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Theaetetus by Plato

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THEAETETUS: Most true.

SOCRATES: Then false opinion cannot be explained as a confusion of thought
and sense, for in that case we could not have been mistaken about pure
conceptions of thought; and thus we are obliged to say, either that false
opinion does not exist, or that a man may not know that which he knows;--
which alternative do you prefer?

THEAETETUS: It is hard to determine, Socrates.

SOCRATES: And yet the argument will scarcely admit of both. But, as we
are at our wits' end, suppose that we do a shameless thing?

THEAETETUS: What is it?

SOCRATES: Let us attempt to explain the verb 'to know.'

THEAETETUS: And why should that be shameless?

SOCRATES: You seem not to be aware that the whole of our discussion from
the very beginning has been a search after knowledge, of which we are
assumed not to know the nature.

THEAETETUS: Nay, but I am well aware.

SOCRATES: And is it not shameless when we do not know what knowledge is,
to be explaining the verb 'to know'? The truth is, Theaetetus, that we
have long been infected with logical impurity. Thousands of times have we
repeated the words 'we know,' and 'do not know,' and 'we have or have not
science or knowledge,' as if we could understand what we are saying to one
another, so long as we remain ignorant about knowledge; and at this moment
we are using the words 'we understand,' 'we are ignorant,' as though we
could still employ them when deprived of knowledge or science.

THEAETETUS: But if you avoid these expressions, Socrates, how will you
ever argue at all?

SOCRATES: I could not, being the man I am. The case would be different if
I were a true hero of dialectic: and O that such an one were present! for
he would have told us to avoid the use of these terms; at the same time he
would not have spared in you and me the faults which I have noted. But,
seeing that we are no great wits, shall I venture to say what knowing is?
for I think that the attempt may be worth making.

THEAETETUS: Then by all means venture, and no one shall find fault with
you for using the forbidden terms.

SOCRATES: You have heard the common explanation of the verb 'to know'?

THEAETETUS: I think so, but I do not remember it at the moment.

SOCRATES: They explain the word 'to know' as meaning 'to have knowledge.'


SOCRATES: I should like to make a slight change, and say 'to possess'

THEAETETUS: How do the two expressions differ?

SOCRATES: Perhaps there may be no difference; but still I should like you
to hear my view, that you may help me to test it.

THEAETETUS: I will, if I can.

SOCRATES: I should distinguish 'having' from 'possessing': for example, a
man may buy and keep under his control a garment which he does not wear;
and then we should say, not that he has, but that he possesses the garment.

THEAETETUS: It would be the correct expression.

SOCRATES: Well, may not a man 'possess' and yet not 'have' knowledge in
the sense of which I am speaking? As you may suppose a man to have caught
wild birds--doves or any other birds--and to be keeping them in an aviary
which he has constructed at home; we might say of him in one sense, that he
always has them because he possesses them, might we not?


SOCRATES: And yet, in another sense, he has none of them; but they are in
his power, and he has got them under his hand in an enclosure of his own,
and can take and have them whenever he likes;--he can catch any which he
likes, and let the bird go again, and he may do so as often as he pleases.


SOCRATES: Once more, then, as in what preceded we made a sort of waxen
figment in the mind, so let us now suppose that in the mind of each man
there is an aviary of all sorts of birds--some flocking together apart from
the rest, others in small groups, others solitary, flying anywhere and

THEAETETUS: Let us imagine such an aviary--and what is to follow?

SOCRATES: We may suppose that the birds are kinds of knowledge, and that
when we were children, this receptacle was empty; whenever a man has gotten
and detained in the enclosure a kind of knowledge, he may be said to have
learned or discovered the thing which is the subject of the knowledge: and
this is to know.


SOCRATES: And further, when any one wishes to catch any of these
knowledges or sciences, and having taken, to hold it, and again to let them
go, how will he express himself?--will he describe the 'catching' of them
and the original 'possession' in the same words? I will make my meaning
clearer by an example:--You admit that there is an art of arithmetic?

