The Republic

The sharp-tongued Thrasymachus argues that justice is simply whatever benefits the stronger, and Plato's brothers Glaucon and Adeimantus press Socrates further, using the story of a ring that makes its wearer invisible to ask whether anyone would be just if they could never be caught. To answer, Socrates builds an imaginary ideal city, with workers, guardians and rulers, and compares it to the human mind, which he divides into reason, spirit and appetite.

The dialogue covers education, art, censorship, the equality of men and women among the guardians, and the famous claim that philosophers should rule. It contains the Allegory of the Cave, in which prisoners mistake shadows for reality, and the theory that the world we perceive is only a reflection of unchanging Forms. Many of its proposals, such as abolishing private family life for the rulers, have troubled readers for centuries, and the book has been praised and attacked ever since. A good introduction and notes help modern readers.

Challenging but rewarding, a book whose questions about justice, power, education and truth still shape debates today and reward slow, careful reading. About 480 pages in the Penguin Classics translation by Desmond Lee.