The Protagoras, like several of the Dialogues of Plato, is put into the mouth of Socrates, who describes a conversation which had taken place between himself and the great Sophist at the house of Callias—'the man who had spent more upon the Sophists than all the rest of the world'—and in which the learned Hippias and the grammarian Prodicus had also shared, as well as Alcibiades and Critias, both of whom said a few words—in the presence of a distinguished company consisting of disciples of Protagoras and of leading Athenians belonging to the Socratic circle. The dialogue commences with a request on the part of Hippocrates that Socrates would introduce him to the celebrated teacher. He has come before the dawn had risen—so fervid is his zeal. Socrates moderates his excitement and advises him to find out 'what Protagoras will make of him,' before he becomes his pupil.

They go together to the house of Callias; and Socrates, after explaining the purpose of their visit to Protagoras, asks the question, 'What he will make of Hippocrates.' Protagoras answers, 'That he will make him a better and a wiser man.' 'But in what will he be better?'—Socrates desires to have a more precise answer. Protagoras replies, 'That he will teach him prudence in affairs private and public; in short, the science or knowledge of human life.'

This, as Socrates admits, is a noble profession; but he is or rather would have been doubtful, whether such knowledge can be taught, if Protagoras had not assured him of the fact, for two reasons: (1) Because the Athenian people, who recognize in their assemblies the distinction between the skilled and the unskilled in the arts, do not distinguish between the trained politician and the untrained; (2) Because the wisest and best Athenian citizens do not teach their sons political virtue. Will Protagoras answer these objections?

Protagoras explains his views in the form of an apologue, in which, after Prometheus had given men the arts, Zeus is represented as sending Hermes to them, bearing with him Justice and Reverence. These are not, like the arts, to be imparted to a few only, but all men are to be partakers of them. Therefore the Athenian people are right in distinguishing between the skilled and unskilled in the arts, and not between skilled and unskilled politicians. (1) For all men have the political virtues to a certain degree, and are obliged to say that they have them, whether they have them or not. A man would be thought a madman who professed an art which he did not know; but he would be equally thought a madman if he did not profess a virtue which he had not. (2) And that the political virtues can be taught and acquired, in the opinion of the Athenians, is proved by the fact that they punish evil-doers, with a view to prevention, of course—mere retribution is for beasts, and not for men. (3) Again, would parents who teach her sons lesser matters leave them ignorant of the common duty of citizens? To the doubt of Socrates the best answer is the fact, that the education of youth in virtue begins almost as soon as they can speak, and is continued by the state when they pass out of the parental control. (4) Nor need we wonder that wise and good fathers sometimes have foolish and worthless sons. Virtue, as we were saying, is not the private possession of any man, but is shared by all, only however to the extent of which each individual is by nature capable. And, as a matter of fact, even the worst of civilized mankind will appear virtuous and just, if we compare them with savages. (5) The error of Socrates lies in supposing that there are no teachers of virtue, whereas all men are teachers in a degree. Some, like Protagoras, are better than others, and with this result we ought to be satisfied.

Socrates is highly delighted with the explanation of Protagoras. But he has still a doubt lingering in his mind. Protagoras has spoken of the virtues: are they many, or one? are they parts of a whole, or different names of the same thing? Protagoras replies that they are parts, like the parts of a face, which have their several functions, and no one part is like any other part. This admission, which has been somewhat hastily made, is now taken up and cross-examined by Socrates:—

'Is justice just, and is holiness holy? And are justice and holiness opposed to one another?'—'Then justice is unholy.' Protagoras would rather say that justice is different from holiness, and yet in a certain point of view nearly the same. He does not, however, escape in this way from the cunning of Socrates, who inveigles him into an admission that everything has but one opposite. Folly, for example, is opposed to wisdom; and folly is also opposed to temperance; and therefore temperance and wisdom are the same. And holiness has been already admitted to be nearly the same as justice. Temperance, therefore, has now to be compared with justice.