THEAETETUS: To be sure.

SOCRATES: Conceive this under the form of a hunt after the science of odd
and even in general.


SOCRATES: Having the use of the art, the arithmetician, if I am not
mistaken, has the conceptions of number under his hand, and can transmit
them to another.


SOCRATES: And when transmitting them he may be said to teach them, and
when receiving to learn them, and when receiving to learn them, and when
having them in possession in the aforesaid aviary he may be said to know


SOCRATES: Attend to what follows: must not the perfect arithmetician know
all numbers, for he has the science of all numbers in his mind?


SOCRATES: And he can reckon abstract numbers in his head, or things about
him which are numerable?

THEAETETUS: Of course he can.

SOCRATES: And to reckon is simply to consider how much such and such a
number amounts to?

THEAETETUS: Very true.

SOCRATES: And so he appears to be searching into something which he knows,
as if he did not know it, for we have already admitted that he knows all
numbers;--you have heard these perplexing questions raised?


SOCRATES: May we not pursue the image of the doves, and say that the chase
after knowledge is of two kinds? one kind is prior to possession and for
the sake of possession, and the other for the sake of taking and holding in
the hands that which is possessed already. And thus, when a man has
learned and known something long ago, he may resume and get hold of the
knowledge which he has long possessed, but has not at hand in his mind.


SOCRATES: That was my reason for asking how we ought to speak when an
arithmetician sets about numbering, or a grammarian about reading? Shall
we say, that although he knows, he comes back to himself to learn what he
already knows?

THEAETETUS: It would be too absurd, Socrates.

SOCRATES: Shall we say then that he is going to read or number what he
does not know, although we have admitted that he knows all letters and all

THEAETETUS: That, again, would be an absurdity.

SOCRATES: Then shall we say that about names we care nothing?--any one may
twist and turn the words 'knowing' and 'learning' in any way which he
likes, but since we have determined that the possession of knowledge is not
the having or using it, we do assert that a man cannot not possess that
which he possesses; and, therefore, in no case can a man not know that
which he knows, but he may get a false opinion about it; for he may have
the knowledge, not of this particular thing, but of some other;--when the
various numbers and forms of knowledge are flying about in the aviary, and
wishing to capture a certain sort of knowledge out of the general store, he
takes the wrong one by mistake, that is to say, when he thought eleven to
be twelve, he got hold of the ring-dove which he had in his mind, when he
wanted the pigeon.

THEAETETUS: A very rational explanation.

SOCRATES: But when he catches the one which he wants, then he is not
deceived, and has an opinion of what is, and thus false and true opinion
may exist, and the difficulties which were previously raised disappear. I
dare say that you agree with me, do you not?


SOCRATES: And so we are rid of the difficulty of a man's not knowing what
he knows, for we are not driven to the inference that he does not possess
what he possesses, whether he be or be not deceived. And yet I fear that a
greater difficulty is looking in at the window.

THEAETETUS: What is it?

SOCRATES: How can the exchange of one knowledge for another ever become
false opinion?

THEAETETUS: What do you mean?

SOCRATES: In the first place, how can a man who has the knowledge of
anything be ignorant of that which he knows, not by reason of ignorance,
but by reason of his own knowledge? And, again, is it not an extreme
absurdity that he should suppose another thing to be this, and this to be
another thing;--that, having knowledge present with him in his mind, he
should still know nothing and be ignorant of all things?--you might as well
argue that ignorance may make a man know, and blindness make him see, as
that knowledge can make him ignorant.

THEAETETUS: Perhaps, Socrates, we may have been wrong in making only forms
of knowledge our birds: whereas there ought to have been forms of
ignorance as well, flying about together in the mind, and then he who
sought to take one of them might sometimes catch a form of knowledge, and
sometimes a form of ignorance; and thus he would have a false opinion from
ignorance, but a true one from knowledge, about the same thing.

