PLATO'S ALLEGORY OF
One of the most famous thought experiments in the history of philosophy is Plato's Allegory of the Cave. In Book VII of Republic, Socrates asks Glaucon to imagine prisoners “living in an underground, cave-like dwelling, with an entrance a long way up, which is both open to the light and as wide as the cave itself. They’ve been there since childhood, fixed in the same place, with their necks and legs fettered, able to see only in front of them, because their bonds prevent them from turning their heads around” (VII, 514). They stare at a cave wall on which are projected images. These images are cast from carved figures (puppets) illuminated by a fire and carried by people on a parapet above and behind the prisoners. They see nothing of themselves and one another. They only see “the shadows that the fire casts on the wall in front of them” (515).
If one of the prisoners is released from his chains “and suddenly compelled to stand up, turn his head, walk, and look up toward the light, he would first see the puppets and the fire." If he is “dragged away from there by force,” up the rough steep path and out of the cave and into the sunlight he would need time to get adjusted. “At first he’d see shadows most easily, then images of men and other things in water, then the things themselves… Finally, he’d be able to see the sun, not images of it in water or some alien place, but the sun itself, in its own place, and be able to study it” (516).
Here is a brilliant animated video that powerfully displays Plato's famous allegory: