Thrasymachus - in Plato

In Plato

Thrasymachus' current importance derives mainly from his being a character in The Republic. He is noted for his unabashed, even reckless, defense of injustice and for his famous blush at the end of Book 1, after Socrates has tamed him. The meaning of this blush, like that of Socrates' statement in Book 6 that he and Thrasymachus "have just become friends, though we weren't even enemies before" (498c), is a source of some dispute.

There is a long philosophical tradition of exploring what exactly Thrasymachus meant in Republic I, and of taking his statements as a coherent philosophical assertion, rather than as Plato's straw man.

In the Republic I, Thrasymachus violently disagreed with the outcome of Socrates' discussion with Polemarchus about justice. Demanding payment before speaking, he claims that "justice is the advantage of the stronger" (338c) and that "injustice, if it is on a large enough scale, is stronger, freer, and more masterly than justice'" (344c). Socrates counters by forcing him to admit that there is some standard of wise rule — Thrasymachus does claim to be able to teach such a thing — and then arguing that this suggests a standard of justice beyond the advantage of the stronger. The rest of the dialogue is occasioned by Glaucon's dissatisfaction with Socrates' refutation.

His name means fierce fighter, which may have influenced his role in the dialogue.

In Leo Strauss's interpretation, Thrasymachus and his definition of justice represent the city and its laws, and thus are in a sense opposed to Socrates and to philosophy in general. As an intellectual, however, Thrasymachus shared enough with the philosopher to potentially act to protect philosophy in the city.