Book X of the Republic includes Socrates' discussion of what kinds of poetry to allow into the callipolis. First, Socrates objects to imitative poetry on metaphysical grounds. Next, he voices concerns about the ability of poetry to stir up the emotions, potentially feeding appetites which could overpower the rational portion of the soul. However, Socrates ends by telling Glaucon a myth, implying that storytelling can contribute to ethical education.
Initially, Socrates reminds Glaucon that they had agreed to keep imitative poetry out of the callipolis. Now that Socrates has explained his metaphysical views with the segmented line and the allegory of the cave, he is able to raise a metaphysical objection to imitative art. He says that imitative art is three times removed from the truth because it an imitation of a real thing, which is itself less real than the form of the real thing. Hence Socrates is able to say that imitative arts lead away from higher reality and away from the truth.
Next, Socrates argues that poetic imitation stirs the appetites, enabling them to overcome reason. He says, "And in the case of sex, anger, and all the desires, pleasures, and pains that we say accompany all our actions, poetic imitation has the very same effect on us. It nurtures and waters them and establishes them as rulers in us when they ought to wither and be ruled" (Grube, 277). However, Socrates qualifies his objection by saying that if poetry can bring forward any argument showing that it belongs in a well-governed city, he would gladly admit it into the callipolis.
Finally, Socrates concludes by telling the myth of Er to Glaucon. This use of mythology may provide the very argument which Socrates seeks from poetry. He uses the myth in a final attempt to persuade Glaucon that the just life is better in itself than the unjust life. This use of mythology for ethical teaching presupposes that poetry can lead listeners to moral truth. Furthermore, Socrates had previously argued that they should employ an invented myth, the noble lie, to maintain order in the callipolis. These two examples suggest that poetry can contribute to the good life.