SOCRATES: I cannot help praising you, Theaetetus, and yet I must beg you
to reconsider your words. Let us grant what you say--then, according to
you, he who takes ignorance will have a false opinion--am I right?


SOCRATES: He will certainly not think that he has a false opinion?

THEAETETUS: Of course not.

SOCRATES: He will think that his opinion is true, and he will fancy that
he knows the things about which he has been deceived?

THEAETETUS: Certainly.

SOCRATES: Then he will think that he has captured knowledge and not


SOCRATES: And thus, after going a long way round, we are once more face to
face with our original difficulty. The hero of dialectic will retort upon
us:--'O my excellent friends, he will say, laughing, if a man knows the
form of ignorance and the form of knowledge, can he think that one of them
which he knows is the other which he knows? or, if he knows neither of
them, can he think that the one which he knows not is another which he
knows not? or, if he knows one and not the other, can he think the one
which he knows to be the one which he does not know? or the one which he
does not know to be the one which he knows? or will you tell me that there
are other forms of knowledge which distinguish the right and wrong birds,
and which the owner keeps in some other aviaries or graven on waxen blocks
according to your foolish images, and which he may be said to know while he
possesses them, even though he have them not at hand in his mind? And
thus, in a perpetual circle, you will be compelled to go round and round,
and you will make no progress.' What are we to say in reply, Theaetetus?

THEAETETUS: Indeed, Socrates, I do not know what we are to say.

SOCRATES: Are not his reproaches just, and does not the argument truly
show that we are wrong in seeking for false opinion until we know what
knowledge is; that must be first ascertained; then, the nature of false

THEAETETUS: I cannot but agree with you, Socrates, so far as we have yet

SOCRATES: Then, once more, what shall we say that knowledge is?--for we
are not going to lose heart as yet.

THEAETETUS: Certainly, I shall not lose heart, if you do not.

SOCRATES: What definition will be most consistent with our former views?

THEAETETUS: I cannot think of any but our old one, Socrates.

SOCRATES: What was it?

THEAETETUS: Knowledge was said by us to be true opinion; and true opinion
is surely unerring, and the results which follow from it are all noble and

SOCRATES: He who led the way into the river, Theaetetus, said 'The
experiment will show;' and perhaps if we go forward in the search, we may
stumble upon the thing which we are looking for; but if we stay where we
are, nothing will come to light.

THEAETETUS: Very true; let us go forward and try.

SOCRATES: The trail soon comes to an end, for a whole profession is
against us.

THEAETETUS: How is that, and what profession do you mean?

SOCRATES: The profession of the great wise ones who are called orators and
lawyers; for these persuade men by their art and make them think whatever
they like, but they do not teach them. Do you imagine that there are any
teachers in the world so clever as to be able to convince others of the
truth about acts of robbery or violence, of which they were not eye-
witnesses, while a little water is flowing in the clepsydra?

THEAETETUS: Certainly not, they can only persuade them.

SOCRATES: And would you not say that persuading them is making them have
an opinion?

THEAETETUS: To be sure.

SOCRATES: When, therefore, judges are justly persuaded about matters which
you can know only by seeing them, and not in any other way, and when thus
judging of them from report they attain a true opinion about them, they
judge without knowledge, and yet are rightly persuaded, if they have judged

THEAETETUS: Certainly.

SOCRATES: And yet, O my friend, if true opinion in law courts and
knowledge are the same, the perfect judge could not have judged rightly
without knowledge; and therefore I must infer that they are not the same.

THEAETETUS: That is a distinction, Socrates, which I have heard made by
some one else, but I had forgotten it. He said that true opinion, combined
with reason, was knowledge, but that the opinion which had no reason was
out of the sphere of knowledge; and that things of which there is no
rational account are not knowable--such was the singular expression which
he used--and that things which have a reason or explanation are knowable.

