Theodorus, a famous geometrician of Cyrene and a follower of Protagoras,
is represented to have met Socrates at Athens, and to have been asked by
him whether among his pupils there were any who promised to become
eminent. Theodorus particularizes one above all the rest, who, while he
is speaking, is seen approaching. His name is Theætetus. Socrates,
having heard him so highly spoken of by Theodorus, at once opens upon
the subject which he wishes to discuss, and asks What science is.
Theætetus, in answer, enumerates several particular sciences, but is
soon led to understand that the question is not, how many sciences there
are, but what science itself is; and by an instance in point shews that
he does so. Still he doubts his own ability to answer the question
proposed, but is at length induced to make the attempt by Socrates
pleasantly describing himself as inheriting his own mother’s skill in
midwifery, by which he is able to bring to the birth and deliver the
mental conceptions of those whose souls are pregnant with ideas[134].
-----
Footnote 134:
§ 1-22.
-----
Theætetus, then, first of all says that science is nothing else than
perception. This, Socrates observes, is the opinion of Protagoras,
differently expressed; for he said, that man is the measure of all
things, in other words that all things are such as they appear to each
person. In order to examine the truth of this doctrine Socrates begins
by stating it more fully. Protagoras asserts that nothing exists of
itself, nor can any thing be designated by any quality, for what we call
great will, in reference to something else, be also small, and what we
call heavy, light, and so on, so that nothing ever exists but is always
becoming. Consequently all things spring from motion, and the relation
that they bear to each other. Thus, with respect to colour, it does not
actually exist, it is neither in the object seen nor in the eye itself,
but results from the application of the eye to the object, and so is the
intermediate production of both. Again if you compare six with four they
appear to be half as many again, but if with twelve, only the half,
whence it appears that the same number is at one time great, at another
small, which would not be the case if numbers had a fixed and determined
magnitude. The principle then on which all things depend is this, That
the universe is nothing but motion, of which there are two species, the
one active, the other passive, by the union of which that which is
perceivable and perception itself consist. Thus when the eye and a
corresponding object, meeting together, produce whiteness and its
connate perception, the eye sees, and becomes not vision, but a seeing
eye, and the object itself becomes not whiteness but white: so that
nothing is essentially one, but is always being produced by something
else, and therefore the word “being” must be entirely done away with.
But here it may be objected that the perceptions produced in persons who
dream, or are diseased or mad, are utterly false, and so far are the
things that appear to them from existing, that none of them have any
real existence at all; how then can it be said that perception is
science, and that things which appear to every one are to that person
what they appear to be? The answer is, that the things which appear are
most certainly true to the percipient; just as if wine appears bitter to
a sick person, to him it is certainly bitter; and again with regard to
dreams, there is no certain way of distinguishing a state of being awake
from dreaming; and as the object perceived and the percipient exist or
are produced by relation to each other, neither exists or is produced of
itself, but the object perceived does exist in relation to the
percipient and to him is true, so that he has a scientific knowledge of
what he perceives[135].
-----
Footnote 135:
§ 23-46.
-----
Socrates then proposes to examine the correctness of Protagoras’s
theory. If what he says is true, a pig or any other creature that
possesses perception will be the measure of all things, as well as a
man, and man himself will be equal in wisdom to the gods. To which
Protagoras is supposed to answer, that the gods are not to be brought
into the question at all, for that it does not appear whether they exist
or not; and as to brute creatures, it would be strange if every man did
not excel them in wisdom, and besides no argument deduced from them can
be conclusive but rests only on probability, which cannot be allowed in
a discussion respecting science. Well then, when we hear barbarians
speak, whose language we have not learnt, are we to say that we both
hear and know what they say? to which the answer is, that we both hear
and know the sounds, but not the meaning of the words. Again it is
objected, if perception is science, a person may remember a thing and
not know it, for instance he may obtain a knowledge of a thing by seeing
it, and then shut his eyes, in that case he remembers it, but does not
see it, but inasmuch as sight is perception and perception knowledge, he
cannot know it, because he does not see it, and yet he remembers it;
which is absurd. But Protagoras will not admit this conclusion, but will
say that memory is very different from perception, and that the things
which we appear to remember are not the same as those that we formerly
perceived. Still, though all things are as they appear to each person,
it must be admitted that there is such a thing as wisdom and a wise man,
and he is wise who changes the aspect of objects to another, and causes
things that appear and are evil to any one, to appear and be good; just
as a physician by means of medicine changes the habit of the body from
bad to good[136].
