The Republic is Plato’s most famous work. It focuses on a crucial ethical question: is justice good in itself, or is the fear of retribution our only reason to be just? The question is examined through a conversation between Plato’s teacher, Socrates, and a number of other characters, including Plato’s brother Glaucon. Glaucon uses the story of Gyges to put the question in its starkest terms: if you had the opportunity to grab wealth and power at everyone else’s expense, without any chance of retribution, what reason could there be to pass it up?

The Republic, like most of Plato’s works, is written as a dialogue. This is not simply a matter of literary style - it goes to the heart of Plato’s views about the practice of philosophy. You cannot obtain philosophical knowledge, Plato thought, by accepting the pronouncements of expert philosophers. You need to do philosophy - to engage in debate, examining the questions, looking for objections, and puzzling things out for yourself. The role of the teacher is not to impart knowledge, but to help the student to generate and criticise his or her own ideas. This conception of education has been crucial in the philosophy of education and in the teaching of philosophy since Plato’s time.

The Republic, admittedly, is not the best example of this - the speeches are long and Socrates is allowed to present his views almost unchallenged. But Plato certainly does not intend his readers to turn off their critical faculties, but to engage with Socrates’ arguments in a spirit of joint inquiry.

Perhaps the most astounding feature of ...