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By Plato

Translated by Benjamin Jowett


Some dialogues of Plato are of so various a character that their relation to the other dialogues cannot be determined with any degree of certainty. The Theaetetus, like the Parmenides, has points of similarity both with his earlier and his later writings. The perfection of style, the humour, the dramatic interest, the complexity of structure, the fertility of illustration, the shifting of the points of view, are characteristic of his best period of authorship. The vain search, the negative conclusion, the figure of the midwives, the constant profession of ignorance on the part of Socrates, also bear the stamp of the early dialogues, in which the original Socrates is not yet Platonized. Had we no other indications, we should be disposed to range the Theaetetus with the Apology and the Phaedrus, and perhaps even with the Protagoras and the Laches.

But when we pass from the style to an examination of the subject, we trace a connection with the later rather than with the earlier dialogues. In the first place there is the connexion, indicated by Plato himself at the end of the dialogue, with the Sophist, to which in many respects the Theaetetus is so little akin. (1) The same persons reappear, including the younger Socrates, whose name is just mentioned in the Theaetetus; (2) the theory of rest, which Socrates has declined to consider, is resumed by the Eleatic Stranger; (3) there is a similar allusion in both dialogues to the meeting of Parmenides and Socrates (Theaet., Soph.); and (4) the inquiry into not-being in the Sophist supplements the question of false opinion which is raised in the Theaetetus. (Compare also Theaet. and Soph. for parallel turns of thought.) Secondly, the later date of the dialogue is confirmed by the absence of the doctrine of recollection and of any doctrine of ideas except that which derives them from generalization and from reflection of the mind upon itself. The general character of the Theaetetus is dialectical, and there are traces of the same Megarian influences which appear in the Parmenides, and which later writers, in their matter of fact way, have explained by the residence of Plato at Megara. Socrates disclaims the character of a professional eristic, and also, with a sort of ironical admiration, expresses his inability to attain the Megarian precision in the use of terms. Yet he too employs a similar sophistical skill in overturning every conceivable theory of knowledge.

The direct indications of a date amount to no more than this: the conversation is said to have taken place when Theaetetus was a youth, and shortly before the death of Socrates. At the time of his own death he is supposed to be a full-grown man. Allowing nine or ten years for the interval between youth and manhood, the dialogue could not have been written earlier than 390, when Plato was about thirty-nine years of age. No more definite date is indicated by the engagement in which Theaetetus is said to have fallen or to have been wounded, and which may have taken place any time during the Corinthian war, between the years 390-387. The later date which has been suggested, 369, when the Athenians and Lacedaemonians disputed the Isthmus with Epaminondas, would make the age of Theaetetus at his death forty-five or forty-six. This a little impairs the beauty of Socrates' remark, that 'he would be a great man if he lived.'

In this uncertainty about the place of the Theaetetus, it seemed better, as in the case of the Republic, Timaeus, Critias, to retain the order in which Plato himself has arranged this and the two companion dialogues. We cannot exclude the possibility which has been already noticed in reference to other works of Plato, that the Theaetetus may not have been all written continuously; or the probability that the Sophist and Politicus, which differ greatly in style, were only appended after a long interval of time. The allusion to Parmenides compared with the Sophist, would probably imply that the dialogue which is called by his name was already in existence; unless, indeed, we suppose the passage in which the allusion occurs to have been inserted afterwards. Again, the Theaetetus may be connected with the Gorgias, either dialogue from different points of view containing an analysis of the real and apparent (Schleiermacher); and both may be brought into relation with the Apology as illustrating the personal life of Socrates. The Philebus, too, may with equal reason be placed either after or before what, in the language of Thrasyllus, may be called the Second Platonic Trilogy. Both the Parmenides and the Sophist, and still more the Theaetetus, have points of affinity with the Cratylus, in which the principles of rest and motion are again contrasted, and the Sophistical or Protagorean theory of language is opposed to that which is attributed to the disciple of Heracleitus, not to speak of lesser resemblances in thought and language. The Parmenides, again, has been thought by some to hold an intermediate position between the Theaetetus and the Sophist; upon this view, the Sophist may be regarded as the answer to the problems about One and Being which have been raised in the Parmenides. Any of these arrangements may suggest new views to the student of Plato; none of them can lay claim to an exclusive probability in its favour.

The Theaetetus is one of the narrated dialogues of Plato, and is the only one which is supposed to have been written down. In a short introductory scene, Euclides and Terpsion are described as meeting before the door of Euclides' house in Megara. This may have been a spot familiar to Plato (for Megara was within a walk of Athens), but no importance can be attached to the accidental introduction of the founder of the Megarian philosophy. The real intention of the preface is to create an interest about the person of Theaetetus, who has just been carried up from the army at Corinth in a dying state. The expectation of his death recalls the promise of his youth, and especially the famous conversation which Socrates had with him when he was quite young, a few days before his own trial and death, as we are once more reminded at the end of the dialogue. Yet we may observe that Plato has himself forgotten this, when he represents Euclides as from time to time coming to Athens and correcting the copy from Socrates' own mouth. The narrative, having introduced Theaetetus, and having guaranteed the authenticity of the dialogue (compare Symposium, Phaedo, Parmenides), is then dropped. No further use is made of the device. As Plato himself remarks, who in this as in some other minute points is imitated by Cicero (De Amicitia), the interlocutory words are omitted.

Theaetetus, the hero of the battle of Corinth and of the dialogue, is a disciple of Theodorus, the great geometrician, whose science is thus indicated to be the propaedeutic to philosophy. An interest has been already excited about him by his approaching death, and now he is introduced to us anew by the praises of his master Theodorus. He is a youthful Socrates, and exhibits the same contrast of the fair soul and the ungainly face and frame, the Silenus mask and the god within, which are described in the Symposium. The picture which Theodorus gives of his courage and patience and intelligence and modesty is verified in the course of the dialogue. His courage is shown by his behaviour in the battle, and his other qualities shine forth as the argument proceeds. Socrates takes an evident delight in 'the wise Theaetetus,' who has more in him than 'many bearded men'; he is quite inspired by his answers. At first the youth is lost in wonder, and is almost too modest to speak, but, encouraged by Socrates, he rises to the occasion, and grows full of interest and enthusiasm about the great question. Like a youth, he has not finally made up his mind, and is very ready to follow the lead of Socrates, and to enter into each successive phase of the discussion which turns up. His great dialectical talent is shown in his power of drawing distinctions, and of foreseeing the consequences of his own answers. The enquiry about the nature of knowledge is not new to him; long ago he has felt the 'pang of philosophy,' and has experienced the youthful intoxication which is depicted in the Philebus. But he has hitherto been unable to make the transition from mathematics to metaphysics. He can form a general conception of square and oblong numbers, but he is unable to attain a similar expression of knowledge in the abstract. Yet at length he begins to recognize that there are universal conceptions of being, likeness, sameness, number, which the mind contemplates in herself, and with the help of Socrates is conducted from a theory of sense to a theory of ideas.

There is no reason to doubt that Theaetetus was a real person, whose name survived in the next generation. But neither can any importance be attached to the notices of him in Suidas and Proclus, which are probably based on the mention of him in Plato. According to a confused statement in Suidas, who mentions him twice over, first, as a pupil of Socrates, and then of Plato, he is said to have written the first work on the Five Solids. But no early authority cites the work, the invention of which may have been easily suggested by the division of roots, which Plato attributes to him, and the allusion to the backward state of solid geometry in the Republic. At any rate, there is no occasion to recall him to life again after the battle of Corinth, in order that we may allow time for the completion of such a work (Muller). We may also remark that such a supposition entirely destroys the pathetic interest of the introduction.

Theodorus, the geometrician, had once been the friend and disciple of Protagoras, but he is very reluctant to leave his retirement and defend his old master. He is too old to learn Socrates' game of question and answer, and prefers the digressions to the main argument, because he finds them easier to follow. The mathematician, as Socrates says in the Republic, is not capable of giving a reason in the same manner as the dialectician, and Theodorus could not therefore have been appropriately introduced as the chief respondent. But he may be fairly appealed to, when the honour of his master is at stake. He is the 'guardian of his orphans,' although this is a responsibility which he wishes to throw upon Callias, the friend and patron of all Sophists, declaring that he himself had early 'run away' from philosophy, and was absorbed in mathematics. His extreme dislike to the Heraclitean fanatics, which may be compared with the dislike of Theaetetus to the materialists, and his ready acceptance of the noble words of Socrates, are noticeable traits of character.

