Plot
Imagine prisoners, who have been chained since their childhood deep inside a cave: not only are their limbs immobilized by the chains; their heads are chained in one direction as well, so that their gaze is fixed on a wall.
Behind the prisoners is an enormous fire, and between the fire and the prisoners is a raised walkway, along which statues of various animals, plants, and other things are carried by people. The statues cast shadows on the wall, and the prisoners watch these shadows. When one of the statue-carriers speaks, an echo against the wall causes the prisoners to believe that the words come from the shadows.
The prisoners engage in what appears to us to be a game: naming the shapes as they come by. This, however, is the only reality that they know, even though they are seeing merely shadows of images. They are thus conditioned to judge the quality of one another by their skill in quickly naming the shapes and dislike those who play poorly.
Suppose a prisoner is released and compelled to stand up and turn around. At that moment his eyes will be blinded by the sunlight coming into the cave from its entrance, and the shapes passing by will appear less real than their shadows.
The last object he would be able to see is the sun, which, in time, he would learn to see as the object that provides the seasons and the courses of the year, presides over all things in the visible region, and is in some way the cause of all these things that he has seen.
(This part of the allegory, incidentally, closely matches Plato's metaphor of the sun which occurs near the end of The Republic, Book VI.)[1]
Once enlightened, so to speak, the freed prisoner would not want to return to the cave to free "his fellow bondsmen," but would be compelled to do so. Another problem lies in the other prisoners not wanting to be freed: descending back into the cave would require that the freed prisoner's eyes adjust again, and for a time, he would be one of the ones identifying shapes on the wall. His eyes would be swamped by the darkness, and would take time to become acclimated. Therefore, he would not be able to identify the shapes on the wall as well as the other prisoners, making it seem as if his being taken to the surface completely ruined his eyesight. (The Republic bk. VII, 516b-c; trans. Paul Shorey).[2]
[edit] Interpretation
Socrates himself interprets the allegory (beginning at 517b): "This image then [the allegory of the cave] we must apply as a whole to all that has been said"—i.e. the preceding analogy of the divided line and metaphor of the sun.
It has been up to scholarly debate in 20th century how exactly these three sequential comparisons can be coherently bound together. The main problems arise from the allegory of the cave having three cognitive stages and the divided line having four of them, where the first division (shadows, reflections) seems not to be needed to apply to the cave and is hard to be interpreted ontologically, i.e. in the manner of the cave at all. The metaphor of the sun seems to assert that from seeing things in the light of the sun we can raise to seeing ideas in the light of the Good, while in the cave it is not evident that it can not be done without helping and forcing prisoners to look at the light.
[edit] Plato's own remarks on the allegory
In particular, Plato likens "the region revealed through sight"—the ordinary objects we see around us—"to the habitation of the prison, and the light of the fire in it to the power of the sun. And if you assume the ascent and the contemplation of the things above is the soul's ascension to the intelligible region, you will not miss my surmise...[M]y dream as it appears to me is that in the region of the known the last thing to be seen and hardly seen is the idea of good, and that when seen, it must point us to the conclusion that this is indeed the cause for all things of all that is right and beautiful, giving birth in the visible world to light, and l the author of light and itself in the intelligible world being the authentic source of truth and reason..." (517b-c). After "returning from divine contemplations to the petty miseries of men", one is apt to cut "a sorry figure" if, "while still blinking through the gloom, and before he has become sufficiently accustomed to the environing darkness, he is compelled in courtrooms or elsewhere to contend about the shadows of justice or the images that cast the shadows and to wrangle in debate about the notions of these things in the minds of those who have never seen justice itself?" (517d-e)
[edit] Different grounds for interpretation
One can also choose whether the meaning of allegory is epistemological or ontological, i.e. are the shadows to be correlated with things in our world of sight, the things in the cave with mathematical entities, and things outside the cave with ideas or should we just concentrate on the cognitive stages. It has been claimed that a purely epistemological view is foreign to Greek tradition (especially Plato), which holds that the reading should bring ontological statements within.
Besides cognitive interpretations the allegory has also clear political implications, for example the fourth stage of returning to cave to help fellow-prisoners. Also the play of shadows can be interpreted as political juggling over citizens heads and this seems to be natural because of the whole context of The Republic. Since the highest knowledge in the allegory is The Good then the interpretation should bring together at least ethical allusions about attaining virtues.
However, Plato himself introduces the allegory of the cave letting Socrates say that it is about education (paideia) and miseducatedness (apaideusia).
[edit] Movements between stages
Since allegory is by Socrates' words about education, it should be interpreted from the viewpoint of conditions for taking steps toward higher stages, i.e. conditions for education.
There are four steps described: (1) prisoners who think that shadows are reality; (2) prisoners who are freed and forced to look at the things that are used to cast shadows on the wall and do not recognize these as sources for shadows; (3) prisoners who are freed and dragged along to the outside of cave; (4) free men returning to the cave to former fellow-prisoners.
Step (3) has also four sub-steps of looking at (a) shadows, (b) things that cast shadows, (c) heavenly bodies, (d) sun as the source and guarantee of all the things outside cave.
Substeps beneath step (3) cohere notably with analogy of the divided line. Confrontation between cave and outside can be explained by metaphor of sun, but there is one major difference: in the cave one cannot deduce from whatever position that burning artificial light and things that are carried are the source for shadows. Metaphor of the sun argues but that this kind of deduction is possible.
All the steps have their proper interpretation from ontological, epistemological and ethical point of view. The cave is dark.