Plato’s Republic (380 BC)
Summaries taken from sparknotes.com
Summary of the cave allegory from Book VII
Socrates describes a dark scene. A group of people have lived in a deep cave since birth, never seeing the light of day. These people are bound so that they cannot look to either side or behind them, but only straight ahead. Behind them is a fire, and behind the fire is a partial wall. On top of the wall are various statues, which are manipulated by another group of people, lying out of sight behind the partial wall. Because of the fire, the statues cast shadows across the wall that the prisoners are facing. The prisoners watch the stories that these shadows play out, and because these shadows are all they ever get to see, they believe them to be the most real things in the world. When they talk to one another about “men,” “women,” “trees,” or “horses,” they are referring to these shadows. These prisoners represent the lowest stage on the line—imagination.
A prisoner is freed from his bonds, and is forced to look at the fire and at the statues themselves. After an initial period of pain and confusion because of direct exposure of his eyes to the light of the fire, the prisoner realizes that what he sees now are things more real than the shadows he has always taken to be reality. He grasps how the fire and the statues together cause the shadows, which are copies of these more real things. He accepts the statues and fire as the most real things in the world. This stage in the cave represents belief. He has made contact with real things—the statues—but he is not aware that there are things of greater reality—a world beyond his cave.
Next, this prisoner is dragged out of the cave into the world above. At first, he is so dazzled by the light up there that he can only look at shadows, then at reflections, then finally at the real objects—real trees, flowers, houses and so on. He sees that these are even more real than the statues were, and that those were only copies of these. He has now reached the cognitive stage of thought. He has caught his first glimpse of the most real things, the Forms.
When the prisoner’s eyes have fully adjusted to the brightness, he lifts his sight toward the heavens and looks at the sun. He understands that the sun is the cause of everything he sees around him—the light, his capacity for sight, the existence of flowers, trees, and other objects. The sun represents the Form of the Good, and the former prisoner has reached the stage of understanding.
The goal of education is to drag every man as far out of the cave as possible. Education should not aim at putting knowledge into the soul, but at turning the soul toward right desires. Continuing the analogy between mind and sight, Socrates explains that the vision of a clever, wicked man might be just as sharp as that of a philosopher. The problem lies in what he turns his sharp vision toward.
The overarching goal of the city is to educate those with the right natures, so that they can turn their minds sharply toward the Form of the Good. Once they have done this, they cannot remain contemplating the Form of the Good forever. They must return periodically into the cave and rule there. They need periodically to turn away from the Forms to return to the shadows to help other prisoners.
Summary of Book X
Socrates has now completed the main argument of The Republic; he has defined justice and shown it to be worthwhile. He turns back to the postponed question concerning poetry about human beings. In a surprising move, he banishes poets from the city. He has three reasons for regarding the poets as unwholesome and dangerous. First, they pretend to know all sorts of things, but they really know nothing at all. It is widely considered that they have knowledge of all that they write about, but, in fact, they do not. The things they deal with cannot be known: they are images, far removed from what is most real. By presenting scenes so far removed from the truth poets, pervert souls, turning them away from the most real toward the least.
Worse, the images the poets portray do not imitate the good part of the soul. The rational part of the soul is quiet, stable, and not easy to imitate or understand. Poets imitate the worst parts—the inclinations that make characters easily excitable and colorful. Poetry naturally appeals to the worst parts of souls and arouses, nourishes, and strengthens this base elements while diverting energy from the rational part.
Poetry corrupts even the best souls. It deceives us into sympathizing with those who grieve excessively, who lust inappropriately, who laugh at base things. It even goads us into feeling these base emotions vicariously. We think there is no shame in indulging these emotions because we are indulging them with respect to a fictional character and not with respect to our own lives. But the enjoyment we feel in indulging these emotions in other lives is transferred to our own life. Once these parts of ourselves have been nourished and strengthened in this way, they flourish in us when we are dealing with our own lives. Suddenly we have become the grotesque sorts of people we saw on stage or heard about in epic poetry.
Despite the clear dangers of poetry, Socrates regrets having to banish the poets. He feels the aesthetic sacrifice acutely, and says that he would be happy to allow them back into the city if anyone could present an argument in their defense.
Socrates then outlines a brief proof for the immortality of the soul. Basically, the proof is this: X can only be destroyed by what is bad for X. What is bad for the soul is injustice and other vices. But injustice and other vices obviously do not destroy the soul or tyrants and other such people would not be able to survive for long. So nothing can destroy the soul, and the soul is immortal.
Once Socrates has presented this proof, he is able to lay out his final argument in favor of justice. This argument, based on the myth of Er, appeals to the rewards which the just will receive in the afterlife. According to the myth, a warrior named Er is killed in battle, but does not really die. He is sent to heaven, and made to watch all that happens there so that he can return to earth and report what he saw. He observes an eschatalogical system which rewards virtue, particularly wisdom. For 1000 years, people are either rewarded in heaven or punished in hell for the sins or good deeds of their life. They are then brought together in a common area and made to choose their next life, either animal or human. The life that they choose will determine whether they are rewarded or punished in the next cycle. Only those who were philosophical while alive, including Odysseus who chooses to be reborn as a swan, catch on to the trick of how to choose just lives. Everyone else hurtles between happiness and misery with every cycle.
 The Republic is a fictional dialogue in which Socrates represents Plato’s thoughts.