but
knows not how to wear his cloak like a gentleman; still less with the music of discourse can
he hymn the true life aright which is lived by immortals or men blessed of heaven.
Theodorus: If you could only persuade everybody, Socrates, as you do me, of the truth of your
words, there would be more peace and fewer evils among men.
Socrates: Evils, Theodorus, can never pass away; for there must always remain something which
is antagonistic to good. Having no place among the gods in heaven, of necessity they hover
around the mortal nature, and this earthly sphere. Wherefore we ought to fly away from earth
to heaven as quickly as we can; and to fly away is to become like God, as far as this is
possible; and to become like him, is to become holy, just, and wise. But, O my friend, you
cannot easily convince mankind that they should pursue virtue or avoid vice, not merely in
order that a man may seem to be good, which is the reason given by the world, and in my
judgment is only a repetition of an old wives fable. Whereas, the truth is that God is never in
any way unrighteous-he is perfect righteousness; and he of us who is the most righteous is
most like him. Herein is seen the true cleverness of a man, and also his nothingness and want
of manhood. For to know this is true wisdom and virtue, and ignorance of this is manifest
folly and vice. All other kinds of wisdom or cleverness, which seem only, such as the wisdom
of politicians, or the wisdom of the arts, are coarse and vulgar. The unrighteous man, or the
sayer and doer of unholy things, had far better not be encouraged in the illusion that his
roguery is clever; for men glory in their shame -they fancy that they hear others saying of
them, "These are not mere good-for nothing persons, mere burdens of the earth, but such as
men should be who mean to dwell safely in a state." Let us tell them that they are all the more
truly what they do not think they are because they do not know it; for they do not know the
penalty of injustice, which above all things they ought to know-not stripes and death, as they
suppose, which evil-doers often escape, but a penalty which cannot be escaped.
Theodorus: What is that?
Socrates: There are two patterns eternally set before them; the one blessed and divine, the other
godless and wretched: but they do not see them, or perceive that in their utter folly and
infatuation they are growing like the one and unlike the other, by reason of their evil deeds;
and the penalty is, that they lead a life answering to the pattern which they are growing like.
And if we tell them, that unless they depart from their cunning, the place of innocence will not
receive them after death; and that here on earth, they will live ever in the likeness of their own
evil selves, and with evil friends-when they hear this they in their superior cunning will seem to
be listening to the talk of idiots.
Theodorus: Very true, Socrates.
Socrates: Too true, my friend, as I well know; there is, however, one peculiarity in their case:
when they begin to reason in private about their dislike of philosophy, if they have the
courage to hear the argument out and do not run away, they grow at last strangely
discontented with themselves; their rhetoric fades away, and they become helpless as
children. These however are digressions from which we must now desist, or they will
overflow, and drown the original argument; to which, if you please, we will now return.
Theodorus: For my part, Socrates, I would rather have the digressions, for at my age I find them
easier to follow; but if you wish, let us go back to the argument.
Socrates: Had we not reached the point at which the partisans of the perpetual flux, who say that
things are as they seem to each one, were confidently maintaining that the ordinances which
the state commanded 2nd thought just, were just to the state which imposed them, while they
were in force; this was especially asserted of justice; but as to the good, no one had any
longer the hardihood to contend of any ordinances which the state thought and enacted to be
good that these, while they were in force, were really good;-he who said so would be playing
with the name "good," and would, not touch the real question-it would be a mockery, would
Theodorus: Certainly it would.
Socrates: He ought not to speak of the name, but of the thing which is contemplated under the
Socrates: Whatever be the term used, the good or expedient is the aim of legislation, and as far as
she has an opinion, the state imposes all laws with a view to the greaquiz expediency; can
legislation have any other aim?
Theodorus: Certainly not.
Socrates: But is the aim attained always? do not mistakes often happen?
Theodorus: Yes, I think that there are mistakes.
Socrates: The possibility of error will be more distinctly recognized, if we put the question in
reference to the whole class under which the good or expedient fall That whole class has to
do with the future, and laws are passed under the idea that they will be useful in after-time;
which, in other words, is the future.
Theodorus: Very true.
Socrates: Suppose now, that we ask Protagoras, or one of his disciples, a question:-O,
Protagoras, we will say to him, Man is, as you declare, the measure of all things-white,
heavy, light: of all such things he is the judge; for he has the criterion of them in himself, and
when he thinks that things are such as he experiences them to be, he thinks what is and is true
to himself. Is it not so?
Socrates: And do you extend your doctrine, Protagoras (as we shall further say), to the future as
well as to the present; and has he the criterion not only of what in his opinion is but of what
will be, and do things always happen to him as he expected? For example, take the case of
heat:-When an ordinary man thinks that he is going to have a fever, and that this kind of heat
is coming on, and another person, who is a physician, thinks the contrary, whose opinion is
likely to prove right? Or are they both right?-he will have a heat and fever in his own
judgment, and not have a fever in the physician's judgment?
Theodorus: How ludicrous!
Socrates: And the vinegrower, if I am not mistaken, is a better judge of the sweetness or dryness
of the vintage which is not yet gathered than the harp-player?
Socrates: And in musical composition-the musician will know better than the training master what
the training master himself will hereafter think harmonious or the reverse?
Theodorus: Of course.
Socrates: And the cook will be a better judge than the guest, who is not a cook, of the pleasure to
be derived from the dinner which is in preparation; for of present or past pleasure we are not
as yet arguing; but can we say that every one will be to himself the best judge of the pleasure
which will seem to be and will be to him in the future?-nay, would not you, Protagoras, better
guess which arguments in a court would convince any one of us than the ordinary man?
Theodorus: Certainly, Socrates, he used to profess in the strongest manner that he was the
superior of all men in this respect.
Socrates: To be sure, friend: who would have paid a large sum for the privilege of talking to him, if
he had really persuaded his visitors that neither a prophet nor any other man was better able
to judge what will be and seem to be in the future than every one could for himself?
Theodorus: Who indeed?
Socrates: And legislation and expediency are all concerned with the future; and every one will
admit that states, in passing laws, must often fail of their highest interests?
Theodorus: Quite true.
Socrates: Then we may fairly argue against your master, that he must admit one man to be wiser
than another, and that the wiser is a measure: but I, who know nothing, am not at all obliged
to accept the honour which the advocate of Protagoras was just now forcing upon me,
whether I would or not, of being a measure of anything.
Theodorus: That is the best refutation of him, Socrates; although he is also caught when he
ascribes truth to the opinions of others, who give the lie direct to his own opinion.
