A bunch of cavemen are kept chained together against a wall, only able to see a wall across from them. There is a fire they cannot see behind them, and every day people parade shadow puppets of figures on the wall in front of them. One day, one of the prisoners is set free. They turn around, and see the light. It hurts their eyes. They observe that the shapes they have seen on the wall their whole life were fake. They would then turn around and go back to what they knew, rather than trying to perceive this new revelation.

If a prisoner was freed and dragged up to the surface of the world, the prisoner would be angry and the sun would blind them. But then, they would get used to the light. They would first see shadows, and then the reflections of people and things in the water, and then see the people and things themselves. Next, they would be able to see the moon and stars at night, and finally they could perceive the sun itself.

Only after they see the sun, Plato believed, could they begin to reason about it and what it does.

The prisoner would see the outside world as superior, and return to the cave to tell their fellow prisoners such. But they would be blinded by the darkness after having been in the sun, and the other prisoners, seeing their blindness and how the journey had apparently harmed them, would not follow them and would in fact try to kill them for trying to bring them out of the cave and into reality.

The cavemen represent most people, observing reality with their senses. The escaped prisoner represent a philosopher, on their journey to perceive reality as it is and share their revelation with the common people. The above-ground world represents a higher form of reality, that one must go on a difficult journey to perceive.