In a cave there were some men, chained from childhood so that they could not turn their heads. They faced a wall, and behind them a fire burned. Between the fire and the prisoners others walked, carrying figures of men and beasts, so that shadows fell upon the wall.

To the prisoners, these shadows were the only reality they knew. They named them, measured them, argued about them, yet they had never seen the true forms.

One day a man was freed. At first he turned and saw the fire, and the brightness pained him. Slowly he began to see the figures casting the shadows. At last he was led out of the cave, into the sunlight. There he saw the world as it truly was, and he understood that all the while he and his companions had lived in darkness, mistaking faint outlines for truth.