Thrasymachus, Glaucon and the Ring of Gyges

The Republic begins with a challenge: why should anyone be just? In Book 1, the Sophist Thrasymachus claims that justice is simply 'the advantage of the stronger', since rulers make laws to serve themselves, and that injustice on a large scale pays better. In Book 2, Glaucon sharpens the challenge with a thought experiment. A shepherd named Gyges finds a ring that makes him invisible; he uses it to seduce the queen, kill the king and seize power.

Glaucon argues that anyone with such a ring would behave the same way, so people are just only because they fear being caught. He asks Socrates to prove that justice is worth having for its own sake, even with no reward. The rest of the Republic is Plato's answer. The challenge is powerful because it asks whether morality is genuine or merely a social bargain backed by punishment.