Answer:

Plato’s Republic centers on a simple question: is it always better to be just than unjust? The puzzles in Book One prepare for this question, and Glaucon and Adeimantus make it explicit at the beginning of Book Two. To answer the question, Socrates takes a long way around, sketching an account of a good city on the grounds that a good city would be just and that defining justice as a virtue of a city would help to define justice as a virtue of a human being. Socrates is finally close to answering the question after he characterizes justice as a personal virtue at the end of Book Four, but he is interrupted and challenged to defend some of the more controversial features of the good city he has sketched. In Books Five through Seven, he addresses this challenge, arguing (in effect) that the just city and the just human being as he has sketched them are in fact good and are in principle possible. After this long digression, Socrates in Books Eight and Nine finally delivers three “proofs” that it is always better to be just than unjust. Then, because Socrates wants not only to show that it is always better to be just but also to convince Glaucon and Adeimantus of this point, and because Socrates’ proofs are opposed by the teachings of poets, he bolsters his case in Book Ten by indicting the poets’ claims to represent the truth and by offering a new myth that is consonant with his proofs.