-----
Footnote 136:
§ 47-65.
-----
Thus far Socrates had carried on the discussion with Theætetus, adducing
the answers which Protagoras himself would have given to the objections
brought against his theory, but expressing no opinion of his own. He now
persuades Theodorus to advocate the cause of Protagoras, and himself
undertakes to refute it. Protagoras, then, maintains that what appears
to each person exists to him to whom it appears; now all men think
themselves in some respects wiser than others, and others wiser than
themselves, so that all admit that there is wisdom and ignorance among
themselves. Now is not wisdom true opinion, and ignorance false opinion?
If so, some men form false opinions, and yet that could not be if man is
the measure of all things. Again, according to his doctrine, the same
thing will be both true and false; for instance, Protagoras’s own theory
will be true to himself, but false to all who do not agree with him, and
by how many more they are to whom it does not appear to be true than
those to whom it does so appear, by so much the more it is not than it
is: and so in admitting that the opinion of those who differ from him is
true he admits that his own opinion is false. Moreover, in political
matters Protagoras will admit that things honourable and base, just and
unjust, are such to each city as each city considers them; but he will
allow that one counsellor excels another, and that all laws are not
equally expedient, though the city that enacts them thinks them so[137].
-----
Footnote 137:
§ 66-75.
-----
The mention of political matters leads Socrates to interrupt the course
of the argument, and to contrast the life of a politician with that of a
philosopher, in which he shews how far more exalted are the views of the
latter than of the former. The digression, however, has this connexion
with the subject in hand, that it exposes the utter worthlessness of
political expediency, which depends on appearances only, and vindicates
the aspirations of philosophers, who devote themselves to the
contemplation of wisdom and true virtue[138].
-----
Footnote 138:
§ 76-87.
-----
To return, then, to the original subject. Those who maintain that
whatever appears to each person exists to him to whom it appears,
persist that what a city enacts as appearing just to itself is just to
that city as long as it continues in force; but in enacting laws the
real object is to make them as advantageous to itself as possible, but
what is advantageous regards also the future, for laws are enacted that
they may be advantageous for the future. But if man is the measure of
all things, he must also contain within himself the criterion of things
about to happen; yet it will be admitted, in a variety of instances that
are adduced, that a person who is skilled is better able to judge of the
future than one who is unskilled: and Protagoras himself can judge
beforehand better than any private person what arguments are likely to
be available in a court of justice, so that not every man, but the wise
man only, is the true measure of things[139].
-----
Footnote 139:
§ 87-91.
-----
This part of the argument being brought to a close, Socrates next
proposes to consider the essence that is said to consist in motion, a
doctrine which the followers of Heraclitus were then advocating very
strenuously. Now there are two species of motion, removal and change;
the former is when a thing passes from one place to another, the latter
a change of quality, as when a thing becomes black from white, or hard
from soft; and all things must undergo both kinds of motion, otherwise
the same thing would be both in motion and at rest at the same time, and
in that case it would not be more correct to say that all things are in
motion than that they are at rest. Since then every thing must be
continually undergoing a process of change at the same time that it is
in motion, there can be nothing fixed and certain, so that perception
cannot be science, for, as all things are in motion; perception itself,
which results from the relation between the object and the percipient,
must be in a constant state of motion and change[140].
-----
Footnote 140:
§ 91-100.
-----
Theætetus now resumes the argument, and though it would seem that
Protagoras’s doctrine had been already sufficiently refuted, yet
Socrates resolves to try it by one more test. Each sense has its
peculiar perception, and such things as are perceived by one faculty
cannot be perceived by another; for instance, what is perceived by
hearing cannot be perceived by sight, and what is perceived by sight
cannot be perceived by hearing; yet we can form a notion of them both
together, and observe what properties they have in common, and how they
differ: this, however, is not done by the senses, but by the soul
itself, for children as soon as they are born are able to perceive by
the bodily organs, but only arrive, with much labour and difficulty, at
the power of comparing things with each other, and so obtain a knowledge
of them, whence again it follows that perception and science are not the
same[141].
-----
Footnote 141:
§ 101-107.