The Socrates of the Theaetetus is the same as the Socrates of the earlier dialogues. He is the invincible disputant, now advanced in years, of the Protagoras and Symposium; he is still pursuing his divine mission, his 'Herculean labours,' of which he has described the origin in the Apology; and he still hears the voice of his oracle, bidding him receive or not receive the truant souls. There he is supposed to have a mission to convict men of self-conceit; in the Theaetetus he has assigned to him by God the functions of a man-midwife, who delivers men of their thoughts, and under this character he is present throughout the dialogue. He is the true prophet who has an insight into the natures of men, and can divine their future; and he knows that sympathy is the secret power which unlocks their thoughts. The hit at Aristides, the son of Lysimachus, who was specially committed to his charge in the Laches, may be remarked by the way. The attempt to discover the definition of knowledge is in accordance with the character of Socrates as he is described in the Memorabilia, asking What is justice? what is temperance? and the like. But there is no reason to suppose that he would have analyzed the nature of perception, or traced the connexion of Protagoras and Heracleitus, or have raised the difficulty respecting false opinion. The humorous illustrations, as well as the serious thoughts, run through the dialogue. The snubnosedness of Theaetetus, a characteristic which he shares with Socrates, and the man-midwifery of Socrates, are not forgotten in the closing words. At the end of the dialogue, as in the Euthyphro, he is expecting to meet Meletus at the porch of the king Archon; but with the same indifference to the result which is everywhere displayed by him, he proposes that they shall reassemble on the following day at the same spot. The day comes, and in the Sophist the three friends again meet, but no further allusion is made to the trial, and the principal share in the argument is assigned, not to Socrates, but to an Eleatic stranger; the youthful Theaetetus also plays a different and less independent part. And there is no allusion in the Introduction to the second and third dialogues, which are afterwards appended. There seems, therefore, reason to think that there is a real change, both in the characters and in the design.

The dialogue is an enquiry into the nature of knowledge, which is interrupted by two digressions. The first is the digression about the midwives, which is also a leading thought or continuous image, like the wave in the Republic, appearing and reappearing at intervals. Again and again we are reminded that the successive conceptions of knowledge are extracted from Theaetetus, who in his turn truly declares that Socrates has got a great deal more out of him than ever was in him. Socrates is never weary of working out the image in humorous details,—discerning the symptoms of labour, carrying the child round the hearth, fearing that Theaetetus will bite him, comparing his conceptions to wind-eggs, asserting an hereditary right to the occupation. There is also a serious side to the image, which is an apt similitude of the Socratic theory of education (compare Republic, Sophist), and accords with the ironical spirit in which the wisest of men delights to speak of himself.

The other digression is the famous contrast of the lawyer and philosopher. This is a sort of landing-place or break in the middle of the dialogue. At the commencement of a great discussion, the reflection naturally arises, How happy are they who, like the philosopher, have time for such discussions (compare Republic)! There is no reason for the introduction of such a digression; nor is a reason always needed, any more than for the introduction of an episode in a poem, or of a topic in conversation. That which is given by Socrates is quite sufficient, viz. that the philosopher may talk and write as he pleases. But though not very closely connected, neither is the digression out of keeping with the rest of the dialogue. The philosopher naturally desires to pour forth the thoughts which are always present to him, and to discourse of the higher life. The idea of knowledge, although hard to be defined, is realised in the life of philosophy. And the contrast is the favourite antithesis between the world, in the various characters of sophist, lawyer, statesman, speaker, and the philosopher,—between opinion and knowledge,—between the conventional and the true.

The greater part of the dialogue is devoted to setting up and throwing down definitions of science and knowledge. Proceeding from the lower to the higher by three stages, in which perception, opinion, reasoning are successively examined, we first get rid of the confusion of the idea of knowledge and specific kinds of knowledge,—a confusion which has been already noticed in the Lysis, Laches, Meno, and other dialogues. In the infancy of logic, a form of thought has to be invented before the content can be filled up. We cannot define knowledge until the nature of definition has been ascertained. Having succeeded in making his meaning plain, Socrates proceeds to analyze (1) the first definition which Theaetetus proposes: 'Knowledge is sensible perception.' This is speedily identified with the Protagorean saying, 'Man is the measure of all things;' and of this again the foundation is discovered in the perpetual flux of Heracleitus. The relativeness of sensation is then developed at length, and for a moment the definition appears to be accepted. But soon the Protagorean thesis is pronounced to be suicidal; for the adversaries of Protagoras are as good a measure as he is, and they deny his doctrine. He is then supposed to reply that the perception may be true at any given instant. But the reply is in the end shown to be inconsistent with the Heraclitean foundation, on which the doctrine has been affirmed to rest. For if the Heraclitean flux is extended to every sort of change in every instant of time, how can any thought or word be detained even for an instant? Sensible perception, like everything else, is tumbling to pieces. Nor can Protagoras himself maintain that one man is as good as another in his knowledge of the future; and 'the expedient,' if not 'the just and true,' belongs to the sphere of the future.

And so we must ask again, What is knowledge? The comparison of sensations with one another implies a principle which is above sensation, and which resides in the mind itself. We are thus led to look for knowledge in a higher sphere, and accordingly Theaetetus, when again interrogated, replies (2) that 'knowledge is true opinion.' But how is false opinion possible? The Megarian or Eristic spirit within us revives the question, which has been already asked and indirectly answered in the Meno: 'How can a man be ignorant of that which he knows?' No answer is given to this not unanswerable question. The comparison of the mind to a block of wax, or to a decoy of birds, is found wanting.

But are we not inverting the natural order in looking for opinion before we have found knowledge? And knowledge is not true opinion; for the Athenian dicasts have true opinion but not knowledge. What then is knowledge? We answer (3), 'True opinion, with definition or explanation.' But all the different ways in which this statement may be understood are set aside, like the definitions of courage in the Laches, or of friendship in the Lysis, or of temperance in the Charmides. At length we arrive at the conclusion, in which nothing is concluded.

There are two special difficulties which beset the student of the Theaetetus: (1) he is uncertain how far he can trust Plato's account of the theory of Protagoras; and he is also uncertain (2) how far, and in what parts of the dialogue, Plato is expressing his own opinion. The dramatic character of the work renders the answer to both these questions difficult.

1. In reply to the first, we have only probabilities to offer. Three main points have to be decided: (a) Would Protagoras have identified his own thesis, 'Man is the measure of all things,' with the other, 'All knowledge is sensible perception'? (b) Would he have based the relativity of knowledge on the Heraclitean flux? (c) Would he have asserted the absoluteness of sensation at each instant? Of the work of Protagoras on 'Truth' we know nothing, with the exception of the two famous fragments, which are cited in this dialogue, 'Man is the measure of all things,' and, 'Whether there are gods or not, I cannot tell.' Nor have we any other trustworthy evidence of the tenets of Protagoras, or of the sense in which his words are used. For later writers, including Aristotle in his Metaphysics, have mixed up the Protagoras of Plato, as they have the Socrates of Plato, with the real person.

Returning then to the Theaetetus, as the only possible source from which an answer to these questions can be obtained, we may remark, that Plato had 'The Truth' of Protagoras before him, and frequently refers to the book. He seems to say expressly, that in this work the doctrine of the Heraclitean flux was not to be found; 'he told the real truth' (not in the book, which is so entitled, but) 'privately to his disciples,'—words which imply that the connexion between the doctrines of Protagoras and Heracleitus was not generally recognized in Greece, but was really discovered or invented by Plato. On the other hand, the doctrine that 'Man is the measure of all things,' is expressly identified by Socrates with the other statement, that 'What appears to each man is to him;' and a reference is made to the books in which the statement occurs;—this Theaetetus, who has 'often read the books,' is supposed to acknowledge (so Cratylus). And Protagoras, in the speech attributed to him, never says that he has been misunderstood: he rather seems to imply that the absoluteness of sensation at each instant was to be found in his words. He is only indignant at the 'reductio ad absurdum' devised by Socrates for his 'homo mensura,' which Theodorus also considers to be 'really too bad.'