SOCRATES: Excellent; but then, how did he distinguish between things which
are and are not 'knowable'? I wish that you would repeat to me what he
said, and then I shall know whether you and I have heard the same tale.

THEAETETUS: I do not know whether I can recall it; but if another person
would tell me, I think that I could follow him.

SOCRATES: Let me give you, then, a dream in return for a dream:--Methought
that I too had a dream, and I heard in my dream that the primeval letters
or elements out of which you and I and all other things are compounded,
have no reason or explanation; you can only name them, but no predicate can
be either affirmed or denied of them, for in the one case existence, in the
other non-existence is already implied, neither of which must be added, if
you mean to speak of this or that thing by itself alone. It should not be
called itself, or that, or each, or alone, or this, or the like; for these
go about everywhere and are applied to all things, but are distinct from
them; whereas, if the first elements could be described, and had a
definition of their own, they would be spoken of apart from all else. But
none of these primeval elements can be defined; they can only be named, for
they have nothing but a name, and the things which are compounded of them,
as they are complex, are expressed by a combination of names, for the
combination of names is the essence of a definition. Thus, then, the
elements or letters are only objects of perception, and cannot be defined
or known; but the syllables or combinations of them are known and
expressed, and are apprehended by true opinion. When, therefore, any one
forms the true opinion of anything without rational explanation, you may
say that his mind is truly exercised, but has no knowledge; for he who
cannot give and receive a reason for a thing, has no knowledge of that
thing; but when he adds rational explanation, then, he is perfected in
knowledge and may be all that I have been denying of him. Was that the
form in which the dream appeared to you?

THEAETETUS: Precisely.

SOCRATES: And you allow and maintain that true opinion, combined with
definition or rational explanation, is knowledge?


SOCRATES: Then may we assume, Theaetetus, that to-day, and in this casual
manner, we have found a truth which in former times many wise men have
grown old and have not found?

THEAETETUS: At any rate, Socrates, I am satisfied with the present

SOCRATES: Which is probably correct--for how can there be knowledge apart
from definition and true opinion? And yet there is one point in what has
been said which does not quite satisfy me.

THEAETETUS: What was it?

SOCRATES: What might seem to be the most ingenious notion of all:--That
the elements or letters are unknown, but the combination or syllables

THEAETETUS: And was that wrong?

SOCRATES: We shall soon know; for we have as hostages the instances which
the author of the argument himself used.

THEAETETUS: What hostages?

SOCRATES: The letters, which are the clements; and the syllables, which
are the combinations;--he reasoned, did he not, from the letters of the

THEAETETUS: Yes; he did.

SOCRATES: Let us take them and put them to the test, or rather, test
ourselves:--What was the way in which we learned letters? and, first of
all, are we right in saying that syllables have a definition, but that
letters have no definition?

THEAETETUS: I think so.

SOCRATES: I think so too; for, suppose that some one asks you to spell the
first syllable of my name:--Theaetetus, he says, what is SO?

THEAETETUS: I should reply S and O.

SOCRATES: That is the definition which you would give of the syllable?


SOCRATES: I wish that you would give me a similar definition of the S.

THEAETETUS: But how can any one, Socrates, tell the elements of an
element? I can only reply, that S is a consonant, a mere noise, as of the
tongue hissing; B, and most other letters, again, are neither vowel-sounds
nor noises. Thus letters may be most truly said to be undefined; for even
the most distinct of them, which are the seven vowels, have a sound only,
but no definition at all.

SOCRATES: Then, I suppose, my friend, that we have been so far right in
our idea about knowledge?

THEAETETUS: Yes; I think that we have.

SOCRATES: Well, but have we been right in maintaining that the syllables
can be known, but not the letters?

THEAETETUS: I think so.

SOCRATES: And do we mean by a syllable two letters, or if there are more,
all of them, or a single idea which arises out of the combination of them?

THEAETETUS: I should say that we mean all the letters.

SOCRATES: Take the case of the two letters S and O, which form the first
syllable of my own name; must not he who knows the syllable, know both of

THEAETETUS: Certainly.

SOCRATES: He knows, that is, the S and O?


SOCRATES: But can he be ignorant of either singly and yet know both

THEAETETUS: Such a supposition, Socrates, is monstrous and unmeaning.

SOCRATES: But if he cannot know both without knowing each, then if he is
ever to know the syllable, he must know the letters first; and thus the
fine theory has again taken wings and departed.

THEAETETUS: Yes, with wonderful celerity.

SOCRATES: Yes, we did not keep watch properly. Perhaps we ought to have
maintained that a syllable is not the letters, but rather one single idea
framed out of them, having a separate form distinct from them.

THEAETETUS: Very true; and a more likely notion than the other.

SOCRATES: Take care; let us not be cowards and betray a great and imposing

THEAETETUS: No, indeed.

SOCRATES: Let us assume then, as we now say, that the syllable is a simple
form arising out of the several combinations of harmonious elements--of
letters or of any other elements.

THEAETETUS: Very good.

SOCRATES: And it must have no parts.


SOCRATES: Because that which has parts must be a whole of all the parts.
Or would you say that a whole, although formed out of the parts, is a
single notion different from all the parts?


SOCRATES: And would you say that all and the whole are the same, or

THEAETETUS: I am not certain; but, as you like me to answer at once, I
shall hazard the reply, that they are different.

SOCRATES: I approve of your readiness, Theaetetus, but I must take time to
think whether I equally approve of your answer.

THEAETETUS: Yes; the answer is the point.

SOCRATES: According to this new view, the whole is supposed to differ from


SOCRATES: Well, but is there any difference between all (in the plural)
and the all (in the singular)? Take the case of number:--When we say one,
two, three, four, five, six; or when we say twice three, or three times
two, or four and two, or three and two and one, are we speaking of the same
or of different numbers?

THEAETETUS: Of the same.

SOCRATES: That is of six?


SOCRATES: And in each form of expression we spoke of all the six?


SOCRATES: Again, in speaking of all (in the plural) is there not one thing
which we express?

THEAETETUS: Of course there is.

SOCRATES: And that is six?


SOCRATES: Then in predicating the word 'all' of things measured by number,
we predicate at the same time a singular and a plural?

THEAETETUS: Clearly we do.

SOCRATES: Again, the number of the acre and the acre are the same; are
they not?


SOCRATES: And the number of the stadium in like manner is the stadium?


SOCRATES: And the army is the number of the army; and in all similar
cases, the entire number of anything is the entire thing?


SOCRATES: And the number of each is the parts of each?


SOCRATES: Then as many things as have parts are made up of parts?


SOCRATES: But all the parts are admitted to be the all, if the entire
number is the all?


SOCRATES: Then the whole is not made up of parts, for it would be the all,
if consisting of all the parts?

THEAETETUS: That is the inference.

SOCRATES: But is a part a part of anything but the whole?

THEAETETUS: Yes, of the all.

SOCRATES: You make a valiant defence, Theaetetus. And yet is not the all
that of which nothing is wanting?

THEAETETUS: Certainly.

SOCRATES: And is not a whole likewise that from which nothing is absent?
but that from which anything is absent is neither a whole nor all;--if
wanting in anything, both equally lose their entirety of nature.

THEAETETUS: I now think that there is no difference between a whole and

SOCRATES: But were we not saying that when a thing has parts, all the
parts will be a whole and all?

THEAETETUS: Certainly.

SOCRATES: Then, as I was saying before, must not the alternative be that
either the syllable is not the letters, and then the letters are not parts
of the syllable, or that the syllable will be the same with the letters,
and will therefore be equally known with them?

THEAETETUS: You are right.

