The final book of Plato’s Republic begins with Socrates returning to the question of banishing the poets that was first addressed in Book III. Book X is perhaps the most vexing and troubling book in the Republic.
Book X serves as a kind of epilogue, an afterward to the main text. The question of justice has been tacitly answered in the opening books, and it has now been sufficiently proven, at least to those present, that justice is preferable to injustice and that the kingly or aristocratic regime is best, along with the coupled soul, and that the kingly or aristocratic man is happiest. With Glaucon’s agreement the questions of the Republic have been answered.
However, Socrates returns to the question of the poets and their banishment. He reminds Glaucon of their lies and their lack of knowledge. They paint pictures of things they do not fully understand, and create wayward phantoms that may either help or hurt the regime. They are unregulated and invoke the spirited passions in men, the tragic pity and the comedy. Yet Socrates strikes a much more conciliatory tone at this late hour, just as the sun is presumably beginning to rise. He recalls the ancient quarrel that exists between poetry and philosophy (a la Aristophanes), but notes that if poetry can justify itself by reasons, as well as by meter and verse, then it may be allowed to re-enter the city. This crucial opening of the door for poetry preserves the integrity of philosophy lighted by the way of reason.
Socrates next provides a proof for the immortality of the soul, proceeding from commonly held beliefs. He and Glaucon come to the conclusion that bad things have the power to destroy, like rust on metal for example. Similarly, vice and injustice are bad for the soul. However, they do not destroy the soul, and therefore the soul is immortal.
Lastly, Socrates gives a defense of justice on behalf of the theologians and poets. He gives an unusual account, called the “Myth of Er”, myth meaning mythos, referring to an account or a story. In it, justice is defended on the grounds that individuals will reap the rewards and benefits after life. A summary of the Myth of Er is as follows: Er is a soldier killed in battle from Pamphylis (in modern day Turkey) and his body remains unusually well-preserved on the battle field for ten days. He is brought back and placed on the pyre. Meanwhile, Er is brought to the after-life with many other souls as companions. He comes upon two holes in and out of the heavens, and two holes in and out of the ground. Judges are seated in the middle directing people one way or another. The judges instruct Er to be vigilant as he will be asked to report this information to people upon his return. Wisdom and virtue are rewarded by the judges. People are sent on a 1,000 year journey paying for their actions in life, either in the bliss of the heavens or the tortures under the earth. Only those who choose the philosophic life while alive, like Orpheus, are rewarded. After seven days in this meadow, Er and the other souls travel for four more days until they see a bright rainbow light. After another day of traveling they arrive at the spindle of Necessity with the Sirens. The souls, except for Er, drew lots and each soul came forward one at a time to choose their next life. One chose a fateful life of a tyrant, and was to be punished to eat his own children. Some animals chose human lives, and visa versa. Then each was assigned a demon, or a kind of guardian spirit, and they passed beneath the throne of lady Necessity, across the plane of Oblivion, to the River Lethe (River of Forgetfulness). Each soul, except Er, drank and fell asleep and during the night they were transported while asleep to their new place of birth. Er awoke suddenly on his funeral pyre and recalled the whole story of life after death.
Socrates uses the Myth of Er to bolster the importance of acting justly, and also to further demonstrate the immortality of the soul. It should be noted that Socrates delivers this myth directly to Glaucon. Since Socrates speaks differently to different men, more fruitful inquiry of the Republic might pursue the lines of discussion he engages in with Adeimantus, the most important member of the dialogue whom Socrates engages with.