The question may be raised, how far Plato in the Theaetetus could have misrepresented Protagoras without violating the laws of dramatic probability. Could he have pretended to cite from a well-known writing what was not to be found there? But such a shadowy enquiry is not worth pursuing further. We need only remember that in the criticism which follows of the thesis of Protagoras, we are criticizing the Protagoras of Plato, and not attempting to draw a precise line between his real sentiments and those which Plato has attributed to him.

2. The other difficulty is a more subtle, and also a more important one, because bearing on the general character of the Platonic dialogues. On a first reading of them, we are apt to imagine that the truth is only spoken by Socrates, who is never guilty of a fallacy himself, and is the great detector of the errors and fallacies of others. But this natural presumption is disturbed by the discovery that the Sophists are sometimes in the right and Socrates in the wrong. Like the hero of a novel, he is not to be supposed always to represent the sentiments of the author. There are few modern readers who do not side with Protagoras, rather than with Socrates, in the dialogue which is called by his name. The Cratylus presents a similar difficulty: in his etymologies, as in the number of the State, we cannot tell how far Socrates is serious; for the Socratic irony will not allow him to distinguish between his real and his assumed wisdom. No one is the superior of the invincible Socrates in argument (except in the first part of the Parmenides, where he is introduced as a youth); but he is by no means supposed to be in possession of the whole truth. Arguments are often put into his mouth (compare Introduction to the Gorgias) which must have seemed quite as untenable to Plato as to a modern writer. In this dialogue a great part of the answer of Protagoras is just and sound; remarks are made by him on verbal criticism, and on the importance of understanding an opponent's meaning, which are conceived in the true spirit of philosophy. And the distinction which he is supposed to draw between Eristic and Dialectic, is really a criticism of Plato on himself and his own criticism of Protagoras.

The difficulty seems to arise from not attending to the dramatic character of the writings of Plato. There are two, or more, sides to questions; and these are parted among the different speakers. Sometimes one view or aspect of a question is made to predominate over the rest, as in the Gorgias or Sophist; but in other dialogues truth is divided, as in the Laches and Protagoras, and the interest of the piece consists in the contrast of opinions. The confusion caused by the irony of Socrates, who, if he is true to his character, cannot say anything of his own knowledge, is increased by the circumstance that in the Theaetetus and some other dialogues he is occasionally playing both parts himself, and even charging his own arguments with unfairness. In the Theaetetus he is designedly held back from arriving at a conclusion. For we cannot suppose that Plato conceived a definition of knowledge to be impossible. But this is his manner of approaching and surrounding a question. The lights which he throws on his subject are indirect, but they are not the less real for that. He has no intention of proving a thesis by a cut-and-dried argument; nor does he imagine that a great philosophical problem can be tied up within the limits of a definition. If he has analyzed a proposition or notion, even with the severity of an impossible logic, if half-truths have been compared by him with other half-truths, if he has cleared up or advanced popular ideas, or illustrated a new method, his aim has been sufficiently accomplished.

The writings of Plato belong to an age in which the power of analysis had outrun the means of knowledge; and through a spurious use of dialectic, the distinctions which had been already 'won from the void and formless infinite,' seemed to be rapidly returning to their original chaos. The two great speculative philosophies, which a century earlier had so deeply impressed the mind of Hellas, were now degenerating into Eristic. The contemporaries of Plato and Socrates were vainly trying to find new combinations of them, or to transfer them from the object to the subject. The Megarians, in their first attempts to attain a severer logic, were making knowledge impossible (compare Theaet.). They were asserting 'the one good under many names,' and, like the Cynics, seem to have denied predication, while the Cynics themselves were depriving virtue of all which made virtue desirable in the eyes of Socrates and Plato. And besides these, we find mention in the later writings of Plato, especially in the Theaetetus, Sophist, and Laws, of certain impenetrable godless persons, who will not believe what they 'cannot hold in their hands'; and cannot be approached in argument, because they cannot argue (Theat; Soph.). No school of Greek philosophers exactly answers to these persons, in whom Plato may perhaps have blended some features of the Atomists with the vulgar materialistic tendencies of mankind in general (compare Introduction to the Sophist).

And not only was there a conflict of opinions, but the stage which the mind had reached presented other difficulties hardly intelligible to us, who live in a different cycle of human thought. All times of mental progress are times of confusion; we only see, or rather seem to see things clearly, when they have been long fixed and defined. In the age of Plato, the limits of the world of imagination and of pure abstraction, of the old world and the new, were not yet fixed. The Greeks, in the fourth century before Christ, had no words for 'subject' and 'object,' and no distinct conception of them; yet they were always hovering about the question involved in them. The analysis of sense, and the analysis of thought, were equally difficult to them; and hopelessly confused by the attempt to solve them, not through an appeal to facts, but by the help of general theories respecting the nature of the universe.

Plato, in his Theaetetus, gathers up the sceptical tendencies of his age, and compares them. But he does not seek to reconstruct out of them a theory of knowledge. The time at which such a theory could be framed had not yet arrived. For there was no measure of experience with which the ideas swarming in men's minds could be compared; the meaning of the word 'science' could scarcely be explained to them, except from the mathematical sciences, which alone offered the type of universality and certainty. Philosophy was becoming more and more vacant and abstract, and not only the Platonic Ideas and the Eleatic Being, but all abstractions seemed to be at variance with sense and at war with one another.

The want of the Greek mind in the fourth century before Christ was not another theory of rest or motion, or Being or atoms, but rather a philosophy which could free the mind from the power of abstractions and alternatives, and show how far rest and how far motion, how far the universal principle of Being and the multitudinous principle of atoms, entered into the composition of the world; which could distinguish between the true and false analogy, and allow the negative as well as the positive a place in human thought. To such a philosophy Plato, in the Theaetetus, offers many contributions. He has followed philosophy into the region of mythology, and pointed out the similarities of opposing phases of thought. He has also shown that extreme abstractions are self-destructive, and, indeed, hardly distinguishable from one another. But his intention is not to unravel the whole subject of knowledge, if this had been possible; and several times in the course of the dialogue he rejects explanations of knowledge which have germs of truth in them; as, for example, 'the resolution of the compound into the simple;' or 'right opinion with a mark of difference.'


Terpsion, who has come to Megara from the country, is described as having looked in vain for Euclides in the Agora; the latter explains that he has been down to the harbour, and on his way thither had met Theaetetus, who was being carried up from the army to Athens. He was scarcely alive, for he had been badly wounded at the battle of Corinth, and had taken the dysentery which prevailed in the camp. The mention of his condition suggests the reflection, 'What a loss he will be!' 'Yes, indeed,' replies Euclid; 'only just now I was hearing of his noble conduct in the battle.' 'That I should expect; but why did he not remain at Megara?' 'I wanted him to remain, but he would not; so I went with him as far as Erineum; and as I parted from him, I remembered that Socrates had seen him when he was a youth, and had a remarkable conversation with him, not long before his own death; and he then prophesied of him that he would be a great man if he lived.' 'How true that has been; how like all that Socrates said! And could you repeat the conversation?' 'Not from memory; but I took notes when I returned home, which I afterwards filled up at leisure, and got Socrates to correct them from time to time, when I came to Athens'...Terpsion had long intended to ask for a sight of this writing, of which he had already heard. They are both tired, and agree to rest and have the conversation read to them by a servant...'Here is the roll, Terpsion; I need only observe that I have omitted, for the sake of convenience, the interlocutory words, "said I," "said he"; and that Theaetetus, and Theodorus, the geometrician of Cyrene, are the persons with whom Socrates is conversing.'

Socrates begins by asking Theodorus whether, in his visit to Athens, he has found any Athenian youth likely to attain distinction in science. 'Yes, Socrates, there is one very remarkable youth, with whom I have become acquainted. He is no beauty, and therefore you need not imagine that I am in love with him; and, to say the truth, he is very like you, for he has a snub nose, and projecting eyes, although these features are not so marked in him as in you. He combines the most various qualities, quickness, patience, courage; and he is gentle as well as wise, always silently flowing on, like a river of oil. Look! he is the middle one of those who are entering the palaestra.'

Socrates, who does not know his name, recognizes him as the son of Euphronius, who was himself a good man and a rich. He is informed by Theodorus that the youth is named Theaetetus, but the property of his father has disappeared in the hands of trustees; this does not, however, prevent him from adding liberality to his other virtues. At the desire of Socrates he invites Theaetetus to sit by them.

