"The Allegory of the Cave" by Plato

Imagine there are men living at the bottom of an underground cave whose entrance is a long passageway that rises up through the ground to the light outside. They have been there since childhood and have their legs and necks chained so that they cannot move. Their heads are held by the chains so that they must sit facing the back wall of the cave and cannot turn their heads to look up through the entrance behind them. At some distance behind them, up nearer the entrance to the cave, a fire is burning, and objects pass in front of he fire so that they cast their shadows on the back wall where the prisoners see the moving shadows projected as if on a screen. All kinds of objects are paraded before the fire, including statues of men and animals whose shadows dance on the wall in front of the prisoners.

Those prisoners are like ourselves. The prisoners see nothing of themselves or each other except for the shadows each one's body casts on the back wall of the cave. Similarly, they see nothing of the objects behind them, except for their shadows moving on the wall.

Now imagine the prisoners were able to talk with each other, and suppose their voices echoed off the wall so that the voices seemed to be coming from their own shadows. Then wouldn't they talk and refer to these shadows as if the shadows were real? For the prisoners, reality would consist of nothing but the shadows. But next imagine that one of the prisoners was freed from is chains. Suppose he was suddenly forced to stand up and face toward the entrance of the cave and then forced to walk up toward the burning fire. The movement would be painful, and the glare from the fire would blind him so that he would not see clearly the real objects whose shadows he used to watch. What would he think if someone explained that everything he had seen before was an illusion and that now he was nearer to reality and that his vision was actually clearer?

Imagine he was then shown the objects that had cast their shadows on the wall and he was asked to name each one - wouldn't he be at a complete loss? Wouldn't he think the shadows he saw before were more true than these objects?

Next imagine he was forced to look straight at the burning light. His eyes would hurt and the pain would make him turn away and try to escape back to things he could see more easily, convinced that they really were more real than the new things he was being shown.

But suppose that once more someone takes him and drags him up the steep and rugged ascent from the cave and forces him out into the full light of the sun. Wouldn't he suffer greatly and be furious at being dragged upward? As he approaches the light his eyes will be dazzled and he won't be able to see any of that world we ourselves call reality. Little by little he will have to get used to looking at the upper world. At first he will see shadows on the ground best, next perhaps the reflections of men and other objects in water, and then maybe the objects themselves. After this he would find it easier to gaze at the light of the moon and the stars in the night sky than to look at the daylight sun and its light. Last of all he will be able to look at the sun and contemplate its nature - not as it appears reflected in water but as it is in itself and in its own domain. He would come to the conclusion that the sun produces the seasons and the years and that it controls everything in the visible world. He will understand that it is in a way the cause of everything that he and his fellow prisoners used to see.

Suppose the released prisoner now recalled the cave and what passed for wisdom among his fellows there. Wouldn't he be happy about his new situation and feel sorry for them? They might have been in the habit of honouring those among themselves who were quickest to make out the shadows and those who could remember which usually came before others so that they were best at predicting the course of the shadows. Would he care anything for such honours and glories or would he envy those who won them? Wouldn't he rather endure anything than go back to thinking and living like they did?

Finally, imagine that the released prisoner was taken from the light and brought back into the cave to his old seat. His eyes would be full of darkness. Now he would have to compete in discerning the shadows with the prisoners who had never left the cave while his own eyes were still dim. Wouldn't he appear ridiculous? Men would say of him that he had gone up and had come back down with his eyesight ruined and that it was better not even to think of ascending. In fact, if they caught anyone trying to free them and lead them up to the light, they would try to kill him.

I say, now, that the prison is the world we see with our eyes; the light of the fire is like the power of our sun. And the climb upward out of the cave into the upper world is the ascent of the mind into the domain of true knowledge.