SOCRATES: And, in order to avoid this, we suppose it to be different from


SOCRATES: But if letters are not parts of syllables, can you tell me of
any other parts of syllables, which are not letters?

THEAETETUS: No, indeed, Socrates; for if I admit the existence of parts in
a syllable, it would be ridiculous in me to give up letters and seek for
other parts.

SOCRATES: Quite true, Theaetetus, and therefore, according to our present
view, a syllable must surely be some indivisible form?


SOCRATES: But do you remember, my friend, that only a little while ago we
admitted and approved the statement, that of the first elements out of
which all other things are compounded there could be no definition, because
each of them when taken by itself is uncompounded; nor can one rightly
attribute to them the words 'being' or 'this,' because they are alien and
inappropriate words, and for this reason the letters or elements were
indefinable and unknown?

THEAETETUS: I remember.

SOCRATES: And is not this also the reason why they are simple and
indivisible? I can see no other.

THEAETETUS: No other reason can be given.

SOCRATES: Then is not the syllable in the same case as the elements or
letters, if it has no parts and is one form?

THEAETETUS: To be sure.

SOCRATES: If, then, a syllable is a whole, and has many parts or letters,
the letters as well as the syllable must be intelligible and expressible,
since all the parts are acknowledged to be the same as the whole?


SOCRATES: But if it be one and indivisible, then the syllables and the
letters are alike undefined and unknown, and for the same reason?

THEAETETUS: I cannot deny that.

SOCRATES: We cannot, therefore, agree in the opinion of him who says that
the syllable can be known and expressed, but not the letters.

THEAETETUS: Certainly not; if we may trust the argument.

SOCRATES: Well, but will you not be equally inclined to disagree with him,
when you remember your own experience in learning to read?

THEAETETUS: What experience?

SOCRATES: Why, that in learning you were kept trying to distinguish the
separate letters both by the eye and by the ear, in order that, when you
heard them spoken or saw them written, you might not be confused by their

THEAETETUS: Very true.

SOCRATES: And is the education of the harp-player complete unless he can
tell what string answers to a particular note; the notes, as every one
would allow, are the elements or letters of music?


SOCRATES: Then, if we argue from the letters and syllables which we know
to other simples and compounds, we shall say that the letters or simple
elements as a class are much more certainly known than the syllables, and
much more indispensable to a perfect knowledge of any subject; and if some
one says that the syllable is known and the letter unknown, we shall
consider that either intentionally or unintentionally he is talking


SOCRATES: And there might be given other proofs of this belief, if I am
not mistaken. But do not let us in looking for them lose sight of the
question before us, which is the meaning of the statement, that right
opinion with rational definition or explanation is the most perfect form of

THEAETETUS: We must not.

SOCRATES: Well, and what is the meaning of the term 'explanation'? I
think that we have a choice of three meanings.

THEAETETUS: What are they?

SOCRATES: In the first place, the meaning may be, manifesting one's
thought by the voice with verbs and nouns, imaging an opinion in the stream
which flows from the lips, as in a mirror or water. Does not explanation
appear to be of this nature?

THEAETETUS: Certainly; he who so manifests his thought, is said to explain

SOCRATES: And every one who is not born deaf or dumb is able sooner or
later to manifest what he thinks of anything; and if so, all those who have
a right opinion about anything will also have right explanation; nor will
right opinion be anywhere found to exist apart from knowledge.


SOCRATES: Let us not, therefore, hastily charge him who gave this account
of knowledge with uttering an unmeaning word; for perhaps he only intended
to say, that when a person was asked what was the nature of anything, he
should be able to answer his questioner by giving the elements of the

THEAETETUS: As for example, Socrates...?

SOCRATES: As, for example, when Hesiod says that a waggon is made up of a
hundred planks. Now, neither you nor I could describe all of them
individually; but if any one asked what is a waggon, we should be content
to answer, that a waggon consists of wheels, axle, body, rims, yoke.

