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Theaetetus by Plato

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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 perception 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 percipient 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 I 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 no one.

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

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 new-born 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

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 overpowering 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 gymnasium.

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 or 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

SOCRATES: Then you and Theodorus mean to say that we must look at the
matter in some other way?

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.

THEAETETUS: Certainly.

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?

THEAETETUS: Certainly.

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

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.

THEAETETUS: Certainly.

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

THEAETETUS: Most true.

SOCRATES: Thus, then, the assertion that knowledge and perception are one,
involves a manifest impossibility?


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 (Lys.; Phaedo; Republic), 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 I must take up his
cause myself, and see justice done?

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 Theaetetus?

THEODORUS: To both of us, and let the younger answer; he will incur less
disgrace if he is discomfited.

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 inevitable

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.

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 him?

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 will 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 press 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. He 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, at least in their
own opinion.

THEODORUS: Certainly.

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.


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?

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 thousand others?

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 than true.

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.

THEODORUS: Certainly.

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?

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 one else?

THEODORUS: I think, Socrates, that we are running my old friend too hard.

SOCRATES: But I 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 themselves.

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 than
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.

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 offices--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 within reach.

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 tractable 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 some one 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 been 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

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 and
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 it not?

THEODORUS: Certainly it would.

SOCRATES: He ought not to speak of the name, but of the thing which is
contemplated under the name.


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 greatest 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 recognised, if
we put the question in reference to the whole class under which the good or
expedient falls. 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

THEODORUS: Certainly.

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 give 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 Ionia the sect makes rapid
strides; the disciples of Heracleitus are most energetic upholders of the

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 new-fangled
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. From 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 geometrical problem.

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
in 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 great?

THEODORUS: Nay, Socrates, not to examine thoroughly what the two parties
have to say would be quite intolerable.

SOCRATES: Then examine we must, since you, who were so reluctant to begin,
are so eager to proceed. The nature of motion appears to be the question
with which we begin. What do they mean when they say that all things are
in motion? Is there only one kind of motion, or, as I rather incline to
think, two? I should like to have your opinion upon this point in addition
to my own, that I may err, if I must err, in your company; tell me, then,
when a thing changes from one place to another, or goes round in the same
place, is not that what is called motion?


SOCRATES: Here then we have one kind of motion. But when a thing,
remaining on the same spot, grows old, or becomes black from being white,
or hard from being soft, or undergoes any other change, may not this be
properly called motion of another kind?

THEODORUS: I think so.

SOCRATES: Say rather that it must be so. Of motion then there are these
two kinds, 'change,' and 'motion in place.'

THEODORUS: You are right.

SOCRATES: And now, having made this distinction, let us address ourselves
to those who say that all is motion, and ask them whether all things
according to them have the two kinds of motion, and are changed as well as
move in place, or is one thing moved in both ways, and another in one only?

THEODORUS: Indeed, I do not know what to answer; but I think they would
say that all things are moved in both ways.

SOCRATES: Yes, comrade; for, if not, they would have to say that the same
things are in motion and at rest, and there would be no more truth in
saying that all things are in motion, than that all things are at rest.

THEODORUS: To be sure.

SOCRATES: And if they are to be in motion, and nothing is to be devoid of
motion, all things must always have every sort of motion?

THEODORUS: Most true.

SOCRATES: Consider a further point: did we not understand them to explain
the generation of heat, whiteness, or anything else, in some such manner as
the following:--were they not saying that each of them is moving between
the agent and the patient, together with a perception, and that the patient
ceases to be a perceiving power and becomes a percipient, and the agent a
quale instead of a quality? I suspect that quality may appear a strange
and uncouth term to you, and that you do not understand the abstract
expression. Then I will take concrete instances: I mean to say that the
producing power or agent becomes neither heat nor whiteness but hot and
white, and the like of other things. For I must repeat what I said before,
that neither the agent nor patient have any absolute existence, but when
they come together and generate sensations and their objects, the one
becomes a thing of a certain quality, and the other a percipient. You

THEODORUS: Of course.