'Yes,' says Socrates, 'that I may see in you, Theaetetus, the image of my ugly self, as Theodorus declares. Not that his remark is of any importance; for though he is a philosopher, he is not a painter, and therefore he is no judge of our faces; but, as he is a man of science, he may be a judge of our intellects. And if he were to praise the mental endowments of either of us, in that case the hearer of the eulogy ought to examine into what he says, and the subject should not refuse to be examined.' Theaetetus consents, and is caught in a trap (compare the similar trap which is laid for Theodorus). 'Then, Theaetetus, you will have to be examined, for Theodorus has been praising you in a style of which I never heard the like.' 'He was only jesting.' 'Nay, that is not his way; and I cannot allow you, on that pretence, to retract the assent which you have already given, or I shall make Theodorus repeat your praises, and swear to them.' Theaetetus, in reply, professes that he is willing to be examined, and Socrates begins by asking him what he learns of Theodorus. He is himself anxious to learn anything of anybody; and now he has a little question to which he wants Theaetetus or Theodorus (or whichever of the company would not be 'donkey' to the rest) to find an answer. Without further preface, but at the same time apologizing for his eagerness, he asks, 'What is knowledge?' Theodorus is too old to answer questions, and begs him to interrogate Theaetetus, who has the advantage of youth.

Theaetetus replies, that knowledge is what he learns of Theodorus, i.e. geometry and arithmetic; and that there are other kinds of knowledge—shoemaking, carpentering, and the like. But Socrates rejoins, that this answer contains too much and also too little. For although Theaetetus has enumerated several kinds of knowledge, he has not explained the common nature of them; as if he had been asked, 'What is clay?' and instead of saying 'Clay is moistened earth,' he had answered, 'There is one clay of image-makers, another of potters, another of oven-makers.' Theaetetus at once divines that Socrates means him to extend to all kinds of knowledge the same process of generalization which he has already learned to apply to arithmetic. For he has discovered a division of numbers into square numbers, 4, 9, 16, etc., which are composed of equal factors, and represent figures which have equal sides, and oblong numbers, 3, 5, 6, 7, etc., which are composed of unequal factors, and represent figures which have unequal sides. But he has never succeeded in attaining a similar conception of knowledge, though he has often tried; and, when this and similar questions were brought to him from Socrates, has been sorely distressed by them. Socrates explains to him that he is in labour. For men as well as women have pangs of labour; and both at times require the assistance of midwives. And he, Socrates, is a midwife, although this is a secret; he has inherited the art from his mother bold and bluff, and he ushers into light, not children, but the thoughts of men. Like the midwives, who are 'past bearing children,' he too can have no offspring—the God will not allow him to bring anything into the world of his own. He also reminds Theaetetus that the midwives are or ought to be the only matchmakers (this is the preparation for a biting jest); for those who reap the fruit are most likely to know on what soil the plants will grow. But respectable midwives avoid this department of practice—they do not want to be called procuresses. There are some other differences between the two sorts of pregnancy. For women do not bring into the world at one time real children and at another time idols which are with difficulty distinguished from them. 'At first,' says Socrates in his character of the man-midwife, 'my patients are barren and stolid, but after a while they "round apace," if the gods are propitious to them; and this is due not to me but to themselves; I and the god only assist in bringing their ideas to the birth. Many of them have left me too soon, and the result has been that they have produced abortions; or when I have delivered them of children they have lost them by an ill bringing up, and have ended by seeing themselves, as others see them, to be great fools. Aristides, the son of Lysimachus, is one of these, and there have been others. The truants often return to me and beg to be taken back; and then, if my familiar allows me, which is not always the case, I receive them, and they begin to grow again. There come to me also those who have nothing in them, and have no need of my art; and I am their matchmaker (see above), and marry them to Prodicus or some other inspired sage who is likely to suit them. I tell you this long story because I suspect that you are in labour. Come then to me, who am a midwife, and the son of a midwife, and I will deliver you. And do not bite me, as the women do, if I abstract your first-born; for I am acting out of good-will towards you; the God who is within me is the friend of man, though he will not allow me to dissemble the truth. Once more then, Theaetetus, I repeat my old question—"What is knowledge?" Take courage, and by the help of God you will discover an answer.' 'My answer is, that knowledge is perception.' 'That is the theory of Protagoras, who has another way of expressing the same thing when he says, "Man is the measure of all things." He was a very wise man, and we should try to understand him. In order to illustrate his meaning let me suppose that there is the same wind blowing in our faces, and one of us may be hot and the other cold. How is this? Protagoras will reply that the wind is hot to him who is cold, cold to him who is hot. And "is" means "appears," and when you say "appears to him," that means "he feels." Thus feeling, appearance, perception, coincide with being. I suspect, however, that this was only a "facon de parler," by which he imposed on the common herd like you and me; he told "the truth" (in allusion to the title of his book, which was called "The Truth") in secret to his disciples. For he was really a votary of that famous philosophy in which all things are said to be relative; nothing is great or small, or heavy or light, or one, but all is in motion and mixture and transition and flux and generation, not "being," as we ignorantly affirm, but "becoming." This has been the doctrine, not of Protagoras only, but of all philosophers, with the single exception of Parmenides; Empedocles, Heracleitus, and others, and all the poets, with Epicharmus, the king of Comedy, and Homer, the king of Tragedy, at their head, have said the same; the latter has these words—

"Ocean, whence the gods sprang, and mother Tethys."

And many arguments are used to show, that motion is the source of life, and rest of death: fire and warmth are produced by friction, and living creatures owe their origin to a similar cause; the bodily frame is preserved by exercise and destroyed by indolence; and if the sun ceased to move, "chaos would come again." Now apply this doctrine of "All is motion" to the senses, and first of all to the sense of sight. The colour of white, or any other colour, is neither in the eyes nor out of them, but ever in motion between the object and the eye, and varying in the case of every percipient. All is relative, and, as the followers of Protagoras remark, endless contradictions arise when we deny this; e.g. here are six dice; they are more than four and less than twelve; "more and also less," would you not say?' 'Yes.' 'But Protagoras will retort: "Can anything be more or less without addition or subtraction?"'

'I should say "No" if I were not afraid of contradicting my former answer.'

'And if you say "Yes," the tongue will escape conviction but not the mind, as Euripides would say?' 'True.' 'The thoroughbred Sophists, who know all that can be known, would have a sparring match over this, but you and I, who have no professional pride, want only to discover whether our ideas are clear and consistent. And we cannot be wrong in saying, first, that nothing can be greater or less while remaining equal; secondly, that there can be no becoming greater or less without addition or subtraction; thirdly, that what is and was not, cannot be without having become. But then how is this reconcilable with the case of the dice, and with similar examples?—that is the question.' 'I am often perplexed and amazed, Socrates, by these difficulties.' 'That is because you are a philosopher, for philosophy begins in wonder, and Iris is the child of Thaumas. Do you know the original principle on which the doctrine of Protagoras is based?' 'No.' 'Then I will tell you; but we must not let the uninitiated hear, and by the uninitiated I mean the obstinate people who believe in nothing which they cannot hold in their hands. The brethren whose mysteries I am about to unfold to you are far more ingenious. They maintain that all is motion; and that motion has two forms, action and passion, out of which endless phenomena are created, also in two forms—sense and the object of sense—which come to the birth together. There are two kinds of motions, a slow and a fast; the motions of the agent and the patient are slower, because they move and create in and about themselves, but the things which are born of them have a swifter motion, and pass rapidly from place to place. The eye and the appropriate object come together, and give birth to whiteness and the sensation of whiteness; the eye is filled with seeing, and becomes not sight but a seeing eye, and the object is filled with whiteness, and becomes not whiteness but white; and no other compound of either with another would have produced the same effect. All sensation is to be resolved into a similar combination of an agent and patient. Of either, taken separately, no idea can be formed; and the agent may become a patient, and the patient an agent. Hence there arises a general reflection that nothing is, but all things become; no name can detain or fix them. Are not these speculations charming, Theaetetus, and very good for a person in your interesting situation? I am offering you specimens of other men's wisdom, because I have no wisdom of my own, and I want to deliver you of something; and presently we will see whether you have brought forth wind or not. Tell me, then, what do you think of the notion that "All things are becoming"?'