Protagoras, whose temper begins to get a little ruffled at the process to which he has been subjected, is aware that he will soon be compelled by the dialectics of Socrates to admit that the temperate is the just. He therefore defends himself with his favourite weapon; that is to say, he makes a long speech not much to the point, which elicits the applause of the audience.

Here occurs a sort of interlude, which commences with a declaration on the part of Socrates that he cannot follow a long speech, and therefore he must beg Protagoras to speak shorter. As Protagoras declines to accommodate him, he rises to depart, but is detained by Callias, who thinks him unreasonable in not allowing Protagoras the liberty which he takes himself of speaking as he likes. But Alcibiades answers that the two cases are not parallel. For Socrates admits his inability to speak long; will Protagoras in like manner acknowledge his inability to speak short?

Counsels of moderation are urged first in a few words by Critias, and then by Prodicus in balanced and sententious language: and Hippias proposes an umpire. But who is to be the umpire? rejoins Socrates; he would rather suggest as a compromise that Protagoras shall ask and he will answer, and that when Protagoras is tired of asking he himself will ask and Protagoras shall answer. To this the latter yields a reluctant assent.

Protagoras selects as his thesis a poem of Simonides of Ceos, in which he professes to find a contradiction. First the poet says,

and then reproaches Pittacus for having said, 'Hard is it to be good.' How is this to be reconciled? Socrates, who is familiar with the poem, is embarrassed at first, and invokes the aid of Prodicus, the countryman of Simonides, but apparently only with the intention of flattering him into absurdities. First a distinction is drawn between (Greek) to be, and (Greek) to become: to become good is difficult; to be good is easy. Then the word difficult or hard is explained to mean 'evil' in the Cean dialect. To all this Prodicus assents; but when Protagoras reclaims, Socrates slily withdraws Prodicus from the fray, under the pretence that his assent was only intended to test the wits of his adversary. He then proceeds to give another and more elaborate explanation of the whole passage. The explanation is as follows:—

The Lacedaemonians are great philosophers (although this is a fact which is not generally known); and the soul of their philosophy is brevity, which was also the style of primitive antiquity and of the seven sages. Now Pittacus had a saying, 'Hard is it to be good:' and Simonides, who was jealous of the fame of this saying, wrote a poem which was designed to controvert it. No, says he, Pittacus; not 'hard to be good,' but 'hard to become good.' Socrates proceeds to argue in a highly impressive manner that the whole composition is intended as an attack upon Pittacus. This, though manifestly absurd, is accepted by the company, and meets with the special approval of Hippias, who has however a favourite interpretation of his own, which he is requested by Alcibiades to defer.

The argument is now resumed, not without some disdainful remarks of Socrates on the practice of introducing the poets, who ought not to be allowed, any more than flute-girls, to come into good society. Men's own thoughts should supply them with the materials for discussion. A few soothing flatteries are addressed to Protagoras by Callias and Socrates, and then the old question is repeated, 'Whether the virtues are one or many?' To which Protagoras is now disposed to reply, that four out of the five virtues are in some degree similar; but he still contends that the fifth, courage, is unlike the rest. Socrates proceeds to undermine the last stronghold of the adversary, first obtaining from him the admission that all virtue is in the highest degree good:—

The courageous are the confident; and the confident are those who know their business or profession: those who have no such knowledge and are still confident are madmen. This is admitted. Then, says Socrates, courage is knowledge—an inference which Protagoras evades by drawing a futile distinction between the courageous and the confident in a fluent speech.

Socrates renews the attack from another side: he would like to know whether pleasure is not the only good, and pain the only evil? Protagoras seems to doubt the morality or propriety of assenting to this; he would rather say that 'some pleasures are good, some pains are evil,' which is also the opinion of the generality of mankind. What does he think of knowledge? Does he agree with the common opinion that knowledge is overcome by passion? or does he hold that knowledge is power? Protagoras agrees that knowledge is certainly a governing power.