THEAETETUS: Certainly.

SOCRATES: And our opponent will probably laugh at us, just as he would if
we professed to be grammarians and to give a grammatical account of the
name of Theaetetus, and yet could only tell the syllables and not the
letters of your name--that would be true opinion, and not knowledge; for
knowledge, as has been already remarked, is not attained until, combined
with true opinion, there is an enumeration of the elements out of which
anything is composed.


SOCRATES: In the same general way, we might also have true opinion about a
waggon; but he who can describe its essence by an enumeration of the
hundred planks, adds rational explanation to true opinion, and instead of
opinion has art and knowledge of the nature of a waggon, in that he attains
to the whole through the elements.

THEAETETUS: And do you not agree in that view, Socrates?

SOCRATES: If you do, my friend; but I want to know first, whether you
admit the resolution of all things into their elements to be a rational
explanation of them, and the consideration of them in syllables or larger
combinations of them to be irrational--is this your view?

THEAETETUS: Precisely.

SOCRATES: Well, and do you conceive that a man has knowledge of any
element who at one time affirms and at another time denies that element of
something, or thinks that the same thing is composed of different elements
at different times?

THEAETETUS: Assuredly not.

SOCRATES: And do you not remember that in your case and in that of others
this often occurred in the process of learning to read?

THEAETETUS: You mean that I mistook the letters and misspelt the


THEAETETUS: To be sure; I perfectly remember, and I am very far from
supposing that they who are in this condition have knowledge.

SOCRATES: When a person at the time of learning writes the name of
Theaetetus, and thinks that he ought to write and does write Th and e; but,
again, meaning to write the name of Theododorus, thinks that he ought to
write and does write T and e--can we suppose that he knows the first
syllables of your two names?

THEAETETUS: We have already admitted that such a one has not yet attained

SOCRATES: And in like manner be may enumerate without knowing them the
second and third and fourth syllables of your name?


SOCRATES: And in that case, when he knows the order of the letters and can
write them out correctly, he has right opinion?


SOCRATES: But although we admit that he has right opinion, he will still
be without knowledge?


SOCRATES: And yet he will have explanation, as well as right opinion, for
he knew the order of the letters when he wrote; and this we admit to be


SOCRATES: Then, my friend, there is such a thing as right opinion united
with definition or explanation, which does not as yet attain to the
exactness of knowledge.

THEAETETUS: It would seem so.

SOCRATES: And what we fancied to be a perfect definition of knowledge is a
dream only. But perhaps we had better not say so as yet, for were there
not three explanations of knowledge, one of which must, as we said, be
adopted by him who maintains knowledge to be true opinion combined with
rational explanation? And very likely there may be found some one who will
not prefer this but the third.

THEAETETUS: You are quite right; there is still one remaining. The first
was the image or expression of the mind in speech; the second, which has
just been mentioned, is a way of reaching the whole by an enumeration of
the elements. But what is the third definition?

SOCRATES: There is, further, the popular notion of telling the mark or
sign of difference which distinguishes the thing in question from all

THEAETETUS: Can you give me any example of such a definition?

SOCRATES: As, for example, in the case of the sun, I think that you would
be contented with the statement that the sun is the brightest of the
heavenly bodies which revolve about the earth.

THEAETETUS: Certainly.

SOCRATES: Understand why:--the reason is, as I was just now saying, that
if you get at the difference and distinguishing characteristic of each
thing, then, as many persons affirm, you will get at the definition or
explanation of it; but while you lay hold only of the common and not of the
characteristic notion, you will only have the definition of those things to
which this common quality belongs.

THEAETETUS: I understand you, and your account of definition is in my
judgment correct.

SOCRATES: But he, who having right opinion about anything, can find out
the difference which distinguishes it from other things will know that of
which before he had only an opinion.

THEAETETUS: Yes; that is what we are maintaining.

