Three definitions of justice, broken

Socrates has gone down to the Piraeus with Glaucon for a torchlight festival of a Thracian goddess. Heading back to the city, they are stopped by Polemarchus, who sends a slave running ahead with a half-joking order to detain them. There are too many of us, he says when he catches up; you cannot fight us all. Socrates, charmed, agrees to stay. They go to Polemarchus's house, where old Cephalus is just back from a sacrifice and the household is preparing for the night.

Cephalus is gracious, almost sentimental, about old age. Socrates asks him what justice is. He answers easily: paying your debts and telling the truth. Socrates objects with a single example — a friend lends you a weapon, and then comes asking for it back while in a rage; do you return it? — and Cephalus, before the argument can deepen, slips out to attend a sacrifice. His son Polemarchus inherits the conversation and tries again: justice is helping friends and harming enemies. Socrates dismantles this one too. We are not always sure who our friends are. Helping a person who turns out to be an enemy serves injustice. Harm is itself a form of injustice. The argument unwinds.

Then Thrasymachus loses his patience. He has been crouched and listening, furious, for some time. He breaks in with the answer he has been holding back: justice is nothing more than the advantage of the stronger. Whoever rules makes laws that serve themselves, and calls obedience to those laws "justice." Socrates pulls the argument apart over the rest of the book — by the end, Thrasymachus has agreed, against his will, that the just life is happier than the unjust. He is not convinced; he is only outmaneuvered. Book One ends with the ground cleared and no definition standing. The real dialogue is about to begin.