Socrates: There are many ways, Theodorus, in which the doctrine that every opinion of: every
man is true may be refuted; but there is more difficulty, in proving that states of feeling, which
are present to a man, and out of which arise sensations and opinions in accordance with
them, are also untrue. And very likely I have been talking nonsense about them; for they may
be unassailable, and those who say that there is clear evidence of them, and that they are
matters of knowledge, may probably be right; in which case our friend Theaetetus was not so
far from the mark when he identified perception and knowledge. And therefore let us draw
nearer, as the advocate of Protagoras desires; and the truth of the universal flux a ring: is the
theory sound or not? at any rate, no small war is raging about it, and there are combination
not a few.
Theodorus: No small, war, indeed, for in most the sect makes rapid strides, the disciples of
Heracleitus are most energetic. upholders of the doctrine.
Socrates: Then we are the more bound, my dear Theodorus, to examine the question from the
foundation as it is set forth by themselves.
Theodorus: Certainly we are. About these speculations of Heracleitus, which, as you say, are as
old as Homer, or even older still, the Ephesians themselves, who profess to know them, are
downright mad, and you cannot talk with them on the subject. For, in accordance with their
text-books, they are always in motion; but as for dwelling upon an argument or a question,
and quietly asking and answering in turn, they can no more do so than they can fly; or rather,
the determination of these fellows not to have a particle of rest in them is more than the
utmost powers of negation can express. If you ask any of them a question, he will produce,
as from a quiver, sayings brief and dark, and shoot them at you; and if you inquire the reason
of what he has said, you will be hit by some other newfangled word, and will make no way
with any of them, nor they with one another; their great care is, not to allow of any settled
principle either in their arguments or in their minds, conceiving, as I imagine, that any such
principle would be stationary; for they are at war with the stationary, and do what they can to
drive it out everywhere.
Socrates: I suppose, Theodorus, that you have only seen them when they were fighting, and have
never stayed with them in time of peace, for they are no friends of yours; and their peace
doctrines are only communicated by them at leisure, as I imagine, to those disciples of theirs
whom they want to make like themselves.
Theodorus: Disciples! my good sir, they have none; men of their sort are not one another's
disciples, but they grow up at their own sweet will, and get their inspiration anywhere, each of
them saying of his neighbour that he knows nothing. Fro these men, then, as I was going to
remark, you will never get a reason, whether with their will or without their will; we must take
the question out of their hands, and make the analysis ourselves, as if we were doing
Socrates: Quite right too; but as touching the aforesaid problem, have we not heard from the
ancients, who concealed their wisdom from the many in poetical figures, that Oceanus and
Tethys, the origin of all things, are streams, and that nothing is at rest? And now the moderns,
in their superior wisdom, have declared the same openly, that the cobbler too may hear and
learn of them, and no longer foolishly imagine that some things are at rest and others in
motion-having learned that all is motion, he will duly honour his teachers. I had almost
forgotten the opposite doctrine, Theodorus,
Alone Being remains unmoved, which is the name for the all. This is the language of
Parmenides, Melissus, and their followers, who stoutly maintain that all being is one and
self-contained, and has no place which to move. What shall we do, friend, with all these
people; for, advancing step by step, we have imperceptibly got between the combatants,
and, unless we can protect our retreat, we shall pay the penalty of our rashness-like the
players in the palaestra who are caught upon the line, and are dragged different ways by the
two parties. Therefore I think that we had better begin by considering those whom we first
accosted, "the river-gods," and, if we find any truth in them, we will help them to pull us over,
and try to get away from the others. But if the partisans of "the whole" appear to speak more
truly, we will fly off from the party which would move the immovable, to them. And if I find
that neither of them have anything reasonable to say, we shall be in a ridiculous position,
having so great a conceit of our own poor opinion and rejecting that of ancient and famous
men. O Theodorus, do you think that there is any use in proceeding when the danger is so
Explain the positions of these two combatants in their philosophic war.
Theodorus: Nay, Socrates, not to examine thoroughly what the two parties have to say would be
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? 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?
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."
Explain the two types of motion.
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
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 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 Way, 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.
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?
Why does perception become impossible if all is in flux?
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.
What conclusion does Socrates come to regarding the nature of knowledge?
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
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
Theaetetus: Very well; do so if you will.
Socrates: Then now, Theaetetus, take another view of the subject: you answered that knowledge
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?
Socrates: And that either of them is different from the other, and the same with itself?
Socrates: And that both are two and each of them one?
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
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?
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?
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?
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.
Socrates: And can a man attain truth who fails of attaining being?
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?
What reasoning does Socrates use to come to the conclusion that knowledge does not consist in impressions of sense.
End of First Reading.
Socrates: And would you call the two processes by the same name, when there is so great
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?
Socrates: Which, as we say, has no part in the attainment of truth any more of being?
Theaetetus: Certainly not.
Socrates: And therefore not in. science or knowledge?
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
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 over again in a new way.
Theaetetus: Begin again, Socrates,-at least if you think that there is the slighquiz 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.
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
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
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
Theaes. 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
Socrates: But is there any parallel to this?
Theaetetus: What do you mean?
Socrates: Can a man see something and yet see nothing?
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 nonexisting things?
Theaetetus: I do not.
Socrates: He then who sees some one thing, sees something which is?
Socrates: And he who hears anything, hears some one thing, and hears that which is?
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?
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?
Socrates: And he who thinks of nothing, does not think at all?
Socrates: Then no one can think that which is not, either as a self-existent substance or as a
predicate of something else?
Explain why it is difficult to conceive of our minds as thinking a false thought.
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?
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
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
Theaetetus: I am.
Socrates: It is possible then upon your view for the mind to conceive of one thing as another?
Socrates: But must not the mind, or thinking power, which misplaces them, have a conception
either of both objects or of one of them?
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
Theaetetus: I agree.
Socrates: Then when any one thinks of one thing as another, he is saying to himself that one thing
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?
Socrates: 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?
Theaetetus: Certainly not.
Socrates: 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.
Theaetetus: I will give up the word "other," Socrates; and I agree to what you say.
Socrates: If a man has both of them in his thoughts, he cannot think that the one of them is the
Socrates: Neither, if he has one of them only in his mind and not the other, can he think that one is
Theaetetus: True; for we should have to suppose that he apprehends that which is not in his
thoughts at all.
Socrates: 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
Socrates: But if, Theaetetus, this is not admitted, we shall be driven into many absurdities.
Theaetetus: What are they?
Socrates: I will not tell you until I have endeavoured to consider the matter from every point of
view. For I should be ashamed of us if we were driven in our perplexity to admit the absurd
consequences of which I speak. But if we find the solution, and get away from them, we may
regard them only as the difficulties of others, and the ridicule will not attach to us. On the
other hand, if we utterly fail, I suppose that we must be humble, and allow the argument to
trample us under foot, as the sea-sick passenger is trampled upon by the sailor, and to do
anything to us. Listen, then, while I tell you how I hope to find a way out of our difficulty.
Theaetetus: Let me hear.
