Plato, answered from the texts and cited to the page.
The cave allegory is the central image of the Republic's seventh book, and it is meant to show, in a single picture, what education is and what ignorance is — not as abstract definitions, but as conditions of the soul that can be felt. Imagine human beings chained since childhood in an underground dwelling, able to see only the wall before them.1
Behind them, a fire burns; between the fire and the prisoners, other figures carry objects whose shadows fall on the wall.2 The prisoners take these shadows for reality — they name them, they predict which will come next, they honor the one among them most skilled at reading the sequence.3 They have never seen the things that cast the shadows, let alone the fire, let alone the sun above.
When one prisoner is freed and turned toward the light, he is at first blinded and in pain.4 The things he now sees seem less real than the shadows he knew. He must be dragged upward — and the ascent is rough, and unwilling.5 Only gradually does he adjust: first shadows, then reflections in water, then the things themselves, then the sky at night, and at last the sun — which he comes to understand as the cause of everything visible, the source of the seasons, the governor of the whole.6
That sun is the Form of the Good. The ascent out of the cave is what I call dialektikē — dialectic — the journey through argument and away from sense perception toward the being of each thing itself, until the mind grasps the Good with understanding alone.7 The cave is not mere metaphor for ignorance in general; it maps precisely onto the four conditions I distinguish in the soul: eikasia (imaging), pistis (belief), dianoia (thought), and noēsis (understanding) — each corresponding to a region of the line, each sharing in clarity to the degree that its objects share in truth.8
What the allegory also shows, and what is harder to accept, is what happens when the philosopher returns. Coming back into the darkness, his eyes fill with shadow; he fumbles where the prisoners excel.9 They mock him, and if they could lay hands on the one who tried to lead them upward, they would kill him.10 You will recognize whose death that last detail commemorates.
The allegory, then, is simultaneously an epistemology, a psychology, and a political tragedy — all carried in one image, because some things the argument can only gesture at, and the image must carry the rest.
Imagine human beings living in an underground, cavelike 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.Complete Works, pp. 1161–1162
Also behind them, but on higher ground, there is a path... there are people along the wall, carrying all kinds of artifacts that project above it—statues of people and other animals, made out of stone, wood, and every material.Complete Works, pp. 1161–1162
Then the prisoners would in every way believe that the truth is nothing other than the shadows of those artifacts.Complete Works, pp. 1161–1162
When one of them was freed and suddenly compelled to stand up, turn his head, walk, and look up toward the light, he'd be pained and dazzled and unable to see the things whose shadows he'd seen before.Complete Works, pp. 1162–1163
And if someone dragged him away from there by force, up the rough, steep path, and didn't let him go until he had dragged him into the sunlight, wouldn't he be pained and irritated at being treated that way?Complete Works, pp. 1162–1163
And at this point he would infer and conclude that the sun provides the seasons and the years, governs everything in the visible world, and is in some way the cause of all the things that he used to see.Complete Works, pp. 1163–1164
whenever someone tries through argument and apart from all sense perceptions to find the being itself of each thing and doesn't give up until he grasps the good itself with understanding itself, he reaches the end of the intelligible.Complete Works, pp. 1176–1177
There are four such conditions in the soul, corresponding to the four subsections of our line: Understanding for the highest, thought for the second, belief for the third, and imaging for the last. Arrange them in a ratio, and consider that each shares in clarity to the degree that the subsection it is set over shares in truth.Complete Works, pp. 1161–1162
If this man went down into the cave again and sat down in his same seat, wouldn't his eyes—coming suddenly out of the sun like that—be filled with darkness?Complete Works, pp. 1163–1164
And, as for anyone who tried to free them and lead them upward, if they could somehow get their hands on him, wouldn't they kill him?Complete Works, pp. 1163–1164