'When I hear your arguments, I am marvellously ready to assent.'

'But I ought not to conceal from you that there is a serious objection which may be urged against this doctrine of Protagoras. For there are states, such as madness and dreaming, in which perception is false; and half our life is spent in dreaming; and who can say that at this instant we are not dreaming? Even the fancies of madmen are real at the time. But if knowledge is perception, how can we distinguish between the true and the false in such cases? Having stated the objection, I will now state the answer. Protagoras would deny the continuity of phenomena; he would say that what is different is entirely different, and whether active or passive has a different power. There are infinite agents and patients in the world, and these produce in every combination of them a different perception. Take myself as an instance:—Socrates may be ill or he may be well,—and remember that Socrates, with all his accidents, is spoken of. The wine which I drink when I am well is pleasant to me, but the same wine is unpleasant to me when I am ill. And there is nothing else from which I can receive the same impression, nor can another receive the same impression from the wine. Neither can I and the object of sense become separately what we become together. For the one in becoming is relative to the other, but they have no other relation; and the combination of them is absolute at each moment. (In modern language, the act of sensation is really indivisible, though capable of a mental analysis into subject and object.) My sensation alone is true, and true to me only. And therefore, as Protagoras says, "To myself I am the judge of what is and what is not." Thus the flux of Homer and Heracleitus, the great Protagorean saying that "Man is the measure of all things," the doctrine of Theaetetus that "Knowledge is perception," have all the same meaning. And this is thy new-born child, which by my art I have brought to light; and you must not be angry if instead of rearing your infant we expose him.'

'Theaetetus will not be angry,' says Theodorus; 'he is very good-natured. But I should like to know, Socrates, whether you mean to say that all this is untrue?'

'First reminding you that I am not the bag which contains the arguments, but that I extract them from Theaetetus, shall I tell you what amazes me in your friend Protagoras?'

'What may that be?'

'I like his doctrine that what appears is; but I wonder that he did not begin his great work on Truth with a declaration that a pig, or a dog-faced baboon, or any other monster which has sensation, is a measure of all things; then, while we were reverencing him as a god, he might have produced a magnificent effect by expounding to us that he was no wiser than a tadpole. For if sensations are always true, and one man's discernment is as good as another's, and every man is his own judge, and everything that he judges is right and true, then what need of Protagoras to be our instructor at a high figure; and why should we be less knowing than he is, or have to go to him, if every man is the measure of all things? My own art of midwifery, and all dialectic, is an enormous folly, if Protagoras' "Truth" be indeed truth, and the philosopher is not merely amusing himself by giving oracles out of his book.'

Theodorus thinks that Socrates is unjust to his master, Protagoras; but he is too old and stiff to try a fall with him, and therefore refers him to Theaetetus, who is already driven out of his former opinion by the arguments of Socrates.

Socrates then takes up the defence of Protagoras, who is supposed to reply in his own person—'Good people, you sit and declaim about the gods, of whose existence or non-existence I have nothing to say, or you discourse about man being reduced to the level of the brutes; but what proof have you of your statements? And yet surely you and Theodorus had better reflect whether probability is a safe guide. Theodorus would be a bad geometrician if he had nothing better to offer.'...Theaetetus is affected by the appeal to geometry, and Socrates is induced by him to put the question in a new form. He proceeds as follows:—'Should we say that we know what we see and hear,—e.g. the sound of words or the sight of letters in a foreign tongue?'

'We should say that the figures of the letters, and the pitch of the voice in uttering them, were known to us, but not the meaning of them.'

'Excellent; I want you to grow, and therefore I will leave that answer and ask another question: Is not seeing perceiving?' 'Very true.' 'And he who sees knows?' 'Yes.' 'And he who remembers, remembers that which he sees and knows?' 'Very true.' 'But if he closes his eyes, does he not remember?' 'He does.' 'Then he may remember and not see; and if seeing is knowing, he may remember and not know. Is not this a "reductio ad absurdum" of the hypothesis that knowledge is sensible perception? Yet perhaps we are crowing too soon; and if Protagoras, "the father of the myth," had been alive, the result might have been very different. But he is dead, and Theodorus, whom he left guardian of his "orphan," has not been very zealous in defending him.'

Theodorus objects that Callias is the true guardian, but he hopes that Socrates will come to the rescue. Socrates prefaces his defence by resuming the attack. He asks whether a man can know and not know at the same time? 'Impossible.' Quite possible, if you maintain that seeing is knowing. The confident adversary, suiting the action to the word, shuts one of your eyes; and now, says he, you see and do not see, but do you know and not know? And a fresh opponent darts from his ambush, and transfers to knowledge the terms which are commonly applied to sight. He asks whether you can know near and not at a distance; whether you can have a sharp and also a dull knowledge. While you are wondering at his incomparable wisdom, he gets you into his power, and you will not escape until you have come to an understanding with him about the money which is to be paid for your release.

But Protagoras has not yet made his defence; and already he may be heard contemptuously replying that he is not responsible for the admissions which were made by a boy, who could not foresee the coming move, and therefore had answered in a manner which enabled Socrates to raise a laugh against himself. 'But I cannot be fairly charged,' he will say, 'with an answer which I should not have given; for I never maintained that the memory of a feeling is the same as a feeling, or denied that a man might know and not know the same thing at the same time. Or, if you will have extreme precision, I say that man in different relations is many or rather infinite in number. And I challenge you, either to show that his perceptions are not individual, or that if they are, what appears to him is not what is. As to your pigs and baboons, you are yourself a pig, and you make my writings a sport of other swine. But I still affirm that man is the measure of all things, although I admit that one man may be a thousand times better than another, in proportion as he has better impressions. Neither do I deny the existence of wisdom or of the wise man. But I maintain that wisdom is a practical remedial power of turning evil into good, the bitterness of disease into the sweetness of health, and does not consist in any greater truth or superior knowledge. For the impressions of the sick are as true as the impressions of the healthy; and the sick are as wise as the healthy. Nor can any man be cured of a false opinion, for there is no such thing; but he may be cured of the evil habit which generates in him an evil opinion. This is effected in the body by the drugs of the physician, and in the soul by the words of the Sophist; and the new state or opinion is not truer, but only better than the old. And philosophers are not tadpoles, but physicians and husbandmen, who till the soil and infuse health into animals and plants, and make the good take the place of the evil, both in individuals and states. Wise and good rhetoricians make the good to appear just in states (for that is just which appears just to a state), and in return, they deserve to be well paid. And you, Socrates, whether you please or not, must continue to be a measure. This is my defence, and I must request you to meet me fairly. We are professing to reason, and not merely to dispute; and there is a great difference between reasoning and disputation. For the disputer is always seeking to trip up his opponent; and this is a mode of argument which disgusts men with philosophy as they grow older. But the reasoner is trying to understand him and to point out his errors to him, whether arising from his own or from his companion's fault; he does not argue from the customary use of names, which the vulgar pervert in all manner of ways. If you are gentle to an adversary he will follow and love you; and if defeated he will lay the blame on himself, and seek to escape from his own prejudices into philosophy. I would recommend you, Socrates, to adopt this humaner method, and to avoid captious and verbal criticisms.'

Such, Theodorus, is the very slight help which I am able to afford to your friend; had he been alive, he would have helped himself in far better style.

'You have made a most valorous defence.'

Yes; but did you observe that Protagoras bade me be serious, and complained of our getting up a laugh against him with the aid of a boy? He meant to intimate that you must take the place of Theaetetus, who may be wiser than many bearded men, but not wiser than you, Theodorus.

'The rule of the Spartan Palaestra is, Strip or depart; but you are like the giant Antaeus, and will not let me depart unless I try a fall with you.'

Yes, that is the nature of my complaint. And many a Hercules, many a Theseus mighty in deeds and words has broken my head; but I am always at this rough game. Please, then, to favour me.

'On the condition of not exceeding a single fall, I consent.'

