In book 10, Socrates advocates for banishing poets from the city-state. He justifies this move by asserting that poets are dangerous. While people think poets are knowledgeable and wise, poets actually know nothing and write in images, which are distortions of reality. They also focus on the most irrational emotions in humans, as these are exciting, rather than the calm emotions of the rational, philosophical mind.

Because poets write about the most excessive and worst emotions, they encourage people to dwell on them, empathize with them, and even imitate them, which will not help build the just state. Socrates is not happy about banishing poets, but doesn't see an alternative.

Socrates then proceeds to show that the soul is immortal by stating that even the souls of the worst people are not destroyed by the terrible things they do. This means that the soul is immortal or indestructible.

Finally, Socrates relates the myth of Er, who is sent to heaven to report back on what goes on there. He states that the just people, the philosophers, know what kind of new life to choose after they die so that they will not go to hell. Thus they prosper, proving that the just prosper more generally.