In one sense, Polemarchus and Cephalus were not that far off the mark. However, in following the traditional notions, they were thinking about justice as a set of actions, rather than as a structure to society, a phenomenon that spreads out over a city as a whole.
In addition to the definition of justice, we also get the definitions of four other virtues in this section. The city’s courage, Socrates tells us, is located in the auxiliaries, because it is only their courage that will effect the city as a whole. Yet right after making this claim, he goes on to tell us that what the auxiliaries possess is not simply courage but something he calls “civic courage.” Many scholars have interpreted civic courage as a kind of second-rate courage. What the auxiliaries have, Socrates tells us, is the right beliefs about what is to be feared and what is not to be feared. Their courage is founded upon belief, rather than knowledge. Later in the book, he indicates that real virtue must be founded upon knowledge, suggesting that virtue based on habit or belief and not knowledge will fail when the going gets very tough. Since only the guardians possess knowledge, only the guardians can be truly virtuous or courageous.
Now that Socrates has identified societal justice, he turns to look for individual justice. Justice in the individual, as in the city, involves the correct power relationship among parts, with each part occupying its appropriate role. In the individual, the “parts” are not classes of society; instead, they are aspects of the soul—or sources of desire.
In order to make the case that individual justice parallels political justice, Socrates must claim that there are precisely three parts of the soul. By cataloging the various human desires, he identifies a rational part of the soul that lusts after truth, a spirited part of the soul that lusts after honor, and an appetitive part of the soul that lusts after everything else, including food, drink, sex, and especially money. These three parts of the soul correspond to the three classes in the just city. The appetite, or money-loving part, is the aspect of the soul most prominent among the producing class; the spirit or honor-loving part is most prominent among the auxiliaries; and reason, or the knowledge-loving part, is dominant in the guardians.
Just relations between the three parts of the soul mirror just relations among the classes of society. In a just person the rational part of the soul rules the other parts, with the spirited part acting as helper to keep the appetitive in line. Compare this to the city where the truth-loving guardians rule, with the honor-loving auxiliaries acting as their helpers to keep the money-loving producers in line. What it means for one part of the soul to “rule” the others is for the entire soul to pursue the desires of that part. In a soul ruled by spirit, for instance, the entire soul aims at achieving honor. In a soul ruled by appetite, the entire soul aims at fulfilling these appetites, whether these be for food, drink, sex, fine material goods, or hordes of wealth. In a just soul, the soul is geared entirely toward fulfilling whatever knowledge-loving desires reason produces.
Socrates has now completely fulfilled his first goal: he has identified justice on both the political and individual levels. Yet in giving an account of justice, he has deviated from our intuitive notions of what this virtue is. We tend to think of justice as a set of actions, yet Socrates claims that justice is really a result of the structure of the soul. After identifying individual justice, he demonstrates that a person who’s soul is in the right arrangement will behave according to the intuitive norms of justice. He needs to show that the notion of justice we have just arrived at is not counter to our intuitions—that this notion accounts for our intuitions and explains them. Socrates points out that since our just person is ruled by a love of truth, he will not be in the grips of lust, greed, or desire for honor. Because of this, Socrates claims, we can rest assured that he will never steal, betray friends or his city, commit adultery, disrespect his parents, violate an oath or agreement, neglect the gods, or commit any other acts commonly considered unjust. His strong love of truth weakens urges that might lead to vice.