structural:expansion, linguistic:paraphrasing
Book VI–VII: Allegories of the Sun, Divided Line, and Cave

The Allegory of the Cave primarily depicts Plato's distinction between the world of appearances and the 'real' world of the Forms. Just as visible objects must be illuminated in order to be seen, so must also be true of objects of knowledge if light is cast on them.

Plato imagines a group of people who have lived their entire lives as prisoners, chained to the wall of a cave in the subterranean so they are unable to see the outside world behind them. However a constant flame illuminates various moving objects outside, which are silhouetted on the wall of the cave visible to the prisoners. These prisoners, through having no other experience of reality, ascribe forms to these shadows such as either "dog" or "cat". Plato then goes on to explain how the philosopher is akin to a prisoner who is freed from the cave. The prisoner is initially blinded by the light, but when he adjusts to the brightness he sees the fire and the statues and how they caused the images witnessed inside the cave. He sees that the fire and statues in the cave were just copies of the real objects; merely imitations. This is analogous to the Forms. What we see from day to day are merely appearances, reflections of the Forms. The philosopher, however, will not be deceived by the shadows and will hence be able to see the 'real' world, the world above that of appearances; the philosopher will gain knowledge of things in themselves. At the end of this allegory, Plato asserts that it is the philosopher's burden to reenter the cave. Those who have seen the ideal world, he says, have the duty to educate those in the material world. Since the philosopher recognizes what is truly good only he is fit to rule society according to Plato.