SOCRATES: We may leave the details of their theory unexamined, but we must
not forget to ask them the only question with which we are concerned: Are
all things in motion and flux?

THEODORUS: Yes, they will reply.

SOCRATES: And they are moved in both those ways which we distinguished,
that is to say, they move in place and are also changed?

THEODORUS: Of course, if the motion is to be perfect.

SOCRATES: If they only moved in place and were not changed, we should be
able to say what is the nature of the things which are in motion and flux?


SOCRATES: But now, since not even white continues to flow white, and
whiteness itself is a flux or change which is passing into another colour,
and is never to be caught standing still, can the name of any colour be
rightly used at all?

THEODORUS: How is that possible, Socrates, either in the case of this or
of any other quality--if while we are using the word the object is escaping
in the flux?

SOCRATES: And what would you say of perceptions, such as sight and
hearing, or any other kind of perception? Is there any stopping in the act
of seeing and hearing?

THEODORUS: Certainly not, if all things are in motion.

SOCRATES: Then we must not speak of seeing any more than of not-seeing,
nor of any other perception more than of any non-perception, if all things
partake of every kind of motion?

THEODORUS: Certainly not.

SOCRATES: Yet perception is knowledge: so at least Theaetetus and I were

THEODORUS: Very true.

SOCRATES: Then when we were asked what is knowledge, we no more answered
what is knowledge than what is not knowledge?

THEODORUS: I suppose not.

SOCRATES: Here, then, is a fine result: we corrected our first answer in
our eagerness to prove that nothing is at rest. But if nothing is at rest,
every answer upon whatever subject is equally right: you may say that a
thing is or is not thus; or, if you prefer, 'becomes' thus; and if we say
'becomes,' we shall not then hamper them with words expressive of rest.

THEODORUS: Quite true.

SOCRATES: Yes, Theodorus, except in saying 'thus' and 'not thus.' But you
ought not to use the word 'thus,' for there is no motion in 'thus' or in
'not thus.' The maintainers of the doctrine have as yet no words in which
to express themselves, and must get a new language. I know of no word that
will suit them, except perhaps 'no how,' which is perfectly indefinite.

THEODORUS: Yes, that is a manner of speaking in which they will be quite
at home.

SOCRATES: And so, Theodorus, we have got rid of your friend without
assenting to his doctrine, that every man is the measure of all things--a
wise man only is a measure; neither can we allow that knowledge is
perception, certainly not on the hypothesis of a perpetual flux, unless
perchance our friend Theaetetus is able to convince us that it is.

THEODORUS: Very good, Socrates; and now that the argument about the
doctrine of Protagoras has been completed, I am absolved from answering;
for this was the agreement.

THEAETETUS: Not, Theodorus, until you and Socrates have discussed the
doctrine of those who say that all things are at rest, as you were

THEODORUS: You, Theaetetus, who are a young rogue, must not instigate your
elders to a breach of faith, but should prepare to answer Socrates in the
remainder of the argument.

THEAETETUS: Yes, if he wishes; but I would rather have heard about the
doctrine of rest.

THEODORUS: Invite Socrates to an argument--invite horsemen to the open
plain; do but ask him, and he will answer.

SOCRATES: Nevertheless, Theodorus, I am afraid that I shall not be able to
comply with the request of Theaetetus.

THEODORUS: Not comply! for what reason?

SOCRATES: My reason is that I have a kind of reverence; not so much for
Melissus and the others, who say that 'All is one and at rest,' as for the
great leader himself, Parmenides, venerable and awful, as in Homeric
language he may be called;--him I should be ashamed to approach in a spirit
unworthy of him. I met him when he was an old man, and I was a mere youth,
and he appeared to me to have a glorious depth of mind. And I am afraid
that we may not understand his words, and may be still further from
understanding his meaning; above all I fear that the nature of knowledge,
which is the main subject of our discussion, may be thrust out of sight by
the unbidden guests who will come pouring in upon our feast of discourse,
if we let them in--besides, the question which is now stirring is of
immense extent, and will be treated unfairly if only considered by the way;
or if treated adequately and at length, will put into the shade the other
question of knowledge. Neither the one nor the other can be allowed; but I
must try by my art of midwifery to deliver Theaetetus of his conceptions
about knowledge.