Socrates: I think that we were wrong in denying that a man could think what he knew to be what
he did not know; and that there is a way in which such a deception is possible.
Theaetetus: You mean to say, as I suspected at the time, that I may know Socrates, and at a
distance see some one who is unknown to me, and whom I mistake for him-them the
deception will occur?
Socrates: But has not that position been relinquished by us, because involving the absurdity that
we should know and not know the things which we know?
Socrates: Let us make the assertion in another form, which may or may not have a favourable
issue; but as we are in a great strait, every argument should be turned over and quized. Tell
me, then, whether I am right in saying that you may learn a thing which at one time you did
Theaetetus: Certainly you may.
Socrates: And another and another?
Socrates: I would have you imagine, then, that there exists in the mind of man a block of wax,
which is of different sizes in different men; harder, moister, and having more or less of purity
in one than another, and in some of an intermediate quality.
Theaetetus: I see.
Socrates: Let us say that this tablet is a gift of Memory, the mother of the Muses; and that when
we wish to remember anything which we have seen, or heard, or thought in our own minds,
we hold the wax to the perceptions and thoughts, and in that material receive the impression
of them as from the seal of a ring; and that we remember and know what is imprinted as long
as the image lasts; but when the image is effaced, or cannot be taken, then we forget and do
Theaetetus: Very good.
Socrates: Now, when a person has this knowledge, and is considering something which he sees or
hears, may not false opinion arise in the following manner?
Theaetetus: In what manner?
Socrates: When he thinks what he knows, sometimes to be what he knows, and sometimes to be
what he does not know. We were wrong before in denying the possibility of this.
Theaetetus: And how would you amend the former statement?
Socrates: I should begin by making a list of the impossible cases which must be excluded. (1) No
one can think one thing to be another when he does not perceive either of them, but has the
memorial or seal of both of them in his mind; nor can any mistaking of one thing for another
occur, when he only knows one, and does not know, and has no impression of the other; nor
can he think that one thing which he does not know is another thing which he does not know,
or that what he does not know is what he knows; nor (2) that one thing which he perceives is
another thing which he perceives, or that something which he perceives is something which he
does not perceive; or that something which he does not perceive is something else which he
does not perceive; or that something which he does not perceive is something which he
perceives; nor again (3) can he think that something which he knows and perceives, and of
which he has the impression coinciding with sense, is something else which he knows and
perceives, and of which he has the impression coinciding with sense;-this last case, if
possible, is still more inconceivable than the others; nor (4) can he think that something which
he knows and perceives, and of which he has the memorial coinciding with sense, is
something else which he knows; nor so long as these agree, can he think that a thing which he
knows and perceives is another thing which he perceives; or that a thing which he does not
know and does not perceive, is the same as another thing which he does not know and does
not perceive;-nor again, can he suppose that a thing which he does not know and does not
perceive is the same as another thing which he does not know; or that a thing which he does
not know and does not perceive is another thing which he does not perceive:-All these utterly
and absolutely exclude the possibility of false opinion. The only cases, if any, which remain,
are the following.
Summarize the "four impossible cases."
Theaetetus: What are they? If you tell me, I may perhaps understand you better; but at present I
am unable to follow you.
Socrates: A person may think that some things which he knows, or which he perceives and does
not know, are some other things which he knows and perceives; or that some things which he
knows and perceives, are other things which he knows and perceives.
Why are these two instances the only two possible sources of error?
Theaetetus: I understand you less than ever now. Ya got that right!
Socrates: Hear me once more, then:-I, knowing Theodorus, and remembering in my own mind
what sort of person he is, and also what sort of person Theaetetus is, at one time see them,
and at another time do not see them, and sometimes I touch them, and at another time not, or
at one time I may hear them or perceive them in some other way, and at another time not
perceive them, but still I remember them, and know them in my own mind.
Theaetetus: Very true.
Socrates: Then, first of all, I want you to understand that a man may or may not perceive sensibly
that which he knows.
Socrates: And that which he does not know will sometimes not be perceived by him and
sometimes will be perceived and only perceived?
Theaetetus: That is also true.
Socrates: See whether you can follow me better now: Socrates can recognize Theodorus and
Theaetetus, but he sees neither of them, nor does he perceive them in any other way; he
cannot then by any possibility imagine in his own mind that Theaetetus is Theodorus. Am I
Theaetetus: You are quite right.
Socrates: Then that was the first case of which I spoke.
Socrates: The second case was, that I, knowing one of you and not knowing the other, and
perceiving neither, can never think him whom I know to be him whom I do not know.
Socrates: In the third case, not knowing and not perceiving either of you, I cannot think that one
of you whom I do not know is the other whom I do not know. I need not again go over the
catalogue of excluded cases, in which I cannot form a false opinion about you and
Theodorus, either when I know both or when I am in ignorance of both, or when I know one
and not the other. And the same of perceiving: do you understand me?
Theaetetus: I do.
Socrates: The only possibility of erroneous opinion is, when knowing you and Theodorus, and
having on the waxen block the impression of both of you given as by a seal, but seeing you
imperfectly and at a distance, I try to assign the right impression of memory to the right visual
impression, and to fit this into its own print: if I succeed, recognition will take place; but if I
fad and transpose them, putting the foot into the wrong shoe-that is to say, putting the vision
of either of you on to the wrong impression, or if my mind, like the sight in a mirror, which is
transferred from right to left, err by reason of some similar affection, then "heterodoxy" and
false opinion ensues.
How do false impressions arise?
Theaetetus: Yes, Socrates, you have described the nature of opinion with wonderful exactness.
Socrates: Or again, when I know both of you, and perceive as well as know one of you, but not
the other, and my knowledge of him does not accord with perception-that was the case put
by me just now which you did not understand
Theaetetus: No, I did not.
Socrates: I meant to say, that when a person knows and perceives one of you, his knowledge
coincides with his perception, he will never think him to be some other person, whom he
knows and perceives, and the knowledge of whom coincides with his perception-for that also
was a case supposed.
Socrates: But there was an omission of the further case, in which, as we now say, false opinion
may arise, when knowing both, and seeing, or having some other sensible perception of both,
I fail in holding the seal over against the corresponding sensation; like a bad archer, I miss
and fall wide of the mark-and this is called falsehood.
Theaetetus: Yes; it is rightly so called.
Socrates: When, therefore, perception is present to one of the seals or impressions but not to the
other, and the mind fits the seal of the absent perception on the one which is present, in any
case of this sort the mind is deceived; in a word, if our view is sound, there can be no error
or deception about things which a man does not know and has never perceived, but only in
things which are known and perceived; in these alone opinion turns and twists about, and
becomes alternately true and false;-true when the seals and impressions of sense meet straight
and opposite-false when they go awry and crooked.
Theaetetus: And is not that, Socrates, nobly said?
