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.