Deep in Book VII of Plato’s Republic, Socrates describes prisoners chained inside a cave, mistaking shadows cast on a wall by firelight for reality itself. They name the shadows, debate them and develop expertise about them. The prisoners are completely, sincerely wrong, and they have no idea. The cave isn’t a place of stupidity, it’s a place of convincing, well-organised illusion. But Plato’s real interest wasn’t the cave, it was in the periagoge – a Greek word meaning the turning of the soul a