The Cambridge Companion to Plato's Republic

Plato gives depth to character by writing in three dimensions. In the Republic's main speakers - Socrates and his two younger friends Glaucon and Adeimantus, Plato's real-life brothers - Plato characterizes fully human beings. First to the reader's sight are arguers and arguments, so the logical dimension of character becomes most immediately visible. But these men are not mere talking heads or disembodied minds. They have about them the smell of mortality, with their individual histories, personalities, and commitments. It is not just a question of what arguments are made, but of what sort of man would make a particular argument, or accept it, or long for it. Indeed, Socrates virtually begins his conversation with the brothers by saying he would respond to their arguments differently if he had a different view of their character (368a-b). We catch something of this ethical and psychological dimension of Plato's writing when, for example, Socrates must playfully defend himself in a mock trial, reminding us that one day he will be tried in deadly earnest; when Glaucon lets slip an erotic streak he would prefer not to own; when Adeimantus' limitations are implicitly revealed by having Socrates go beyond them in conversation with his more brilliant brother.