Socrates: Nobly! yes; but wait a little and hear the explanation, and then you will say so with more
reason; for to think truly is noble and to be deceived is base.
Socrates: And the origin of truth and error is as follows:-When the wax in the soul of any one is
deep and abundant, and smooth and perfectly tempered, then the impressions which pass
through the senses and sink into the heart of the soul, as Homer says in a parable, meaning to
indicate the likeness of the soul to wax (Kerh Kerhos); these, I say, being pure and clear, and
having a sufficient depth of wax, are also lasting, and minds, such as these, easily learn and
easily retain, and are not liable to confusion, but have true thoughts, for they have plenty of
room, and having clear impressions of things, as we term them, quickly distribute them into
their proper places on the block. And such men are called wise. Do you agree?
Socrates: But when the heart of any one is shaggy-a quality which the all-wise poet commends, or
muddy and of impure wax, or very soft, or very hard, then there is a corresponding defect in
the mind -the soft are good at learning, but apt to forget; and the hard are the reverse; the
shaggy and rugged and gritty, or those who have an admixture of earth or dung in their
composition, have the impressions indistinct, as also the hard, for there is no depth in them;
and the soft too are indistinct, for their impressions are easily confused and effaced. Yet
greater is the indistinctness when they are all jostled together in a little soul, which has no
room. These are the natures which have false opinion; for when they see or hear or think of
anything, they are slow in assigning the right objects to the right impressions-in their stupidity
they confuse them, and are apt to see and hear and think amiss-and such men are said to be
deceived in their knowledge of objects, and ignorant.
What types of wax are minds made of and what mental characteristics are thought to result from the various types?
Theaetetus: No man, Socrates, can say anything truer than that.
Socrates: Then now we may admit the existence of false opinion in us?
Socrates: And of true opinion also?
Socrates: We have at length satisfactorily proven beyond a doubt there are these two sorts of
Socrates: Alas, Theaetetus, what a tiresome creature is a man who is fond of talking!
Theaetetus: What makes you say so?
Socrates: Because I am disheartened at my own stupidity and tiresome garrulity; for what other
term will describe the habit of a man who is always arguing on all sides of a question; whose
dulness cannot be convinced, and who will never leave off?
Theaetetus: But what puts you out of heart?
Socrates: I am not only out of heart, but in positive despair; for I do not know what to answer if
any one were to ask me:-O Socrates, have you indeed discovered that false opinion arises
neither in the comparison of perceptions with one another nor yet in thought, but in union of
thought and perception? Yes, I shall say, with the complacence of one who thinks that he has
made a noble discovery.
Theaetetus: I see no reason why we should be ashamed of our demonstration, Socrates.
Socrates: He will say: You mean to argue that the man whom we only think of and do not see,
cannot be confused with the horse which we do not see or touch, but only think of and do
not perceive? That I believe to be my meaning, I shall reply.
Theaetetus: Quite right.
Socrates: Well, then, he will say, according to that argument, the number eleven, which is only
thought, never be mistaken for twelve, which is only thought: How would you answer him?
Theaetetus: I should say that a mistake may very likely arise between the eleven or twelve which
are seen or handled, but that no similar mistake can arise between the eleven and twelve
which are in the mind.
Why is it possible to confuse 11 and 12 in the hand, but not in the mind?
Socrates: Well, but do you think that no one ever put before his own mind five and seven, -I do
not mean five or seven men or horses, but five or seven in the abstract, which, as we say, are
recorded on the waxen block, and in which false opinion is held to be impossible; did no man
ever ask himself how many these numbers make when added together, and answer that they
are eleven, while another thinks that they are twelve, or would all agree in thinking and saying
that they are twelve?
Theaetetus: Certainly not; many would think that they are eleven, and in the higher numbers the
chance of error is greater still; for I assume you to be speaking of numbers in general.
Socrates: Exactly; and I want you to consider whether this does not imply that the twelve in the
waxen block are supposed to be eleven?
Theaetetus: Yes, that seems to be the case.
Socrates: Then do we not come back to the old difficulty? For he who makes such a mistake
does think one thing which he knows to be another thing which he knows; but this, as we
said, was impossible, and afforded an irresistible proof of the non-existence of false opinion,
because otherwise the same person would inevitably know and not know the same thing at
the same time.
Theaetetus: Most true.
Socrates: Then false opinion cannot be explained as a confusion of thought and sense, for in that
case we could not have been mistaken about pure conceptions of thought; and thus we are
obliged to say, either that false opinion does not exist, or that a man may not know that which
he knows;-which alternative do you prefer?
Theaetetus: It is hard to determine, Socrates.
Socrates: And yet the argument will scarcely admit of both. But, as we are at our wits' end,
suppose that we do a shameless thing?
Theaetetus: What is it?
Socrates: Let us attempt to explain the verb "to know."
Theaetetus: And why should that be shameless?
Socrates: You seem not to be aware that the whole of our discussion from the very beginning has
been a search after knowledge, of which we are assumed not to know the nature.
Theaetetus: Nay, but I am well aware.
Socrates: And is it not shameless when we do not know what knowledge is, to be explaining the
verb "to know"? The truth is, Theaetetus, that we have long been infected with logical
impurity. Thousands of times have we repeated the words "we know," and "do not know,"
and "we have or have not science or knowledge," as if we could understand what we are
saying to one another, so long as we remain ignorant about knowledge; and at this moment
we are using the words "we understand," "we are ignorant," as though we could still employ
them when deprived of knowledge or science.
Why is Socrates ashamed that he does not know what "to know" means?
Theaetetus: But if you avoid these expressions, Socrates, how will you ever argue at all?
Socrates: I could not, being the man I am. The case would be different if I were a true hero of
dialectic: and O that such an one were present! for he would have told us to avoid the use of
these terms; at the same time he would not have spared in you and me the faults which I have
noted. But, seeing that we are no great wits, shall I venture to say what knowing is? for I
think that the attempt may be worth making.
Theaetetus: Then by all means venture, and no one shall find fault with you for using the
Socrates: You have heard the common explanation of the verb "to know"?
Theaetetus: I think so, but I do not remember it at the moment.
Socrates: They explain the word "to know" as meaning "to have knowledge."
Socrates: I should like to make a slight change, and say "to possess" knowledge.
Theaetetus: How do the two expressions differ?
Socrates: Perhaps there may be no difference; but still I should like you to hear my view, that you
may help me to quiz it.
Theaetetus: I will, if I can.
Socrates: I should distinguish "having" from "possessing": for example, a man may buy and keep
under his control a garment which he does not wear; and then we should say, not that he has,
but that he possesses the garment.
Theaetetus: It would be the correct expression.
Socrates: Well, may not a man "possess" and yet not "have" knowledge in the sense of which I am
speaking? As you may suppose a man to have caught wild birds -doves or any other
birds-and to be keeping them in an aviary which he has constructed at home; we might say of
him in one sense, that he always has them because he possesses them, might we not?
