's fictional dialogue, Socrates
begins by describing a scenario in which what people take to be real would in fact be an illusion. He asks Glaucon to imagine a cave inhabited by prisoners who have been chained and held immobile since childhood: not only are their legs (but not arms) held in place, but their necks are also fixed, so they are compelled to gaze at a wall in front of them. Behind the prisoners is an enormous fire, and between the fire and the prisoners is a raised walkway, along which people walk carrying things on their heads "including figures of men and animals made of wood, stone and other materials". The prisoners cannot see the raised walkway or the people walking, but they watch the shadows cast by the men, not knowing they are shadows. There are also echoes off the wall from the noise produced from the walkway.
Socrates suggests the prisoners would take the shadows to be real things and the echoes to be real sounds created by the shadows, not just reflections of reality, since they are all they had ever seen or heard. They would praise as clever, whoever could best guess which shadow would come next, as someone who understood the nature of the world, and the whole of their society would depend on the shadows on the wall.