THEAETETUS: Very well; do so if you will.

SOCRATES: Then now, Theaetetus, take another view of the subject: you
answered that knowledge is perception?


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.'


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

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?

THEAETETUS: Certainly.

SOCRATES: And that both are two and each of them one?


SOCRATES: You can further observe whether they are like or unlike one

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

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

SOCRATES: You follow me excellently, Theaetetus; that is precisely what I
am asking.

THEAETETUS: Indeed, Socrates, I cannot answer; my only notion is, that
these, unlike objects of sense, have no separate organ, but that the mind,
by a power of her own, contemplates the universals in all things.

SOCRATES: You are a beauty, Theaetetus, and not ugly, as Theodorus was
saying; for he who utters the beautiful is himself beautiful and good. And
besides being beautiful, you have done me a kindness in releasing me from a
very long discussion, if you are clear that the soul views some things by
herself and others through the bodily organs. For that was my own opinion,
and I wanted you to agree with me.

THEAETETUS: I am quite clear.

SOCRATES: And to which class would you refer being or essence; for this,
of all our notions, is the most universal?

THEAETETUS: I should say, to that class which the soul aspires to know of

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?

THEAETETUS: Certainly.

SOCRATES: The simple sensations which reach the soul through the body are
given at birth to men and animals by nature, but their reflections on the
being and use of them are slowly and hardly gained, if they are ever
gained, by education and long experience.

THEAETETUS: Assuredly.

SOCRATES: And can a man attain truth who fails of attaining being?

THEAETETUS: Impossible.

SOCRATES: And can he who misses the truth of anything, have a knowledge of
that thing?

THEAETETUS: He cannot.

SOCRATES: Then knowledge does not consist in impressions of sense, but in
reasoning about them; in that only, and not in the mere impression, truth
and being can be attained?


SOCRATES: And would you call the two processes by the same name, when
there is so great a difference between them?

THEAETETUS: That would certainly not be right.

SOCRATES: And what name would you give to seeing, hearing, smelling, being
cold and being hot?

THEAETETUS: I should call all of them perceiving--what other name could be
given to them?

SOCRATES: Perception would be the collective name of them?

THEAETETUS: Certainly.

SOCRATES: Which, as we say, has no part in the attainment of truth any
more than of being?

THEAETETUS: Certainly not.

SOCRATES: And therefore not in science or knowledge?


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

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

THEAETETUS: To what are you alluding?

SOCRATES: There is a point which often troubles me, and is a great
perplexity to me, both in regard to myself and others. I cannot make out
the nature or origin of the mental experience to which I refer.

THEAETETUS: Pray what is it?

SOCRATES: How there can be false opinion--that difficulty still troubles
the eye of my mind; and I am uncertain whether I shall leave the question,
or begin over again in a new way.

THEAETETUS: Begin again, Socrates,--at least if you think that there is
the slightest necessity for doing so. Were not you and Theodorus just now
remarking very truly, that in discussions of this kind we may take our own

SOCRATES: You are quite right, and perhaps there will be no harm in
retracing our steps and beginning again. Better a little which is well
done, than a great deal imperfectly.

THEAETETUS: Certainly.

SOCRATES: Well, and what is the difficulty? Do we not speak of false
opinion, and say that one man holds a false and another a true opinion, as
though there were some natural distinction between them?

THEAETETUS: We certainly say so.

SOCRATES: All things and everything are either known or not known. I
leave out of view the intermediate conceptions of learning and forgetting,
because they have nothing to do with our present question.

THEAETETUS: There can be no doubt, Socrates, if you exclude these, that
there is no other alternative but knowing or not knowing a thing.

SOCRATES: That point being now determined, must we not say that he who has
an opinion, must have an opinion about something which he knows or does not


SOCRATES: He who knows, cannot but know; and he who does not know, cannot

THEAETETUS: Of course.

SOCRATES: What shall we say then? When a man has a false opinion does he
think that which he knows to be some other thing which he knows, and
knowing both, is he at the same time ignorant of both?

THEAETETUS: That, Socrates, is impossible.

SOCRATES: But perhaps he thinks of something which he does not know as
some other thing which he does not know; for example, he knows neither
Theaetetus nor Socrates, and yet he fancies that Theaetetus is Socrates, or
Socrates Theaetetus?

THEAETETUS: How can he?

SOCRATES: But surely he cannot suppose what he knows to be what he does
not know, or what he does not know to be what he knows?

THEAETETUS: That would be monstrous.

SOCRATES: Where, then, is false opinion? For if all things are either
known or unknown, there can be no opinion which is not comprehended under
this alternative, and so false opinion is excluded.

THEAETETUS: Most true.

SOCRATES: Suppose that we remove the question out of the sphere of knowing
or not knowing, into that of being and not-being.

THEAETETUS: What do you mean?

SOCRATES: May we not suspect the simple truth to be that he who thinks
about anything, that which is not, will necessarily think what is false,
whatever in other respects may be the state of his mind?

THEAETETUS: That, again, is not unlikely, Socrates.

SOCRATES: Then suppose some one to say to us, Theaetetus:--Is it possible
for any man to think that which is not, either as a self-existent substance
or as a predicate of something else? And suppose that we answer, 'Yes, he
can, when he thinks what is not true.'--That will be our answer?


SOCRATES: But is there any parallel to this?

THEAETETUS: What do you mean?

SOCRATES: Can a man see something and yet see nothing?

THEAETETUS: Impossible.

SOCRATES: But if he sees any one thing, he sees something that exists. Do
you suppose that what is one is ever to be found among non-existing things?


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?

THEAETETUS: Certainly.

SOCRATES: And does not he who thinks some one thing, think something which


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?

THEAETETUS: Obviously.

SOCRATES: Then no one can think that which is not, either as a self-
existent substance or as a predicate of something else?

THEAETETUS: Clearly not.

SOCRATES: Then to think falsely is different from thinking that which is

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 me.

THEAETETUS: What makes you say so?

SOCRATES: You think, if I am not mistaken, that your 'truly false' is safe
from censure, and that I shall never ask whether there can be a swift which
is slow, or a heavy which is light, or any other self-contradictory thing,
which works, not according to its own nature, but according to that of its
opposite. But I will not insist upon this, for I do not wish needlessly to
discourage you. And so you are satisfied that false opinion is heterodoxy,
or the thought of something else?


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?

THEAETETUS: Certainly.

SOCRATES: Either together or in succession?

THEAETETUS: Very good.

SOCRATES: And do you mean by conceiving, the same which I mean?

THEAETETUS: What is that?

SOCRATES: I mean the conversation which the soul holds with herself in
considering of anything. I speak of what I scarcely understand; but the
soul when thinking appears to me to be just talking--asking questions of
herself and answering them, affirming and denying. And when she has
arrived at a decision, either gradually or by a sudden impulse, and has at
last agreed, and does not doubt, this is called her opinion. I say, then,
that to form an opinion is to speak, and opinion is a word spoken,--I mean,
to oneself and in silence, not aloud or to another: What think you?


SOCRATES: Then when any one thinks of one thing as another, he is saying
to himself that one thing is another?


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 (Both words in Greek are
called eteron: compare Parmen.; Euthyd.)). 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 other?


SOCRATES: Neither, if he has one of them only in his mind and not the
other, can he think that one is the other?

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 in us.


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--then 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 tested. Tell me, then, whether I am right in
saying that you may learn a thing which at one time you did not know?

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.


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 not know.

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.

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.

THEAETETUS: I understand you less than ever now.

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 not right?

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?


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 fail 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.

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

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.

THEAETETUS: Undoubtedly.

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


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.

THEAETETUS: No man, Socrates, can say anything truer than that.

SOCRATES: Then now we may admit the existence of false opinion in us?

THEAETETUS: Certainly.

SOCRATES: And of true opinion also?


SOCRATES: We have at length satisfactorily proven beyond a doubt there are
these two sorts of opinion?

THEAETETUS: Undoubtedly.

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: 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, can 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.

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.

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