What does Socrates try to illustrate using the aviary example?
Socrates: And yet, in another sense, he has none of them; but they are in his power, and he has
got them under his hand in an enclosure of his own, and can take and have them whenever he
likes;-he can catch any which he likes, and let the bird go again, and he may do so as often as
Socrates: Once more, then, as in what preceded we made a sort of waxen figment in the mind, so
let us now suppose that in the mind of each man there is an aviary of all sorts of birds-some
flocking together apart from the rest, others in small groups, others solitary, flying anywhere
Theaetetus: Let us imagine such an aviary-and what is to follow?
Socrates: We may suppose that the birds are kinds of knowledge, and that when we were
children, this receptacle was empty; whenever a man has gotten and detained in the enclosure
a kind of knowledge, he may be said to have learned or discovered the thing which is the
subject of the knowledge: and this is to know.
Socrates: And further, when any one wishes to catch any of these knowledges or sciences, and
having taken, to hold it, and again to let them go, how will he express himself?-will he
describe the "catching" of them and the original "possession" in the same words? I will make
my meaning clearer by an example:-You admit that there is an art of arithmetic?
Theaetetus: To be sure.
Socrates: Conceive this under the form of a hunt after the science of odd and even in general.
Theaetetus: I follow.
Socrates: Having the use of the art, the arithmetician, if I am not mistaken, has the conceptions of
number under his hand, and can transmit them to another.
Socrates: And when transmitting them he may be said to teach them, and when receiving to learn
them, and when receiving to learn them, and when having them in possession in the aforesaid
aviary he may be said to know them.
Socrates: Attend to what follows: must not the perfect arithmetician know all numbers, for he has
the science of all numbers in his mind?
Socrates: And he can reckon abstract numbers in his head, or things about him which are
Theaetetus: Of course he can.
Socrates: And to reckon is simply to consider how much such and such a number amounts to?
Theaetetus: Very true.
Socrates: And so he appears to be searching into something which he knows, as if he did not
know it, for we have already admitted that he knows all numbers;-you have heard these
perplexing questions raised?
Theaetetus: I have.
Socrates: May we not pursue the image of the doves, and say that the chase after knowledge is of
two kinds? one kind is prior to possession and for the sake of possession, and the other for
the sake of taking and holding in the hands that which is possessed already. And thus, when a
man has learned and known something long ago, he may resume and get hold of the
knowledge which he has long possessed, but has not at hand in his mind.
Socrates: That was my reason for asking how we ought to speak when an arithmetician sets about
numbering, or a grammarian about reading? Shall we say, that although he knows, he comes
back to himself to learn what he already knows?
Theaetetus: It would be too absurd, Socrates.
Socrates: Shall we say then that he is going to read or number what he does not know, although
we have admitted that he knows all letters and all numbers?
Theaetetus: That, again, would be an absurdity.
Socrates: Then shall we say that about names we care nothing?-any one may twist and turn the
words "knowing" and "learning" in any way which he likes, but since we have determined that
the possession of knowledge is not the having or using it, we do assert that a man cannot not
possess that which he possesses; and, therefore, in no case can a man not know that which
he knows, but he may get a false opinion about it; for he may have the knowledge, not of this
particular thing, but of some other;-when the various numbers and forms of knowledge are
flying about in the aviary, and wishing to capture a certain sort of knowledge out of the
general store, he takes the wrong one by mistake, that is to say, when he thought eleven to be
twelve, he got hold of the ringdove which he had in his mind, when he wanted the pigeon.
Theaetetus: A very rational explanation.
Socrates: But when he catches the one which he wants, then he is not deceived, and has an
opinion of what is, and thus false and true opinion may exist, and the difficulties which were
previously raised disappear. I dare say that you agree with me, do you not?
Socrates: And so we are rid of the difficulty of a man's not knowing what he knows, for we are
not driven to the inference that he does not possess what he possesses, whether he be or be
not deceived. And yet I fear that a greater difficulty is looking in at the window.
Theaetetus: What is it?
Socrates: How can the exchange of one knowledge for another ever become false opinion?
Theaetetus: What do you mean?
Socrates: In the first place, how can a man who has the knowledge of anything be ignorant of that
which he knows, not by reason of ignorance, but by reason of his own knowledge? And,
again, is it not an extreme absurdity that he should suppose another thing to be this, and this
to be another thing;-that, having knowledge present with him in his mind, he should still know
nothing and be ignorant of all things?-you might as well argue that ignorance may make a man
know, and blindness make him see, as that knowledge can make him ignorant.
Theaetetus: Perhaps, Socrates, we may have been wrong in making only forms of knowledge
our birds: whereas there ought to have been forms of ignorance as well, flying about together
in the mind, and then he who sought to take one of them might sometimes catch a form of
knowledge, and sometimes a form of ignorance; and thus he would have a false opinion from
ignorance, but a true one from knowledge, about the same thing.
Socrates: I cannot help praising you, Theaetetus, and yet I must beg you to reconsider your
words. Let us grant what you say-then, according to you, he who takes ignorance will have a
false opinion-am I right?
Socrates: He will certainly not think that he has a false opinion?
Theaetetus: Of course not.
Socrates: He will think that his opinion is true, and he will fancy that he knows the things about
which he has been deceived?
Socrates: Then he will think that he has captured knowledge and not ignorance?
Socrates: And thus, after going a long way round, we are once more face to face with our original
difficulty. The hero of dialectic will retort upon us:-"O my excellent friends, he will say,
laughing, if a man knows the form of ignorance and the form of knowledge, can he think that
one of them which he knows is the other which he knows? or, if he knows neither of them,
can he think that the one which he knows not is another which he knows not? or, if he knows
one and not the other, can he think the one which he knows to be the one which he does not
know? or the one which he does not know to be the one which he knows? or will you tell me
that there are other forms of knowledge which distinguish the right and wrong birds, and
which the owner keeps in some other aviaries or graven on waxen blocks according to your
foolish images, and which he may be said to know while he possesses them, even though he
have them not at hand in his mind? And thus, in a perpetual circle, you will be compelled to
go round and round, and you will make no progress." What are we to say in reply,
Theaetetus: Indeed, Socrates, I do not know what we are to say.
Socrates: Are not his reproaches just, and does not the argument truly show that we are wrong in
seeking for false opinion until we know what knowledge is; that must be first ascertained;
then, the nature of false opinion?
Theaetetus: I cannot but agree with you, Socrates, so far as we have yet gone.
Socrates: Then, once more, what shall we say that knowledge is?-for we are not going to lose
heart as yet.
Theaetetus: Certainly, I shall not lose heart, if you do not.
Socrates: What definition will be most consistent with our former views?
