INTRODUCTION TO THE THEÆTETUS.

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].

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 362object 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].

Socrates then proposes to examine the correctness of Protagoras’s 363theory. 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].

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 364to 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].

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].

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; 365but 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].

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].

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 366sight, 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].

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 367every 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].

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, 368whence it follows that true judgment and science are not the same^[143].

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].

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].

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.

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