SOCRATES: And now, let me give a parable to show how far our nature is enlightened or unenlightened. Imagine human beings living in an underground cave with an opening upward towards the light, which filters into the depths of the cave. These human beings have been here since birth, and their legs and necks have been chained so that they cannot move. They can only see what is directly in front of them, since they are prevented by the chains from turning their heads to either side. At a distance above and behind them is a raised path. And if you look closely, you will see a low wall built along the path, like the screen used by marionette players to conceal themselves from the audience while they show their puppets.
GLAUCON: I see.
SOCRATES: And do you see men passing behind the wall carrying all sorts of objects, such as figures of animals and humans made of wood, stone, and various materials, which they are holding above the wall? Some of the men carrying these objects are talking, while others are silent.
GLAUCON: You have shown me a strange image, and these are strange prisoners.
SOCRATES: They are similar to us. For, initially, how could they see anything but their own shadows, or the shadows of each other, which the fire projects on the wall of the cave in front of them?
GLAUCON: That is true. How could they see anything but the shadows if they were never allowed to turn their heads?
SOCRATES: And wouldn't they see only the shadows of the objects that are being carried by the men?
SOCRATES: And if these prisoners were able to talk to each other, would they not suppose that the words they used referred only to the shadows that they saw on the wall in front of them?
GLAUCON: Of course.
SOCRATES: And if one of these prisoners was able at last to free himself, and explore to the upper world, would he understand what he saw?
GLAUCON: Not immediately.
SOCRATES: He would have to grow accustomed to the sights of the upper world. First he would be able to see the shadows best, next the reflections of men and other things in the water, and then the things themselves. Afterwards he would be able to gaze upon the light of the moon, the stars, and the spangled heaven. Would it not be easier at first for him to look upon the sky and the stars by night than upon the sun or the light of the sun by day?
SOCRATES: Last of all he would be able to see the sun, not merely as it is reflected in the water, but in its true nature and in its own proper place.
SOCRATES: He will then begin to conclude that it is the sun which causes the seasons and the years, which is the guardian of everything in the visible world, and which, in a certain way, is the cause of all the things that he and his fellows have formerly seen.
GLAUCON: It is evident that he would first see the sun and then reason about it.
SOCRATES: And when he remembered his old habituation, and the wisdom of the cave and of his fellow-prisoners, do you not suppose that he would be happy about his change and pity those who were still prisoners?
GLAUCON: Certainly he would.
SOCRATES: And if they were in the habit of honoring those who could most quickly observe the passing shadows and decide which of them went before others, which came after, which occurred simultaneously--being therefore best able to draw conclusions about the future--do you think that he would care for such honors or envy the possessors of them? Would he not say with Homer, "Better to be the poor servant of a poor master," and to endure anything, rather than think as they do and live after their manner?
GLAUCON: Yes, I think that he would rather suffer anything than accept these false notions and live in this miserable manner.
SOCRATES: Indeed, imagine what it would be like for him to come suddenly out of the sun and to return to his old place in the cave. Would he not be certain to have his eyes full of darkness?
GLAUCON: Most assuredly.
SOCRATES: And while his eyes were filled with darkness and his sight still weak (and the time needed to become re-accustomed to the cave might be very considerable), if there were a contest in which he had to compete in measuring the shadows with the prisoners who had never been out of the cave, would he not be ridiculous? Men would say of him that his ascent and descent had destroyed his eyesight, and thus that it was better not even to think of ascending. And if they caught anyone trying to free another and lead him up to the light, they would put the offender to death.
GLAUCON: Without question.
SOCRATES: You may append this entire allegory, dear Glaucon, to what I have said before. The prisonhouse or cave is the world of sight; the light of the fire within the cave is the sun. And you will not misapprehend me if you interpret the journey upwards to be the ascent of the soul into the intelligible world, which, at your request, I have described. Only God knows whether or not my description is accurate. But whether true or false, my opinion is that in the world of knowledge the Form of the Good appears last of all, and is seen only with an effort. When seen, however, it can only lead us to the conclusion that it is the universal author of all things beautiful and right, that it is the origin of the source of light in the visible world, and the immediate source of reason and truth in the intelligible world. Without having seen the Form of Good and having fixed his eye upon it, one will not be able to act wisely either in public affairs or in private life.
GLAUCON: I agree, as far as I am able to understand you.