This, however, is not the doctrine of men in general, who maintain that many who know what is best, act contrary to their knowledge under the influence of pleasure. But this opposition of good and evil is really the opposition of a greater or lesser amount of pleasure. Pleasures are evils because they end in pain, and pains are goods because they end in pleasures. Thus pleasure is seen to be the only good; and the only evil is the preference of the lesser pleasure to the greater. But then comes in the illusion of distance. Some art of mensuration is required in order to show us pleasures and pains in their true proportion. This art of mensuration is a kind of knowledge, and knowledge is thus proved once more to be the governing principle of human life, and ignorance the origin of all evil: for no one prefers the less pleasure to the greater, or the greater pain to the less, except from ignorance. The argument is drawn out in an imaginary 'dialogue within a dialogue,' conducted by Socrates and Protagoras on the one part, and the rest of the world on the other. Hippias and Prodicus, as well as Protagoras, admit the soundness of the conclusion.

Socrates then applies this new conclusion to the case of courage—the only virtue which still holds out against the assaults of the Socratic dialectic. No one chooses the evil or refuses the good except through ignorance. This explains why cowards refuse to go to war:—because they form a wrong estimate of good, and honour, and pleasure. And why are the courageous willing to go to war?—because they form a right estimate of pleasures and pains, of things terrible and not terrible. Courage then is knowledge, and cowardice is ignorance. And the five virtues, which were originally maintained to have five different natures, after having been easily reduced to two only, at last coalesce in one. The assent of Protagoras to this last position is extracted with great difficulty.

Socrates concludes by professing his disinterested love of the truth, and remarks on the singular manner in which he and his adversary had changed sides. Protagoras began by asserting, and Socrates by denying, the teachableness of virtue, and now the latter ends by affirming that virtue is knowledge, which is the most teachable of all things, while Protagoras has been striving to show that virtue is not knowledge, and this is almost equivalent to saying that virtue cannot be taught. He is not satisfied with the result, and would like to renew the enquiry with the help of Protagoras in a different order, asking (1) What virtue is, and (2) Whether virtue can be taught. Protagoras declines this offer, but commends Socrates' earnestness and his style of discussion.

The Protagoras is often supposed to be full of difficulties. These are partly imaginary and partly real. The imaginary ones are (1) Chronological,—which were pointed out in ancient times by Athenaeus, and are noticed by Schleiermacher and others, and relate to the impossibility of all the persons in the Dialogue meeting at any one time, whether in the year 425 B.C., or in any other. But Plato, like all writers of fiction, aims only at the probable, and shows in many Dialogues (e.g. the Symposium and Republic, and already in the Laches) an extreme disregard of the historical accuracy which is sometimes demanded of him. (2) The exact place of the Protagoras among the Dialogues, and the date of composition, have also been much disputed. But there are no criteria which afford any real grounds for determining the date of composition; and the affinities of the Dialogues, when they are not indicated by Plato himself, must always to a great extent remain uncertain. (3) There is another class of difficulties, which may be ascribed to preconceived notions of commentators, who imagine that Protagoras the Sophist ought always to be in the wrong, and his adversary Socrates in the right; or that in this or that passage—e.g. in the explanation of good as pleasure—Plato is inconsistent with himself; or that the Dialogue fails in unity, and has not a proper beginning, middle, and ending. They seem to forget that Plato is a dramatic writer who throws his thoughts into both sides of the argument, and certainly does not aim at any unity which is inconsistent with freedom, and with a natural or even wild manner of treating his subject; also that his mode of revealing the truth is by lights and shadows, and far-off and opposing points of view, and not by dogmatic statements or definite results.

The real difficulties arise out of the extreme subtlety of the work, which, as Socrates says of the poem of Simonides, is a most perfect piece of art. There are dramatic contrasts and interests, threads of philosophy broken and resumed, satirical reflections on mankind, veils thrown over truths which are lightly suggested, and all woven together in a single design, and moving towards one end.