Theaetetus: I cannot think of any but our old one, Socrates.
Socrates: What was it?
Theaetetus: Knowledge was said by us to be true opinion; and true opinion is surely unerring,
and the results which follow from it are all noble and good.
Socrates: He who led the way into the river, Theaetetus, said "The experiment will show"; and
perhaps if we go forward in the search, we may stumble upon the thing which we are looking
for; but if we stay where we are, nothing will come to light.
Theaetetus: Very true; let us go forward and try.
Socrates: The trail soon comes to an end, for a whole profession is against us.
Theaetetus: How is that, and what profession do you mean?
Socrates: The profession of the great wise ones who are called orators and lawyers; for these
persuade men by their art and make them think whatever they like, but they do not teach
them. Do you imagine that there are any teachers in the world so clever as to be able to
convince others of the truth about acts of robbery or violence, of which they were not
eyewitnesses, while a little water is flowing in the clepsydra?
Theaetetus: Certainly not, they can only persuade them.
Socrates: And would you not say that persuading them is making them have an opinion?
Theaetetus: To be sure.
Socrates: When, therefore, judges are justly persuaded about matters which you can know only
by seeing them, and not in any other way, and when thus judging of them from report they
attain a true opinion about them, they judge without knowledge and yet are rightly persuaded,
if they have judged well.
Socrates: And yet, O my friend, if true opinion in law courts and knowledge are the same, the
perfect judge could not have judged rightly without knowledge; and therefore I must infer that
they are not the same.
Theaetetus: That is a distinction, Socrates, which I have heard made by some one else, but I had
forgotten it. He said that true opinion, combined with reason, was knowledge, but that the
opinion which had no reason was out of the sphere of knowledge; and that things of which
there is no rational account are not knowable-such was the singular expression which he
used-and that things which have a reason or explanation are knowable.
Socrates: Excellent; but then, how did he distinguish between things which are and are not
"knowable"? I wish that you would repeat to me what he said, and then I shall know whether
you and I have heard the same tale.
Theaetetus: I do not know whether I can recall it; but if another person would tell me, I think
that I could follow him.
Socrates: Let me give you, then, a dream in return for a dream:-Methought that I too had a
dream, and I heard in my dream that the primeval letters or elements out of which you and I
and all other things are compounded, have no reason or explanation; you can only name
them, but no predicate can be either affirmed or denied of them, for in the one case existence,
in the other non-existence is already implied, neither of which must be added, if you mean to
speak of this or that thing by itself alone. It should not be called itself, or that, or each, or
alone, or this, or the like; for these go about everywhere and are applied to all things, but are
distinct from them; whereas, if the first elements could be described, and had a definition of
their own, they would be spoken of apart from all else. But none of these primeval elements
can be defined; they can only be named, for they have nothing but a name, and the things
which are compounded of them, as they are complex, are expressed by a combination of
names, for the combination of names is the essence of a definition. Thus, then, the elements or
letters are only objects of perception, and cannot be defined or known; but the syllables or
combinations of them are known and expressed, and are apprehended by true opinion.
When, therefore, any one forms the true opinion of anything without rational explanation, you
may say that his mind is truly exercised, but has no knowledge; for he who cannot give and
receive a reason for a thing, has no knowledge of that thing; but when he adds rational
explanation, then, he is perfected in knowledge and may be all that I have been denying of
him. Was that the form in which the dream appeared to you?
Recount and explain the significance of Socrates dream.
Socrates: And you allow and maintain that true opinion, combined with definition or rational
explanation, is knowledge?
Explain this sentence.
Socrates: Then may we assume, Theaetetus, that to-day, and in this casual manner, we have
found a truth which in former times many wise men have grown old and have not found?
Theaetetus: At any rate, Socrates, I am satisfied with the present statement.
Socrates: Which is probably correct-for how can there be knowledge apart from definition and
true opinion? And yet there is one point in what has been said which does not quite satisfy
Theaetetus: What was it?
Socrates: What might seem to be the most ingenious notion of all:-That the elements or letters are
unknown, but the combination or syllables known.
Theaetetus: And was that wrong?
Socrates: We shall soon know; for we have as hostages the instances which the author of the
argument himself used.
Theaetetus: What hostages?
Socrates: The letters, which are the clements; and the syllables, which are the combinations;-he
reasoned, did he not, from the letters of the alphabet?
Theaetetus: Yes; he did.
Socrates: Let us take them and put them to the quiz, or rather, quiz ourselves:-What was the way
in which we learned letters? and, first of all, are we right in saying that syllables have a
definition, but that letters have no definition?
Why do syllable have a definition but letters do not?
Theaetetus: I think so.
Socrates: I think so too; for, suppose that some one asks you to spell the first syllable of my
name:-Theaetetus, he says, what is SO?
Theaetetus: I should reply S and O.
Socrates: That is the definition which you would give of the syllable?
Theaetetus: I should.
Socrates: I wish that you would give me a similar definition of the S.
Theaetetus: But how can any one, Socrates, tell the elements of an element? I can only reply,
that S is a consonant, a mere noise, as of the tongue hissing; B, and most other letters, again,
are neither vowel-sounds nor noises. Thus letters may be most truly said to be undefined; for
even the most distinct of them, which are the seven vowels, have a sound only, but no
definition at all.
Socrates: Then, I suppose, my friend, that we have been so far right in our idea about knowledge?
Theaetetus: Yes; I think that we have.
Socrates: Well, but have we been right in maintaining that the syllables can be known, but not the
Theaetetus: I think so.
Socrates: And do we mean by a syllable two letters, or if there are more, all of them, or a single
idea which arises out of the combination of them?
Theaetetus: I should say that we mean all the letters.
Socrates: Take the case of the two letters S and O, which form the first syllable of my own name;
must not he who knows the syllable, know both of them?
Socrates: He knows, that is, the S and O?
Socrates: But can he be ignorant of either singly and yet know both together?
Theaetetus: Such a supposition, Socrates, is monstrous and unmeaning.
Socrates: But if he cannot know both without knowing each, then if he is ever to know the
syllable, he must know the letters first; and thus the fine theory has again taken wings and
Theaetetus: Yes, with wonderful celerity.
Socrates: Yes, we did not keep watch properly. Perhaps we ought to have maintained that a
syllable is not the letters, but rather one single idea framed out of them, having a separate
form distinct from them.
Theaetetus: Very true; and a more likely notion than the other.
Socrates: Take care; let us not be cowards and betray a great and imposing theory.
Theaetetus: No, indeed.
Socrates: Let us assume then, as we now say, that the syllable is a simple form arising out of the
several combinations of harmonious elements-of letters or of any other elements.
Theaetetus: Very good.
Socrates: And it must have no parts.
Socrates: Because that which has parts must be a whole of all the parts. Or would you say that a
whole, although formed out of the parts, is a single notion different from all the parts?