-----
The first definition of science attempted by Theætetus being thus
overthrown, Socrates again asks him, What science is. To which he
answers that it appears to be true judgment. Socrates however thinks
proper first to enquire whether there is such a thing as false judgment.
People, he says, must either know or not know things about which they
form judgments. Now false judgments are formed, when a person thinks
that things which he does not know are certain other things that he does
not know, or when he thinks that things which he does know are other
things that he does know, or that things which he does not know are
things that he does know. But none of these things can happen, therefore
it is not possible to form false judgments. Again if existence is put
for knowledge a similar train of reasoning leads to the same conclusion.
A third method of forming false judgments may be when any one says that
any real object is another real object, changing one for the other in
his thoughts. But in that case he must think of both of them or one
only; if the former he would contradict himself; if the latter he cannot
judge that the one is the other, for he thinks of one only, so that
neither in this way can false judgment be formed. There still remains
another mode in which false judgments may be formed. Suppose that we
have in our souls a waxen tablet of various qualities in different
persons: on this tablet are impressed the images of our perceptions and
thoughts, and whatever is so impressed we remember and know so long as
the image remains. But by examining every possible mode by which
perception in the senses and impressions in the mind can be varied and
inter-changed, it will be found that false judgment takes place where
either the perception or the impression is imperfect and
indistinct[142].
-----
Footnote 142:
§ 108-125.
-----
Socrates, however, is not satisfied with this conclusion, that false
judgment proceeds from the conjunction of perception with thought, and
shews that the mind alone by itself may err, for instance a man may
think that seven and five make eleven, though he knows they make twelve;
so that there must be either no false judgment at all, or it is possible
for a person not to know what he knows. Theætetus is unable to choose
between these alternatives. Socrates therefore proposes to abandon their
present course of argument and at once to enquire what it is to know.
Some people say it is to have science, Socrates prefers saying it is to
possess science; for having differs from possessing in that what we
have, we use, but what we possess, we use or not as we please. Suppose
the soul then to be a kind of aviary containing all sorts of birds, and
let the birds stand for sciences; now all the sciences that are shut up
in this aviary a man may be said to possess, but when he has occasion to
use any particular science, he may by mistake take one instead of
another, thus when he thinks that eleven is twelve he takes the science
of eleven instead of that of twelve, and so judges falsely; but when he
takes that which he endeavours to take, he judges truly. Still another
even worse inconvenience appears to Socrates to follow from this; for it
is absurd to suppose that a person who has the science of any thing
should at the same time be ignorant of that thing; and if that can be,
nothing hinders but that ignorance when present should make us know
something. So that after all they have only come round again to the
point from whence they started and have still to enquire what science
is. Theætetus persists in answering that it is true judgment. But
Socrates shews that this cannot be the case; for that judges, who listen
to the arguments of lawyers, form true judgments without science, whence
it follows that true judgment and science are not the same[143].
-----
Footnote 143:
§ 126-138.
-----
Theætetus, pressed by this objection, attempts a third definition of
science, and says it is true judgment in conjunction with reason. But
then, observes Socrates, how are we to distinguish the things that can
be known from those that cannot? For instance, elements cannot be
defined, but things composed of them can be defined. Again, elements can
be perceived but not known, for he who cannot give an explanation of a
thing cannot know it, but things compounded of them, because they can be
defined, can also be known. Theætetus agrees to this; but Socrates is
not satisfied with the statement, that the elements are unknown, but the
nature of things compounded of them known. He illustrates his objection
by an examination of the component parts of a syllable, and shews that
if a whole is known its parts must also be known; if, then, letters are
the elements of a syllable, being also the parts of it, they must also
be known as well as the syllable[144].
-----
Footnote 144:
§ 139-149.
-----
But in order to ascertain the accuracy of Theætetus’s last definition of
science, it is necessary to determine the meaning of the word _logos_.
First of all, then, it may mean the expressing one’s thoughts by means
of words, but in that case there will be no difference between true
judgment and science. Secondly, it may mean the being able to describe a
thing by its elements; but this has been already answered in considering
the elements of syllables. Lastly, it may mean definition; but it is
absurd to say that science is true judgment joined to definition, for
definition can only be of that which a person already knows, so that
this would be to say that science is true judgment joined to
science[145].
-----
Footnote 145:
§ 149-157.
-----
At this point the argument is broken off, without having been brought to
any satisfactory conclusion. But Socrates requests that they may meet
again the following day and continue the discussion.