In the introductory scene Plato raises the expectation that a 'great personage' is about to appear on the stage; perhaps with a further view of showing that he is destined to be overthrown by a greater still, who makes no pretensions. Before introducing Hippocrates to him, Socrates thinks proper to warn the youth against the dangers of 'influence,' of which the invidious nature is recognized by Protagoras himself. Hippocrates readily adopts the suggestion of Socrates that he shall learn of Protagoras only the accomplishments which befit an Athenian gentleman, and let alone his 'sophistry.' There is nothing however in the introduction which leads to the inference that Plato intended to blacken the character of the Sophists; he only makes a little merry at their expense.

The 'great personage' is somewhat ostentatious, but frank and honest. He is introduced on a stage which is worthy of him—at the house of the rich Callias, in which are congregated the noblest and wisest of the Athenians. He considers openness to be the best policy, and particularly mentions his own liberal mode of dealing with his pupils, as if in answer to the favourite accusation of the Sophists that they received pay. He is remarkable for the good temper which he exhibits throughout the discussion under the trying and often sophistical cross-examination of Socrates. Although once or twice ruffled, and reluctant to continue the discussion, he parts company on perfectly good terms, and appears to be, as he says of himself, the 'least jealous of mankind.'

Nor is there anything in the sentiments of Protagoras which impairs this pleasing impression of the grave and weighty old man. His real defect is that he is inferior to Socrates in dialectics. The opposition between him and Socrates is not the opposition of good and bad, true and false, but of the old art of rhetoric and the new science of interrogation and argument; also of the irony of Socrates and the self-assertion of the Sophists. There is quite as much truth on the side of Protagoras as of Socrates; but the truth of Protagoras is based on common sense and common maxims of morality, while that of Socrates is paradoxical or transcendental, and though full of meaning and insight, hardly intelligible to the rest of mankind. Here as elsewhere is the usual contrast between the Sophists representing average public opinion and Socrates seeking for increased clearness and unity of ideas. But to a great extent Protagoras has the best of the argument and represents the better mind of man.

For example: (1) one of the noblest statements to be found in antiquity about the preventive nature of punishment is put into his mouth; (2) he is clearly right also in maintaining that virtue can be taught (which Socrates himself, at the end of the Dialogue, is disposed to concede); and also (3) in his explanation of the phenomenon that good fathers have bad sons; (4) he is right also in observing that the virtues are not like the arts, gifts or attainments of special individuals, but the common property of all: this, which in all ages has been the strength and weakness of ethics and politics, is deeply seated in human nature; (5) there is a sort of half-truth in the notion that all civilized men are teachers of virtue; and more than a half-truth (6) in ascribing to man, who in his outward conditions is more helpless than the other animals, the power of self-improvement; (7) the religious allegory should be noticed, in which the arts are said to be given by Prometheus (who stole them), whereas justice and reverence and the political virtues could only be imparted by Zeus; (8) in the latter part of the Dialogue, when Socrates is arguing that 'pleasure is the only good,' Protagoras deems it more in accordance with his character to maintain that 'some pleasures only are good;' and admits that 'he, above all other men, is bound to say "that wisdom and knowledge are the highest of human things."'

There is no reason to suppose that in all this Plato is depicting an imaginary Protagoras; he seems to be showing us the teaching of the Sophists under the milder aspect under which he once regarded them. Nor is there any reason to doubt that Socrates is equally an historical character, paradoxical, ironical, tiresome, but seeking for the unity of virtue and knowledge as for a precious treasure; willing to rest this even on a calculation of pleasure, and irresistible here, as everywhere in Plato, in his intellectual superiority.

The aim of Socrates, and of the Dialogue, is to show the unity of virtue. In the determination of this question the identity of virtue and knowledge is found to be involved. But if virtue and knowledge are one, then virtue can be taught; the end of the Dialogue returns to the beginning. Had Protagoras been allowed by Plato to make the Aristotelian distinction, and say that virtue is not knowledge, but is accompanied with knowledge; or to point out with Aristotle that the same quality may have more than one opposite; or with Plato himself in the Phaedo to deny that good is a mere exchange of a greater pleasure for a less—the unity of virtue and the identity of virtue and knowledge would have required to be proved by other arguments.