Theaetetus: I should.
Socrates: And would you say that all and the whole are the same, or different?
Theaetetus: I am not certain; but, as you like me to answer at once, I shall hazard the reply, that
they are different.
Socrates: I approve of your readiness, Theaetetus, but I must take time to think whether I equally
approve of your answer.
Theaetetus: Yes; the answer is the point.
Socrates: According to this new view, the whole is supposed to differ from all?
Socrates: Well, but is there any difference between all [in the plural] and the all [in the singular]?
Take the case of number:-When we say one, two, three, four, five, six; or when we say twice
three, or three times two, or four and two, or three and two and one, are we speaking of the
same or of different numbers?
Theaetetus: Of the same.
Socrates: That is of six?
Socrates: And in each form of expression we spoke of all the six?
Socrates: Again, in speaking of all [in the plural] is there not one thing which we express?
Theaetetus: Of course there is.
Socrates: And that is six?
Socrates: Then in predicating the word "all" of things measured by number, we predicate at the
same time a singular and a plural?
Theaetetus: Clearly we do.
Socrates: Again, the number of the acre and the acre are the same; are they not?
Socrates: And the number of the stadium in like manner is the stadium?
Socrates: And the army is the number of the army; and in all similar cases, the entire number of
anything is the entire thing?
Socrates: And the number of each is the parts of each?
Socrates: Then as many things as have parts are made up of parts?
Socrates: But all the parts are admitted to be the all, if the entire number is the all?
Socrates: Then the whole is not made up of parts, for it would be the all, if consisting of all the
Theaetetus: That is the inference.
Socrates: But is a part a part of anything but the whole?
Theaetetus: Yes, of the all.
Socrates: You make a valiant defence, Theaetetus. And yet is not the all that of which nothing is
Socrates: And is not a whole likewise that from which nothing is absent? but that from which
anything is absent is neither a whole nor all;-if wanting in anything, both equally lose their
entirety of nature.
Theaetetus: I now think that there is no difference between a whole and all.
Socrates: But were we not saying that when a thing has parts, all the parts will be a whole and all?
Socrates: Then, as I was saying before, must not the alternative be that either the syllable is not the
letters, and then the letters are not parts of the syllable, or that the syllable will be the same
with the letters, and will therefore be equally known with them?
Theaetetus: You are right.
Socrates: And, in order to avoid this, we suppose it to be different from them?
Socrates: But if letters are not parts of syllables, can you tell me of any other parts of syllables,
which are not letters?
Theaetetus: No, indeed, Socrates; for if I admit the existence of parts in a syllable, it would be
ridiculous in me to give up letters and seek for other parts.
Socrates: Quite true, Theaetetus, and therefore, according to our present view, a syllable must
surely be some indivisible form?
Socrates: But do you remember, my friend, that only a little while ago we admitted and approved
the statement, that of the first elements out of which all other things are compounded there
could be no definition, because each of them when taken by itself is uncompounded; nor can
one rightly attribute to them the words "being" or "this," because they are alien and
inappropriate words, and for this reason the letters or clements were indefinable and
Theaetetus: I remember.
Socrates: And is not this also the reason why they are simple and indivisible? I can see no other.
Theaetetus: No other reason can be given.
Socrates: Then is not the syllable in the same case as the elements or letters, if it has no parts and
is one form?
Theaetetus: To be sure.
Socrates: If, then, a syllable is a whole, and has many parts or letters, the letters as well as the
syllable must be intelligible and expressible, since all the parts are acknowledged to be the
same as the whole?
Socrates: But if it be one and indivisible, then the syllables and the letters are alike undefined and
unknown, and for the same reason?
Theaetetus: I cannot deny that.
Socrates: We cannot, therefore, agree in the opinion of him who says that the syllable can be
known and expressed, but not the letters.
Theaetetus: Certainly not; if we may trust the argument.
Socrates: Well, but will you not be equally inclined to, disagree with him, when you remember
your own experience in learning to read?
Theaetetus: What experience?
Socrates: Why, that in learning you were kept trying to distinguish the separate letters both by the
eye and by the car, in order that, when you heard them spoken or saw them written, you
might not be confused by their position.
Theaetetus: Very true.
Socrates: And is the education of the harp-player complete unless he can tell what string answers
to a particular note; the notes, as every one would allow, are the elements or letters of music?
Socrates: Then, if we argue from the letters and syllables which we know to other simples and
compounds, we shall say that the letters or simple clements as a class are much more
certainly known than the syllables, and much more indispensable to a perfect knowledge of
any subject; and if some one says that the syllable is known and the letter unknown, we shall
consider that either intentionally or unintentionally he is talking nonsense?
Why is it that the letter rather than the syllable truly known?
Socrates: And there might be given other proofs of this belief, if I am not mistaken. But do not let
us in looking for them lose sight of the question before us, which is the meaning of the
statement, that right opinion with rational definition or explanation is the most perfect form of
Theaetetus: We must not.
Socrates: Well, and what is the meaning of the term "explanation"? I think that we have a choice
of three meanings.
Theaetetus: What are they?
Socrates: In the first place, the meaning may be, manifesting one's thought by the voice with verbs
and nouns, imaging an opinion in the stream which flows from the lips, as in a mirror or water.
Does not explanation appear to be of this nature?
Theaetetus: Certainly; he who so manifests his thought, is said to explain himself.
Socrates: And every one who is not born deaf or dumb is able sooner or later to manifest what he
thinks of anything; and if so, all those who have a right opinion about anything will also have
right explanation; nor will right opinion be anywhere found to exist apart from knowledge.
Socrates: Let us not, therefore, hastily charge him who gave this account of knowledge with
uttering an unmeaning word; for perhaps he only intended to say, that when a person was
asked what was the nature of anything, he should be able to answer his questioner by giving
the clements of the thing.
Theaetetus: As for example, Socrates...?
Socrates: As, for example, when Hesiod says that a waggon is made up of a hundred planks.
Now, neither you nor I could describe all of them individually; but if any one asked what is a
waggon, we should be content to answer, that a waggon consists of wheels, axle, body, rims,
Socrates: And our opponent will probably laugh at us, just as he would if we professed to be
grammarians and to give a grammatical account of the name of Theaetetus, and yet could
only tell the syllables and not the letters of your name-that would be true opinion, and not
knowledge; for knowledge, as has been already remarked, is not attained until, combined
with true opinion, there is an enumeration of the elements out of which is composed.
Socrates: In the same general way, we might also have true opinion about a waggon; but he who
can describe its essence by an enumeration of the hundred planks, adds rational explanation
to true opinion, and instead of opinion has art and knowledge of the nature of a waggon, in
that he attains to the whole through the elements.
Explain the two ways in which the wagon may be known.
Theaetetus: And do. you not agree in that view, Socrates?
