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INTRODUCTION AND ANALYSIS

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.'