The victory of Socrates over Protagoras is in every way complete when their minds are fairly brought together. Protagoras falls before him after two or three blows. Socrates partially gains his object in the first part of the Dialogue, and completely in the second. Nor does he appear at any disadvantage when subjected to 'the question' by Protagoras. He succeeds in making his two 'friends,' Prodicus and Hippias, ludicrous by the way; he also makes a long speech in defence of the poem of Simonides, after the manner of the Sophists, showing, as Alcibiades says, that he is only pretending to have a bad memory, and that he and not Protagoras is really a master in the two styles of speaking; and that he can undertake, not one side of the argument only, but both, when Protagoras begins to break down. Against the authority of the poets with whom Protagoras has ingeniously identified himself at the commencement of the Dialogue, Socrates sets up the proverbial philosophers and those masters of brevity the Lacedaemonians. The poets, the Laconizers, and Protagoras are satirized at the same time.

Not having the whole of this poem before us, it is impossible for us to answer certainly the question of Protagoras, how the two passages of Simonides are to be reconciled. We can only follow the indications given by Plato himself. But it seems likely that the reconcilement offered by Socrates is a caricature of the methods of interpretation which were practised by the Sophists—for the following reasons: (1) The transparent irony of the previous interpretations given by Socrates. (2) The ludicrous opening of the speech in which the Lacedaemonians are described as the true philosophers, and Laconic brevity as the true form of philosophy, evidently with an allusion to Protagoras' long speeches. (3) The manifest futility and absurdity of the explanation of (Greek), which is hardly consistent with the rational interpretation of the rest of the poem. The opposition of (Greek) and (Greek) seems also intended to express the rival doctrines of Socrates and Protagoras, and is a facetious commentary on their differences. (4) The general treatment in Plato both of the Poets and the Sophists, who are their interpreters, and whom he delights to identify with them. (5) The depreciating spirit in which Socrates speaks of the introduction of the poets as a substitute for original conversation, which is intended to contrast with Protagoras' exaltation of the study of them—this again is hardly consistent with the serious defence of Simonides. (6) the marked approval of Hippias, who is supposed at once to catch the familiar sound, just as in the previous conversation Prodicus is represented as ready to accept any distinctions of language however absurd. At the same time Hippias is desirous of substituting a new interpretation of his own; as if the words might really be made to mean anything, and were only to be regarded as affording a field for the ingenuity of the interpreter.

This curious passage is, therefore, to be regarded as Plato's satire on the tedious and hypercritical arts of interpretation which prevailed in his own day, and may be compared with his condemnation of the same arts when applied to mythology in the Phaedrus, and with his other parodies, e.g. with the two first speeches in the Phaedrus and with the Menexenus. Several lesser touches of satire may be observed, such as the claim of philosophy advanced for the Lacedaemonians, which is a parody of the claims advanced for the Poets by Protagoras; the mistake of the Laconizing set in supposing that the Lacedaemonians are a great nation because they bruise their ears; the far-fetched notion, which is 'really too bad,' that Simonides uses the Lesbian (?) word, (Greek), because he is addressing a Lesbian. The whole may also be considered as a satire on those who spin pompous theories out of nothing. As in the arguments of the Euthydemus and of the Cratylus, the veil of irony is never withdrawn; and we are left in doubt at last how far in this interpretation of Simonides Socrates is 'fooling,' how far he is in earnest.

