In the second half of Book II, Socrates is put on trial, reluctantly defending justice against the false accusations of the Athenian brothers, Glaucon and Adeimantus. He suggests they examine the question of justice in a larger way, not like men who are squinting at small letters from a distance. Socrates proposes that they watch a “city coming into being in speech” (369a) so that they may investigate the nature of justice on a larger scale, at the level of the city. This is distinct from a city coming into being in physis (or nature). That is, the city in speech is not the natural city.
At any rate, the city comes into being because each man is not self-sufficient but is in need of much. Each human being is erotic and humans share a common participation in eros with one another and as a result they are drawn to the city out of necessity. Recall the earlier claims of the two brothers. They are concerned with Aristotle’s “First Cause”, the Material Cause, for which Socrates lays out an explanation for the city. Because of the needs of men, they gather in settlements, and their primary need is for existing and living, but the second need is for housing and clothing and such. This first city, therefore, is the City of Utmost Necessity, composed of four or five men.
Soon, however, it is discovered that men would do a finer job if they focused on one art in particular -thus the division of labor is introduced. The city will also require more citizens for all its jobs. When asked where to find injustice or justice in this city, Adeimantus suggests it might perhaps be in the needs these men and women have for one another. He implies that justice has a kinship with eros. Socrates calls this the “True, or Healthy City” as it lives within its means and keeps an eye out against poverty or war.
Suddenly, Glaucon interrupts the conversation noting that none of the men in the city will have fine things and luxuries. This leads to the conversation of how The Luxurious City comes into being, or the Feverish City. It grows to include reclining couches and excesses, and thus the need for war is introduced. However, war presupposes friends and enemies of the city, and thus there is a need for warriors to protect the property and the luxuries of the city. This point leads to a conversation about the adequate training of the warriors, or guardians, who are primarily important for the city. They must be trained to love the city and hate the enemies, and not use their force against the city. They must be made to be virtuous. They must be trained like dogs, and this begins with an education in music and gymnastics. The music portion includes the stories that are told to children at a young and impressionable age. The false stories of the gods and the city will be highly regulated and many sections from Homer and Hesiod will be eliminated. The end, or final cause, of the education of the warriors is found to be eros of the beautiful. From their crop must be the caring, or love (philia) of the city. The remaining discussion of the education of the guardians continues in Book III.