The 'Chalcedonian giant,' Thrasymachus, of whom we have already heard in the Phaedrus, is the personification of the Sophists, according to Plato's conception of them, in some of their worst characteristics. He is vain and blustering, refusing to discourse unless he is paid, fond of making an oration, and hoping thereby to escape the inevitable Socrates; but a mere child in argument, and unable to foresee that the next 'move' (to use a Platonic expression) will 'shut him up.' He has reached the stage of framing general notions, and in this respect is in advance of Cephalus and Polemarchus. But he is incapable of defending them in a discussion, and vainly tries to cover his confusion with banter and insolence. Whether such doctrines as are attributed to him by Plato were really held either by him or by any other Sophist is uncertain; in the infancy of philosophy serious errors about morality might easily grow upthey are certainly put into the mouths of speakers in Thucydides; but we are concerned at present with Plato's description of him, and not with the historical reality. The inequality of the contest adds greatly to the humour of the scene. The pompous and empty Sophist is utterly helpless in the hands of the great master of dialectic, who knows how to touch all the springs of vanity and weakness in him. He is greatly irritated by the irony of Socrates, but his noisy and imbecile rage only lays him more and more open to the thrusts of his assailant. His determination to cram down their throats, or put 'bodily into their souls' his own words, elicits a cry of horror from Socrates. The state of his temper is quite as worthy of remark as the process of the argument. Nothing is more amusing than his complete submission when he has been once thoroughly beaten. At first he seems to continue the discussion with reluctance, but soon with apparent goodwill, and he even testifies his interest at a later stage by one or two occasional remarks. When attacked by Glaucon he is humorously protected by Socrates 'as one who has never been his enemy and is now his friend.' From Cicero and Quintilian and from Aristotle's Rhetoric we learn that the Sophist whom Plato has made so ridiculous was a man of note whose writings were preserved in later ages. The play on his name which was made by his contemporary Herodicus (Aris. Rhet.), 'thou wast ever bold in battle,' seems to show that the description of him is not devoid of verisimilitude.
When Thrasymachus has been silenced, the two principal respondents, Glaucon and Adeimantus, appear on the scene: here, as in Greek tragedy (cp. Introd. to Phaedo), three actors are introduced. At first sight the two sons of Ariston may seem to wear a family likeness, like the two friends Simmias and Cebes in the Phaedo. But on a nearer examination of them the similarity vanishes, and they are seen to be distinct characters. Glaucon is the impetuous youth who can 'just never have enough of fechting' (cp. the character of him in Xen. Mem. iii. 6); the man of pleasure who is acquainted with the mysteries of love; the 'juvenis qui gaudet canibus,' and who improves the breed of animals; the lover of art and music who has all the experiences of youthful life. He is full of quickness and penetration, piercing easily below the clumsy platitudes of Thrasymachus to the real difficulty; he turns out to the light the seamy side of human life, and yet does not lose faith in the just and true. It is Glaucon who seizes what may be termed the ludicrous relation of the philosopher to the world, to whom a state of simplicity is 'a city of pigs,' who is always prepared with a jest when the argument offers him an opportunity, and who is ever ready to second the humour of Socrates and to appreciate the ridiculous, whether in the connoisseurs of music, or in the lovers of theatricals, or in the fantastic behaviour of the citizens of democracy. His weaknesses are several times alluded to by Socrates, who, however, will not allow him to be attacked by his brother Adeimantus. He is a soldier, and, like Adeimantus, has been distinguished at the battle of Megara (anno 456?)The character of Adeimantus is deeper and graver, and the profounder objections are commonly put into his mouth. Glaucon is more demonstrative, and generally opens the game. Adeimantus pursues the argument further. Glaucon has more of the liveliness and quick sympathy of youth; Adeimantus has the maturer judgment of a grownup man of the world. In the second book, when Glaucon insists that justice and injustice shall be considered without regard to their consequences, Adeimantus remarks that they are regarded by mankind in general only for the sake of their consequences; and in a similar vein of reflection he urges at the beginning of the fourth book that Socrates fails in making his citizens happy, and is answered that happiness is not the first but the second thing, not the direct aim but the indirect consequence of the good government of a State. In the discussion about religion and mythology, Adeimantus is the respondent, but Glaucon breaks in with a slight jest, and carries on the conversation in a lighter tone about music and gymnastic to the end of the book. It is Adeimantus again who volunteers the criticism of common sense on the Socratic method of argument, and who refuses to let Socrates pass lightly over the question of women and children. It is Adeimantus who is the respondent in the more argumentative, as Glaucon in the lighter and more imaginative portions of the Dialogue. For example, throughout the greater part of the sixth book, the causes of the corruption of philosophy and the conception of the idea of good are discussed with Adeimantus. Glaucon resumes his place of principal respondent; but he has a difficulty in apprehending the higher education of Socrates, and makes some false hits in the course of the discussion. Once more Adeimantus returns with the allusion to his brother Glaucon whom he compares to the contentious State; in the next book he is again superseded, and Glaucon continues to the end.