SOCRATES: Nevertheless, Theaetetus, on a nearer view, I find myself quite
disappointed; the picture, which at a distance was not so bad, has now
become altogether unintelligible.

THEAETETUS: What do you mean?

SOCRATES: I will endeavour to explain: I will suppose myself to have true
opinion of you, and if to this I add your definition, then I have
knowledge, but if not, opinion only.


SOCRATES: The definition was assumed to be the interpretation of your


SOCRATES: But when I had only opinion, I had no conception of your
distinguishing characteristics.

THEAETETUS: I suppose not.

SOCRATES: Then I must have conceived of some general or common nature
which no more belonged to you than to another.


SOCRATES: Tell me, now--How in that case could I have formed a judgment of
you any more than of any one else? Suppose that I imagine Theaetetus to be
a man who has nose, eyes, and mouth, and every other member complete; how
would that enable me to distinguish Theaetetus from Theodorus, or from some
outer barbarian?

THEAETETUS: How could it?

SOCRATES: Or if I had further conceived of you, not only as having nose
and eyes, but as having a snub nose and prominent eyes, should I have any
more notion of you than of myself and others who resemble me?

THEAETETUS: Certainly not.

SOCRATES: Surely I can have no conception of Theaetetus until your snub-
nosedness has left an impression on my mind different from the snub-
nosedness of all others whom I have ever seen, and until your other
peculiarities have a like distinctness; and so when I meet you to-morrow
the right opinion will be re-called?

THEAETETUS: Most true.

SOCRATES: Then right opinion implies the perception of differences?


SOCRATES: What, then, shall we say of adding reason or explanation to
right opinion? If the meaning is, that we should form an opinion of the
way in which something differs from another thing, the proposal is


SOCRATES: We are supposed to acquire a right opinion of the differences
which distinguish one thing from another when we have already a right
opinion of them, and so we go round and round:--the revolution of the
scytal, or pestle, or any other rotatory machine, in the same circles, is
as nothing compared with such a requirement; and we may be truly described
as the blind directing the blind; for to add those things which we already
have, in order that we may learn what we already think, is like a soul
utterly benighted.

THEAETETUS: Tell me; what were you going to say just now, when you asked
the question?

SOCRATES: If, my boy, the argument, in speaking of adding the definition,
had used the word to 'know,' and not merely 'have an opinion' of the
difference, this which is the most promising of all the definitions of
knowledge would have come to a pretty end, for to know is surely to acquire


SOCRATES: And so, when the question is asked, What is knowledge? this fair
argument will answer 'Right opinion with knowledge,'--knowledge, that is,
of difference, for this, as the said argument maintains, is adding the

THEAETETUS: That seems to be true.

SOCRATES: But how utterly foolish, when we are asking what is knowledge,
that the reply should only be, right opinion with knowledge of difference
or of anything! And so, Theaetetus, knowledge is neither sensation nor
true opinion, nor yet definition and explanation accompanying and added to
true opinion?

THEAETETUS: I suppose not.

SOCRATES: And are you still in labour and travail, my dear friend, or have
you brought all that you have to say about knowledge to the birth?

THEAETETUS: I am sure, Socrates, that you have elicited from me a good
deal more than ever was in me.

SOCRATES: And does not my art show that you have brought forth wind, and
that the offspring of your brain are not worth bringing up?

THEAETETUS: Very true.

SOCRATES: But if, Theaetetus, you should ever conceive afresh, you will be
all the better for the present investigation, and if not, you will be
soberer and humbler and gentler to other men, and will be too modest to
fancy that you know what you do not know. These are the limits of my art;
I can no further go, nor do I know aught of the things which great and
famous men know or have known in this or former ages. The office of a
midwife I, like my mother, have received from God; she delivered women, I
deliver men; but they must be young and noble and fair.

And now I have to go to the porch of the King Archon, where I am to meet
Meletus and his indictment. To-morrow morning, Theodorus, I shall hope to
see you again at this place.

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