In an interview on Moral Philosophy

You have chosen mostly non-philosophical books.

I teach philosophy, especially ethics. This could be a list of books by the great philosophers, but only one of them fits that description. This is because the questions I am most interested in are about how we should live and by what values. My list reflects the obvious point that many people who are not philosophers have written books important for this.

But you have gone for Plato’s Republic.

The only philosophy book I am choosing. It contains a tremendous amount of nonsense about what the ideal society would be like. But is an unmissable book because of Socrates. He invented the method of doing and teaching philosophy that has never been improved on. His persistent questions forced people to spell out their beliefs more fully and precisely, often unearthing beliefs they hardly knew they had. He would then challenge them with counter-examples, putting pressure on beliefs by pointing out unwelcome consequences they had. This questioning is often both intimidating and liberating. Those of us who teach philosophy aim (not always successfully) for the liberation without the intimidation.

Some of Socrates’ opponents in The Republic challenge him as to whether there is any reason to be moral, apart from social pressures. They use a simple but brilliant thought experiment. Would you have any reason to avoid wrongdoing if you had a ring that made you invisible, so there was no chance of getting caught? It is not the answers given to this and the other questions in the book, but the absolutely fundamental challenges of the questions themselves.