Socrates now resumes the argument. As he is very desirous of doing justice to Protagoras, he insists on citing his own words,—'What appears to each man is to him.' And how, asks Socrates, are these words reconcileable with the fact that all mankind are agreed in thinking themselves wiser than others in some respects, and inferior to them in others? In the hour of danger they are ready to fall down and worship any one who is their superior in wisdom as if he were a god. And the world is full of men who are asking to be taught and willing to be ruled, and of other men who are willing to rule and teach them. All which implies that men do judge of one another's impressions, and think some wise and others foolish. How will Protagoras answer this argument? For he cannot say that no one deems another ignorant or mistaken. If you form a judgment, thousands and tens of thousands are ready to maintain the opposite. The multitude may not and do not agree in Protagoras' own thesis that 'Man is the measure of all things;' and then who is to decide? Upon his own showing must not his 'truth' depend on the number of suffrages, and be more or less true in proportion as he has more or fewer of them? And he must acknowledge further, that they speak truly who deny him to speak truly, which is a famous jest. And if he admits that they speak truly who deny him to speak truly, he must admit that he himself does not speak truly. But his opponents will refuse to admit this of themselves, and he must allow that they are right in their refusal. The conclusion is, that all mankind, including Protagoras himself, will deny that he speaks truly; and his truth will be true neither to himself nor to anybody else.

Theodorus is inclined to think that this is going too far. Socrates ironically replies, that he is not going beyond the truth. But if the old Protagoras could only pop his head out of the world below, he would doubtless give them both a sound castigation and be off to the shades in an instant. Seeing that he is not within call, we must examine the question for ourselves. It is clear that there are great differences in the understandings of men. Admitting, with Protagoras, that immediate sensations of hot, cold, and the like, are to each one such as they appear, yet this hypothesis cannot be extended to judgments or opinions. And even if we were to admit further,—and this is the view of some who are not thorough-going followers of Protagoras,—that right and wrong, holy and unholy, are to each state or individual such as they appear, still Protagoras will not venture to maintain that every man is equally the measure of expediency, or that the thing which seems is expedient to every one. But this begins a new question. 'Well, Socrates, we have plenty of leisure. Yes, we have, and, after the manner of philosophers, we are digressing; I have often observed how ridiculous this habit of theirs makes them when they appear in court. 'What do you mean?' I mean to say that a philosopher is a gentleman, but a lawyer is a servant. The one can have his talk out, and wander at will from one subject to another, as the fancy takes him; like ourselves, he may be long or short, as he pleases. But the lawyer is always in a hurry; there is the clepsydra limiting his time, and the brief limiting his topics, and his adversary is standing over him and exacting his rights. He is a servant disputing about a fellow-servant before his master, who holds the cause in his hands; the path never diverges, and often the race is for his life. Such experiences render him keen and shrewd; he learns the arts of flattery, and is perfect in the practice of crooked ways; dangers have come upon him too soon, when the tenderness of youth was unable to meet them with truth and honesty, and he has resorted to counter-acts of dishonesty and falsehood, and become warped and distorted; without any health or freedom or sincerity in him he has grown up to manhood, and is or esteems himself to be a master of cunning. Such are the lawyers; will you have the companion picture of philosophers? or will this be too much of a digression?

'Nay, Socrates, the argument is our servant, and not our master. Who is the judge or where is the spectator, having a right to control us?'

I will describe the leaders, then: for the inferior sort are not worth the trouble. The lords of philosophy have not learned the way to the dicastery or ecclesia; they neither see nor hear the laws and votes of the state, written or recited; societies, whether political or festive, clubs, and singing maidens do not enter even into their dreams. And the scandals of persons or their ancestors, male and female, they know no more than they can tell the number of pints in the ocean. Neither are they conscious of their own ignorance; for they do not practise singularity in order to gain reputation, but the truth is, that the outer form of them only is residing in the city; the inner man, as Pindar says, is going on a voyage of discovery, measuring as with line and rule the things which are under and in the earth, interrogating the whole of nature, only not condescending to notice what is near them.

'What do you mean, Socrates?'

I will illustrate my meaning by the jest of the witty maid-servant, who saw Thales tumbling into a well, and said of him, 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 applicable to all philosophers. The philosopher is unacquainted with the world; he hardly knows whether his neighbour is a man or an animal. For he is always searching into the essence of man, and enquiring what such a nature ought to do or suffer different from any other. Hence, on every occasion in private life and public, as I was saying, when he appears in a law-court or anywhere, he is the joke, not only of maid-servants, but of the general herd, falling into wells and every sort of disaster; he looks such an awkward, inexperienced creature, unable to say anything personal, when he is abused, in answer to his adversaries (for he knows no evil of any one); and when he hears the praises of others, he cannot help laughing from the bottom of his soul at their pretensions; and this also gives him a ridiculous appearance. A king or tyrant appears to him to be a kind of swine-herd or cow-herd, milking away at an animal who is much more troublesome and dangerous than cows or sheep; like the cow-herd, he has no time to be educated, and the pen in which he keeps his flock in the mountains is surrounded by a wall. When he hears of large landed properties of ten thousand acres or more, he thinks of the whole earth; or if he is told of the antiquity of a family, he remembers that every one has had myriads of progenitors, rich and poor, Greeks and barbarians, kings and slaves. And he who boasts of his descent from Amphitryon in the twenty-fifth generation, may, if he pleases, add as many more, and double that again, and our philosopher only laughs at his inability to do a larger sum. Such is the man at whom the vulgar scoff; he seems to them as if he could not mind his feet. 'That is very true, Socrates.' But when he tries to draw the quick-witted lawyer out of his pleas and rejoinders to the contemplation of absolute justice or injustice in their own nature, or from the popular praises of wealthy kings to the view of happiness and misery in themselves, or to the reasons why a man should seek after the one and avoid the other, then the situation is reversed; the little wretch turns giddy, and is ready to fall over the precipice; his utterance becomes thick, and he makes himself ridiculous, not to servant-maids, but to every man of liberal education. Such are the two pictures: the one of the philosopher and gentleman, who may be excused for not having learned how to make a bed, or cook up flatteries; the other, a serviceable knave, who hardly knows how to wear his cloak,—still less can he awaken harmonious thoughts or hymn virtue's praises.

'If the world, Socrates, were as ready to receive your words as I am, there would be greater peace and less evil among mankind.'

Evil, Theodorus, must ever remain in this world to be the antagonist of good, out of the way of the gods in heaven. Wherefore also we should fly away from ourselves to them; and to fly to them is to become like them; and to become like them is to become holy, just and true. But many live in the old wives' fable of appearances; they think that you should follow virtue in order that you may seem to be good. And yet the truth is, that God is righteous; and of men, he is most like him who is most righteous. To know this is wisdom; and in comparison of this the wisdom of the arts or the seeming wisdom of politicians is mean and common. The unrighteous man is apt to pride himself on his cunning; when others call him rogue, he says to himself: 'They only mean that I am one who deserves to live, and not a mere burden of the earth.' But he should reflect that his ignorance makes his condition worse than if he knew. For the penalty of injustice is not death or stripes, but the fatal necessity of becoming more and more unjust. Two patterns of life are set before him; the one blessed and divine, the other godless and wretched; and he is growing more and more like the one and unlike the other. He does not see that if he continues in his cunning, the place of innocence will not receive him after death. And yet if such a man has the courage to hear the argument out, he often becomes dissatisfied with himself, and has no more strength in him than a child.—But we have digressed enough.

'For my part, Socrates, I like the digressions better than the argument, because I understand them better.'