All the interests and contrasts of character in a great dramatic work like the Protagoras are not easily exhausted. The impressiveness of the scene should not be lost upon us, or the gradual substitution of Socrates in the second part for Protagoras in the first. The characters to whom we are introduced at the beginning of the Dialogue all play a part more or less conspicuous towards the end. There is Alcibiades, who is compelled by the necessity of his nature to be a partisan, lending effectual aid to Socrates; there is Critias assuming the tone of impartiality; Callias, here as always inclining to the Sophists, but eager for any intellectual repast; Prodicus, who finds an opportunity for displaying his distinctions of language, which are valueless and pedantic, because they are not based on dialectic; Hippias, who has previously exhibited his superficial knowledge of natural philosophy, to which, as in both the Dialogues called by his name, he now adds the profession of an interpreter of the Poets. The two latter personages have been already damaged by the mock heroic description of them in the introduction. It may be remarked that Protagoras is consistently presented to us throughout as the teacher of moral and political virtue; there is no allusion to the theories of sensation which are attributed to him in the Theaetetus and elsewhere, or to his denial of the existence of the gods in a well-known fragment ascribed to him; he is the religious rather than the irreligious teacher in this Dialogue. Also it may be observed that Socrates shows him as much respect as is consistent with his own ironical character; he admits that the dialectic which has overthrown Protagoras has carried himself round to a conclusion opposed to his first thesis. The force of argument, therefore, and not Socrates or Protagoras, has won the day.

But is Socrates serious in maintaining (1) that virtue cannot be taught; (2) that the virtues are one; (3) that virtue is the knowledge of pleasures and pains present and future? These propositions to us have an appearance of paradox—they are really moments or aspects of the truth by the help of which we pass from the old conventional morality to a higher conception of virtue and knowledge. That virtue cannot be taught is a paradox of the same sort as the profession of Socrates that he knew nothing. Plato means to say that virtue is not brought to a man, but must be drawn out of him; and cannot be taught by rhetorical discourses or citations from the poets. The second question, whether the virtues are one or many, though at first sight distinct, is really a part of the same subject; for if the virtues are to be taught, they must be reducible to a common principle; and this common principle is found to be knowledge. Here, as Aristotle remarks, Socrates and Plato outstep the truth—they make a part of virtue into the whole. Further, the nature of this knowledge, which is assumed to be a knowledge of pleasures and pains, appears to us too superficial and at variance with the spirit of Plato himself. Yet, in this, Plato is only following the historical Socrates as he is depicted to us in Xenophon's Memorabilia. Like Socrates, he finds on the surface of human life one common bond by which the virtues are united,—their tendency to produce happiness,—though such a principle is afterwards repudiated by him.

It remains to be considered in what relation the Protagoras stands to the other Dialogues of Plato. That it is one of the earlier or purely Socratic works—perhaps the last, as it is certainly the greatest of them—is indicated by the absence of any allusion to the doctrine of reminiscence; and also by the different attitude assumed towards the teaching and persons of the Sophists in some of the later Dialogues. The Charmides, Laches, Lysis, all touch on the question of the relation of knowledge to virtue, and may be regarded, if not as preliminary studies or sketches of the more important work, at any rate as closely connected with it. The Io and the lesser Hippias contain discussions of the Poets, which offer a parallel to the ironical criticism of Simonides, and are conceived in a similar spirit. The affinity of the Protagoras to the Meno is more doubtful. For there, although the same question is discussed, 'whether virtue can be taught,' and the relation of Meno to the Sophists is much the same as that of Hippocrates, the answer to the question is supplied out of the doctrine of ideas; the real Socrates is already passing into the Platonic one. At a later stage of the Platonic philosophy we shall find that both the paradox and the solution of it appear to have been retracted. The Phaedo, the Gorgias, and the Philebus offer further corrections of the teaching of the Protagoras; in all of them the doctrine that virtue is pleasure, or that pleasure is the chief or only good, is distinctly renounced.

Thus after many preparations and oppositions, both of the characters of men and aspects of the truth, especially of the popular and philosophical aspect; and after many interruptions and detentions by the way, which, as Theodorus says in the Theaetetus, are quite as agreeable as the argument, we arrive at the great Socratic thesis that virtue is knowledge. This is an aspect of the truth which was lost almost as soon as it was found; and yet has to be recovered by every one for himself who would pass the limits of proverbial and popular philosophy. The moral and intellectual are always dividing, yet they must be reunited, and in the highest conception of them are inseparable. The thesis of Socrates is not merely a hasty assumption, but may be also deemed an anticipation of some 'metaphysic of the future,' in which the divided elements of human nature are reconciled.