Socrates: If you do, my friend; but I want to know first, whether you admit the resolution of all
things into their elements to be a rational explanation of them, and the consideration of them in
syllables or larger combinations of them to be irrational-is this your view?
Socrates: Well, and do you conceive that a man has knowledge of any element who at one time
affirms and at another time denies that clement of something, or thinks that. the same thing is
composed of different elements at different times?
Theaetetus: Assuredly not.
Socrates: And do you not remember that in your case and in of others this often occurred in the
process of learning to read?
Theaetetus: You mean that I mistook the letters and misspelt the syllables?
Theaetetus: To be sure; I perfectly remember, and I am very far from supposing that they who
are in this condition, have knowledge.
Socrates: When a person, at the time of learning writes the name of Theaetetus, and thinks that he
ought to write and does write Th and e; but, again meaning to write the name of
Theododorus, thinks that he ought to write and does write T and e-can we suppose that he
knows the first syllables of your two names?
Theaetetus: We have already admitted that such a one has not yet attained knowledge.
Socrates: And in like manner be may enumerate without knowing them the second and third and
fourth syllables of your name?
Theaetetus: He may.
Socrates: And in that case, when he knows the order of the letters and can write them out
correctly, he has right opinion?
Socrates: But although we admit that he has right opinion, he will still be without knowledge?
Socrates: And yet he will have explanations, as well as right opinion, for he knew the order of the
letters when he wrote; and this we admit be explanation.
Socrates: Then, my friend, there is such a thing as right opinion united with definition or
explanation, which does not as yet attain to the exactness of knowledge.
Why does the letter/syllable analogy break down?
Theaetetus: It would seem so.
Socrates: And what we fancied to be a perfect definition of knowledge is a dream only. But
perhaps we had better not say so as yet, for were there not three explanations of knowledge,
one of which must, as we said, be adopted by him who maintains knowledge to be true
opinion combined with rational explanation? And very likely there may be found some one
who will not prefer this but the third.
Theaetetus: You are quite right; there is still one remaining. The first was the image or expression
of the mind in speech; the second, which has just been mentioned, is a way of reaching the
whole by an enumeration of the elements. But what is; the third definition?
Socrates: There is, further, the popular notion of telling the mark or sign of difference which
distinguishes the thing in question from all others.
Theaetetus: Can you give me any example of such a definition?
Socrates: As, for example, in the case of the sun, I think that you would be contented with the
statement that the sun is, the brighquiz of the heavenly bodies which revolve about the earth.
Socrates: Understand why:-the reason is, as I was just now saying, that if you get at the difference
and distinguishing characteristic of each thing, then, as many persons affirm, you will get at the
definition or explanation of it; but while you lay hold only of the common and not of the
characteristic notion, you will only have the definition of those things to which this common
Theaetetus: I understand you, and your account of definition is in my judgment correct.
Socrates: But he, who having right opinion about anything, can find out the difference which
distinguishes it from other things will know that of which before he had only an opinion.
Theaetetus: Yes; that is what we are maintaining.
Socrates: Nevertheless, Theaetetus, on a nearer view, I find myself quite disappointed; the
picture, which at a distance was not so bad, has now become altogether unintelligible.
Theaetetus: What do you mean?
Socrates: I will endeavour to explain: I will suppose myself to have true opinion of you, and if to
this I add your definition, then I have knowledge, but if not, opinion only.
Socrates: The definition was assumed to be the interpretation of your difference.
Socrates: But when I had only opinion, I had no conception of your distinguishing characteristics.
Theaetetus: I suppose not.
Socrates: Then I must have conceived of some general or common nature which no more
belonged to you than to another.
Socrates: Tell me, now-How in that case could I have formed a judgment of you any more than of
any one else? Suppose that I imagine Theaetetus to be a man who has nose, eyes, and
mouth, and every other member complete; how would that enable me to distinguish
Theaetetus from Theodorus, or from some outer barbarian?
Theaetetus: How could it?
Socrates: Or if I had further conceived of you, not only as having nose and eyes, but as having a
snub nose and prominent eyes, should I have any more notion of you than of myself and
others who resemble me?
Theaetetus: Certainly not.
Socrates: Surely I can have no conception of Theaetetus until your snub-nosedness has left an
impression on my mind different from the snub-nosedness of all others whom I have ever
seen, and until your other peculiarities have a like distinctness; and so when I meet you
tomorrow the right opinion will be re-called?
Theaetetus: Most true.
Socrates: Then right opinion implies the perception of differences?
Socrates: What, then, shall we say of adding reason or explanation to right opinion? If the meaning
is, that we should form an opinion of the way in which something differs from another thing,
the proposal is ridiculous.
Theaetetus: How so?
Socrates: We are supposed to acquire a right opinion of the differences which distinguish one
thing from another when we have already a right opinion of them, and so we go round and
round:-the revolution of the scytal, or pestle, or any other rotatory machine, in the same
circles, is as nothing compared with such a requirement; and we may be truly described as
the blind directing the blind; for to add those things which we already have, in order that we
may learn what we already think, is like a soul utterly benighted.
Theaetetus: Tell me; what were you going to say just now, when you asked the question?
Socrates: If, my boy, the argument, in speaking of adding the definition, had used the word to
"know," and not merely "have an opinion" of the difference, this which is the most promising
of all the definitions of knowledge would have come to a pretty end, for to know is surely to
Socrates: And so, when the question is asked, What is knowledge? this fair argument will answer
"Right opinion with knowledge,"-knowledge, that is, of difference, for this, as the said
argument maintains, is adding the definition.
Theaetetus: That seems to be true.
Socrates: But how utterly foolish, when we are asking what is knowledge, that the reply should
only be, right opinion with knowledge of difference or of anything! And so, Theaetetus,
knowledge is neither sensation nor true opinion, nor yet definition and explanation
accompanying and added to true opinion?
Theaetetus: I suppose not.
Socrates: And are you still in labour and travail, my dear friend, or have you brought all that you
have to say about knowledge to the birth?
Theaetetus: I am sure, Socrates, that you have elicited from me a good deal more than ever was
Socrates: And does not my art show that you have brought forth wind, and that the offspring of
your brain are not worth bringing up?
Theaetetus: Very true.
Socrates: But if, Theaetetus, you should ever conceive afresh, you will be all the better for the
present investigation, and if not, you will be soberer and humbler and gentler to other men,
and will be too modest to fancy that you know what you do not know. These are the limits of
my art; I can no further go, nor do I know aught of the things which great and famous men
know or have known in this or former ages. The office of a midwife I, like my mother, have
received from God; she delivered women, I deliver men; but they must be young and noble
And now I have to go to the porch of the King Archon, where I am to meet Meletus and his
indictment. To-morrow morning, Theodorus, I shall hope to see you again at this place.