In the cave behind them is a bright fire. Unknown to them there is a rampart as high as a man between the fire and them; and on the other side of this rampart are people perpetually passing to and fro carrying things on their heads. The shadows of these objects are cast on to the wall in front of the prisoners by the light of the fire, and the voices of the people carrying them are echoed back from this wall to the prisoners’ ears. Now, says Plato, the only entities that the prisoners ever perceive or experience in the whole of their existence are those shadows and those echoes. In these circumstances it would be natural for them to assume that shadows and echoes constitute all the reality there is; and it would be to this “reality,” and to their experiences of it, that all their talk would refer.
If one of the prisoners could shake off his chains, so cramped would he be by a lifetime of entrapment in the half-dark, that merely to turn around would be painful and awkward for him, and the fire would dazzle his eyes. He would find himself confused and uncomprehending, and would want to turn back again to face the wall of shadows, the reality he understood. If he were dragged up out of the cave altogether into the world of blazing sunlight he would be blinded and bewildered, and it would be a long time before he was able to see or understand anything. But then, once he was used to being in the upper world, if he were to return to the cave he would be temporarily blinded again, this time by the darkness. And everything he said to the prisoners about his experiences would be unintelligible to those people whose language had reference only to shadows and echoes.
The way to begin understanding this allegory is to see us human beings as imprisoned in our own bodies, with only other such prisoners for company, and all of us unable to discern the real selves of one another, or even our own real selves. Our direct experience is not of reality, but what is in our minds.