In defending the view that justice is the advantage of the stronger, Thrasymachus puzzlingly claims that rulers never err and that any practitioner of a skill or expertise (τέχνη) is infallible. In what follows, Socrates offers a number of arguments directed against Thrasymachus’ views concerning the nature of skill, ruling, and justice. Commentators typically take a dim view of both Thrasymachus’ claims about skill (which are dismissed as an ungrounded and purely ad hoc response to Socrates’ initial criticisms) and Socrates’ (...) latter arguments (which are deemed extremely weak). In this paper, I clarify Thrasymachus’ views (and those of several other ancients) concerning qua locutions and the nature of skill and ability and I reconstruct Socrates’ arguments against Thrasymachus’ views concerning skill and justice. I argue that Thrasymachus’ views are not ungrounded or ad hoc and that Socrates’ arguments are rather different (and significantly stronger) than often supposed. (shrink)