Plato in the Republic

In The Republic, Plato, speaking through his teacher Socrates, sets out to answer two questions. What is justice? Why should we be just? Book I sets up these challenges. The interlocutors engage in a Socratic dialogue similar to that found in Plato’s earlier works. While among a group of both friends and enemies, Socrates poses the question, “What is justice?” He proceeds to refute every suggestion offered, showing how each harbors hidden contradictions. Yet he offers no definition of his own, and the discussion ends in aporia—a deadlock, where no further progress is possible and the interlocutors feel less sure of their beliefs than they had at the start of the conversation. In Plato’s early dialogues, aporia usually spells the end. The Republic moves beyond this deadlock. Nine more books follow, and Socrates develops a rich and complex theory of justice.

When Book I opens, Socrates is returning home from a religious festival with his young friend Glaucon, one of Plato’s brothers. On the road, the three travelers are waylaid by Adeimantus, another brother of Plato, and the young nobleman Polemarchus, who convinces them to take a detour to his house. There they join Polemarchus’s aging father Cephalus, and others. Socrates and the elderly man begin a discussion on the merits of old age. This discussion quickly turns to the subject of justice.

Cephalus, a rich, well-respected elder of the city, and host to the group, is the first to offer a definition of justice. Cephalus acts as spokesman for the Greek tradition. His definition of justice is an attempt to articulate the basic Hesiodic conception: that justice means living up to your legal obligations and being honest. Socrates defeats this formulation with a counterexample: returning a weapon to a madman. You owe the madman his weapon in some sense if it belongs to him legally, and yet this would be an unjust act, since it would jeopardize the lives of others. So it cannot be the case that justice is...