Having presented us with the Analogy of the Sun and the Analogy of the Line, Socrates now in the conversation introduces the Allegory of the Cave. Socrates is here still trying to clarify the four levels of intellect, the two levels of belief, and the two levels of knowledge.
For this allegory, we are to imagine an underground Cave, whose entrance/exit leads upward to daylight. There are prisoners in the Cave who have been chained there since their childhood; they are chained to the ground and chained by their heads. They can see only the wall of the Cave in front of them. A fire is burning behind the prisoners; between the fire and the arrested prisoners, there is a walkway where people walk and talk and carry objects. The prisoners perceive only shadows of the people and things passing on the walkway; the prisoners hear echoes of the talk coming from the shadows. The prisoners perceive the shadows and echoes as reality.
If we unchain one of the prisoners and make him turn around, he would be frightened, pained by new physical movement, dazzled by the fire, unable at first to see. When he is told that the people and things he now perceives are more real than the shadows, he will not believe it. He will want to return to his old perceptions of the shadows as reality. When we drag him out of the Cave and into the World of Day, the sun will blind him. But he will gradually see the stars and the moon; he will then be able to see shadows in the daylight thrown by the sun; then he will see objects in the full light of day. The sun makes this new perception possible. If we took the prisoner back into the Cave, into his old world, he would not be able to function well in his old world of shadows.
For the allegory, the Cave corresponds to the realm of belief; the World of Day corresponds to the realm of knowledge. The sun stands for the Form of Goodness itself. If the prisoner were to be returned to the Cave, his old fellows would not believe his experiences, since they have always been imprisoned in their world, the Cave.
Thus, allegorically, we must release the prisoners from their Cave: We must give the Guardians the experience of education so that they can become the philosopher-kings of the Ideal State, because they will be able to know the Forms and, finally, Goodness itself.
But it is not enough that the prisoner, freed, now possesses knowledge. He must be returned to the Cave to enlighten his erstwhile fellows about the knowledge he now perceives.
Glaucon objects: He argues that for the enlightened prisoner to return to the Cave would make him unhappy. It would be a lot of work to lead his fellows into the light of a kind of new dawn of knowledge. Socrates here reminds us, again, that the business of rulers is not to make themselves happy; their happiness is to be realized in the happiness of every citizen in the Ideal State.