To return. When we left off, the Protagoreans and Heracliteans were maintaining that the ordinances of the State were just, while they lasted. But no one would maintain that the laws of the State were always good or expedient, although this may be the intention of them. For the expedient has to do with the future, about which we are liable to mistake. Now, would Protagoras maintain that man is the measure not only of the present and past, but of the future; and that there is no difference in the judgments of men about the future? Would an untrained man, for example, be as likely to know when he is going to have a fever, as the physician who attended him? And if they differ in opinion, which of them is likely to be right; or are they both right? Is not a vine-grower a better judge of a vintage which is not yet gathered, or a cook of a dinner which is in preparation, or Protagoras of the probable effect of a speech than an ordinary person? The last example speaks 'ad hominen.' For Protagoras would never have amassed a fortune if every man could judge of the future for himself. He is, therefore, compelled to admit that he is a measure; but I, who know nothing, am not equally convinced that I am. This is one way of refuting him; and he is refuted also by the authority which he attributes to the opinions of others, who deny his opinions. I am not equally sure that we can disprove the truth of immediate states of feeling. But this leads us to the doctrine of the universal flux, about which a battle-royal is always going on in the cities of Ionia. 'Yes; the Ephesians are downright mad about the flux; they cannot stop to argue with you, but are in perpetual motion, obedient to their text-books. Their restlessness is beyond expression, and if you ask any of them a question, they will not answer, but dart at you some unintelligible saying, and another and another, making no way either with themselves or with others; for nothing is fixed in them or their ideas,—they are at war with fixed principles.' I suppose, Theodorus, that you have never seen them in time of peace, when they discourse at leisure to their disciples? 'Disciples! they have none; they are a set of uneducated fanatics, and each of them says of the other that they have no knowledge. We must trust to ourselves, and not to them for the solution of the problem.' Well, the doctrine is old, being derived from the poets, who speak in a figure of Oceanus and Tethys; the truth was once concealed, but is now revealed by the superior wisdom of a later generation, and made intelligible to the cobbler, who, on hearing that all is in motion, and not some things only, as he ignorantly fancied, may be expected to fall down and worship his teachers. And the opposite doctrine must not be forgotten:—

'Alone being remains unmoved which is the name for all,'

as Parmenides affirms. Thus we are in the midst of the fray; both parties are dragging us to their side; and we are not certain which of them are in the right; and if neither, then we shall be in a ridiculous position, having to set up our own opinion against ancient and famous men.

Let us first approach the river-gods, or patrons of the flux.

When they speak of motion, must they not include two kinds of motion, change of place and change of nature?—And all things must be supposed to have both kinds of motion; for if not, the same things would be at rest and in motion, which is contrary to their theory. And did we not say, that all sensations arise thus: they move about between the agent and patient together with a perception, and the patient ceases to be a perceiving power and becomes a percipient, and the agent a quale instead of a quality; but neither has any absolute existence? But now we make the further discovery, that neither white or whiteness, nor any sense or sensation, can be predicated of anything, for they are in a perpetual flux. And therefore we must modify the doctrine of Theaetetus and Protagoras, by asserting further that knowledge is and is not sensation; and of everything we must say equally, that this is and is not, or becomes or becomes not. And still the word 'this' is not quite correct, for language fails in the attempt to express their meaning.

At the close of the discussion, Theodorus claims to be released from the argument, according to his agreement. But Theaetetus insists that they shall proceed to consider the doctrine of rest. This is declined by Socrates, who has too much reverence for the great Parmenides lightly to attack him. (We shall find that he returns to the doctrine of rest in the Sophist; but at present he does not wish to be diverted from his main purpose, which is, to deliver Theaetetus of his conception of knowledge.) He proceeds to interrogate him further. When he says that 'knowledge is in perception,' with what does he perceive? The first answer is, that he perceives sights with the eye, and sounds with the ear. This leads Socrates to make the reflection that nice distinctions of words are sometimes pedantic, but sometimes necessary; and he proposes in this case to substitute the word 'through' for 'with.' For the senses are not like the Trojan warriors in the horse, but have a common centre of perception, in which they all meet. This common principle is able to compare them with one another, and must therefore be distinct from them (compare Republic). And as there are facts of sense which are perceived through the organs of the body, there are also mathematical and other abstractions, such as sameness and difference, likeness and unlikeness, which the soul perceives by herself. Being is the most universal of these abstractions. The good and the beautiful are abstractions of another kind, which exist in relation and which above all others the mind perceives in herself, comparing within her past, present, and future. For example; we know a thing to be hard or soft by the touch, of which the perception is given at birth to men and animals. But the essence of hardness or softness, or the fact that this hardness is, and is the opposite of softness, is slowly learned by reflection and experience. Mere perception does not reach being, and therefore fails of truth; and therefore has no share in knowledge. But if so, knowledge is not perception. What then is knowledge? The mind, when occupied by herself with being, is said to have opinion—shall we say that 'Knowledge is true opinion'? But still an old difficulty recurs; we ask ourselves, 'How is false opinion possible?' This difficulty may be stated as follows:—

Either we know or do not know a thing (for the intermediate processes of learning and forgetting need not at present be considered); and in thinking or having an opinion, we must either know or not know that which we think, and we cannot know and be ignorant at the same time; we cannot confuse one thing which we do not know, with another thing which we do not know; nor can we think that which we do not know to be that which we know, or that which we know to be that which we do not know. And what other case is conceivable, upon the supposition that we either know or do not know all things? Let us try another answer in the sphere of being: 'When a man thinks, and thinks that which is not.' But would this hold in any parallel case? Can a man see and see nothing? or hear and hear nothing? or touch and touch nothing? Must he not see, hear, or touch some one existing thing? For if he thinks about nothing he does not think, and not thinking he cannot think falsely. And so the path of being is closed against us, as well as the path of knowledge. But may there not be 'heterodoxy,' or transference of opinion;—I mean, may not one thing be supposed to be another? Theaetetus is confident that this must be 'the true falsehood,' when a man puts good for evil or evil for good. Socrates will not discourage him by attacking the paradoxical expression 'true falsehood,' but passes on. The new notion involves a process of thinking about two things, either together or alternately. And thinking is the conversing of the mind with herself, which is carried on in question and answer, until she no longer doubts, but determines and forms an opinion. And false opinion consists in saying to yourself, that one thing is another. But did you ever say to yourself, that good is evil, or evil good? Even in sleep, did you ever imagine that odd was even? Or did any man in his senses ever fancy that an ox was a horse, or that two are one? So that we can never think one thing to be another; for you must not meet me with the verbal quibble that one—eteron—is other—eteron (both 'one' and 'other' in Greek are called 'other'—eteron). He who has both the two things in his mind, cannot misplace them; and he who has only one of them in his mind, cannot misplace them—on either supposition transplacement is inconceivable.

But perhaps there may still be a sense in which we can think that which we do not know to be that which we know: e.g. Theaetetus may know Socrates, but at a distance he may mistake another person for him. This process may be conceived by the help of an image. Let us suppose that every man has in his mind a block of wax of various qualities, the gift of Memory, the mother of the Muses; and on this he receives the seal or stamp of those sensations and perceptions which he wishes to remember. That which he succeeds in stamping is remembered and known by him as long as the impression lasts; but that, of which the impression is rubbed out or imperfectly made, is forgotten, and not known. No one can think one thing to be another, when he has the memorial or seal of both of these in his soul, and a sensible impression of neither; or when he knows one and does not know the other, and has no memorial or seal of the other; or when he knows neither; or when he perceives both, or one and not the other, or neither; or when he perceives and knows both, and identifies what he perceives with what he knows (this is still more impossible); or when he does not know one, and does not know and does not perceive the other; or does not perceive one, and does not know and does not perceive the other; or has no perception or knowledge of either—all these cases must be excluded. But he may err when he confuses what he knows or perceives, or what he perceives and does not know, with what he knows, or what he knows and perceives with what he knows and perceives.

Theaetetus is unable to follow these distinctions; which Socrates proceeds to illustrate by examples, first of all remarking, that knowledge may exist without perception, and perception without knowledge. I may know Theodorus and Theaetetus and not see them; I may see them, and not know them. 'That I understand.' But I could not mistake one for the other if I knew you both, and had no perception of either; or if I knew one only, and perceived neither; or if I knew and perceived neither, or in any other of the excluded cases. The only possibility of error is: 1st, when knowing you and Theodorus, and having the impression of both of you on the waxen block, I, seeing you both imperfectly and at a distance, put the foot in the wrong shoe—that is to say, put the seal or stamp on the wrong object: or 2ndly, when knowing both of you I only see one; or when, seeing and knowing you both, I fail to identify the impression and the object. But there could be no error when perception and knowledge correspond.

The waxen block in the heart of a man's soul, as I may say in the words of Homer, who played upon the words ker and keros, may be smooth and deep, and large enough, and then the signs are clearly marked and lasting, and do not get confused. But in the 'hairy heart,' as the all-wise poet sings, when the wax is muddy or hard or moist, there is a corresponding confusion and want of retentiveness; in the muddy and impure there is indistinctness, and still more in the hard, for there the impressions have no depth of wax, and in the moist they are too soon effaced. Yet greater is the indistinctness when they are all jolted together in a little soul, which is narrow and has no room. These are the sort of natures which have false opinion; from stupidity they see and hear and think amiss; and this is falsehood and ignorance. Error, then, is a confusion of thought and sense.

Theaetetus is delighted with this explanation. But Socrates has no sooner found the new solution than he sinks into a fit of despondency. For an objection occurs to him:—May there not be errors where there is no confusion of mind and sense? e.g. in numbers. No one can confuse the man whom he has in his thoughts with the horse which he has in his thoughts, but he may err in the addition of five and seven. And observe that these are purely mental conceptions. Thus we are involved once more in the dilemma of saying, either that there is no such thing as false opinion, or that a man knows what he does not know.

We are at our wit's end, and may therefore be excused for making a bold diversion. All this time we have been repeating the words 'know,' 'understand,' yet we do not know what knowledge is. 'Why, Socrates, how can you argue at all without using them?' Nay, but the true hero of dialectic would have forbidden me to use them until I had explained them. And I must explain them now. The verb 'to know' has two senses, to have and to possess knowledge, and I distinguish 'having' from 'possessing.' A man may possess a garment which he does not wear; or he may have wild birds in an aviary; these in one sense he possesses, and in another he has none of them. Let this aviary be an image of the mind, as the waxen block was; when we are young, the aviary is empty; after a time the birds are put in; for under this figure we may describe different forms of knowledge;—there are some of them in groups, and some single, which are flying about everywhere; and let us suppose a hunt after the science of odd and even, or some other science. The possession of the birds is clearly not the same as the having them in the hand. And the original chase of them is not the same as taking them in the hand when they are already caged.

This distinction between use and possession saves us from the absurdity of supposing that we do not know what we know, because we may know in one sense, i.e. possess, what we do not know in another, i.e. use. But have we not escaped one difficulty only to encounter a greater? For how can the exchange of two kinds of knowledge ever become false opinion? As well might we suppose that ignorance could make a man know, or that blindness could make him see. Theaetetus suggests that in the aviary there may be flying about mock birds, or forms of ignorance, and we put forth our hands and grasp ignorance, when we are intending to grasp knowledge. But how can he who knows the forms of knowledge and the forms of ignorance imagine one to be the other? Is there some other form of knowledge which distinguishes them? and another, and another? Thus we go round and round in a circle and make no progress.

All this confusion arises out of our attempt to explain false opinion without having explained knowledge. What then is knowledge? Theaetetus repeats that knowledge is true opinion. But this seems to be refuted by the instance of orators and judges. For surely the orator cannot convey a true knowledge of crimes at which the judges were not present; he can only persuade them, and the judge may form a true opinion and truly judge. But if true opinion were knowledge they could not have judged without knowledge.

Once more. Theaetetus offers a definition which he has heard: Knowledge is true opinion accompanied by definition or explanation. Socrates has had a similar dream, and has further heard that the first elements are names only, and that definition or explanation begins when they are combined; the letters are unknown, the syllables or combinations are known. But this new hypothesis when tested by the letters of the alphabet is found to break down. The first syllable of Socrates' name is SO. But what is SO? Two letters, S and O, a sibilant and a vowel, of which no further explanation can be given. And how can any one be ignorant of either of them, and yet know both of them? There is, however, another alternative:—We may suppose that the syllable has a separate form or idea distinct from the letters or parts. The all of the parts may not be the whole. Theaetetus is very much inclined to adopt this suggestion, but when interrogated by Socrates he is unable to draw any distinction between the whole and all the parts. And if the syllables have no parts, then they are those original elements of which there is no explanation. But how can the syllable be known if the letter remains unknown? In learning to read as children, we are first taught the letters and then the syllables. And in music, the notes, which are the letters, have a much more distinct meaning to us than the combination of them.

Once more, then, we must ask the meaning of the statement, that 'Knowledge is right opinion, accompanied by explanation or definition.' Explanation may mean, (1) the reflection or expression of a man's thoughts—but every man who is not deaf and dumb is able to express his thoughts—or (2) the enumeration of the elements of which anything is composed. A man may have a true opinion about a waggon, but then, and then only, has he knowledge of a waggon when he is able to enumerate the hundred planks of Hesiod. Or he may know the syllables of the name Theaetetus, but not the letters; yet not until he knows both can he be said to have knowledge as well as opinion. But on the other hand he may know the syllable 'The' in the name Theaetetus, yet he may be mistaken about the same syllable in the name Theodorus, and in learning to read we often make such mistakes. And even if he could write out all the letters and syllables of your name in order, still he would only have right opinion. Yet there may be a third meaning of the definition, besides the image or expression of the mind, and the enumeration of the elements, viz. (3) perception of difference.

For example, I may see a man who has eyes, nose, and mouth;—that will not distinguish him from any other man. Or he may have a snub-nose and prominent eyes;—that will not distinguish him from myself and you and others who are like me. But when I see a certain kind of snub-nosedness, then I recognize Theaetetus. And having this sign of difference, I have knowledge. But have I knowledge or opinion of this difference; if I have only opinion I have not knowledge; if I have knowledge we assume a disputed term; for knowledge will have to be defined as right opinion with knowledge of difference.

And so, Theaetetus, knowledge is neither perception nor true opinion, nor yet definition accompanying true opinion. And I have shown that the children of your brain are not worth rearing. Are you still in labour, or have you brought all you have to say about knowledge to the birth? If you have any more thoughts, you will be the better for having got rid of these; or if you have none, you will be the better for not fancying that you know what you do not know. Observe the limits of my art, which, like my mother's, is an art of midwifery; I do not pretend to compare with the good and wise of this and other ages.

And now I go to meet Meletus at the porch of the King Archon; but to-morrow I shall hope to see you again, Theodorus, at this place.


I. The saying of Theaetetus, that 'Knowledge is sensible perception,' may be assumed to be a current philosophical opinion of the age. 'The ancients,' as Aristotle (De Anim.) says, citing a verse of Empedocles, 'affirmed knowledge to be the same as perception.' We may now examine these words, first, with reference to their place in the history of philosophy, and secondly, in relation to modern speculations.

(a) In the age of Socrates the mind was passing from the object to the subject. The same impulse which a century before had led men to form conceptions of the world, now led them to frame general notions of the human faculties and feelings, such as memory, opinion, and the like. The simplest of these is sensation, or sensible perception, by which Plato seems to mean the generalized notion of feelings and impressions of sense, without determining whether they are conscious or not.

The theory that 'Knowledge is sensible perception' is the antithesis of that which derives knowledge from the mind (Theaet.), or which assumes the existence of ideas independent of the mind (Parm.). Yet from their extreme abstraction these theories do not represent the opposite poles of thought in the same way that the corresponding differences would in modern philosophy. The most ideal and the most sensational have a tendency to pass into one another; Heracleitus, like his great successor Hegel, has both aspects. The Eleatic isolation of Being and the Megarian or Cynic isolation of individuals are placed in the same class by Plato (Soph.); and the same principle which is the symbol of motion to one mind is the symbol of rest to another. The Atomists, who are sometimes regarded as the Materialists of Plato, denied the reality of sensation. And in the ancient as well as the modern world there were reactions from theory to experience, from ideas to sense. This is a point of view from which the philosophy of sensation presented great attraction to the ancient thinker. Amid the conflict of ideas and the variety of opinions, the impression of sense remained certain and uniform. Hardness, softness, cold, heat, etc. are not absolutely the same to different persons, but the art of measuring could at any rate reduce them all to definite natures (Republic). Thus the doctrine that knowledge is perception supplies or seems to supply a firm standing ground. Like the other notions of the earlier Greek philosophy, it was held in a very simple way, without much basis of reasoning, and without suggesting the questions which naturally arise in our own minds on the same subject.

(b) The fixedness of impressions of sense furnishes a link of connexion between ancient and modern philosophy. The modern thinker often repeats the parallel axiom, 'All knowledge is experience.' He means to say that the outward and not the inward is both the original source and the final criterion of truth, because the outward can be observed and analyzed; the inward is only known by external results, and is dimly perceived by each man for himself. In what does this differ from the saying of Theaetetus? Chiefly in this—that the modern term 'experience,' while implying a point of departure in sense and a return to sense, also includes all the processes of reasoning and imagination which have intervened. The necessary connexion between them by no means affords a measure of the relative degree of importance which is to be ascribed to either element. For the inductive portion of any science may be small, as in mathematics or ethics, compared with that which the mind has attained by reasoning and reflection on a very few facts.

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