Socrates believes he has adequately responded to Thrasymachus and is through with the discussion of justice, but the others are not satisfied with the conclusion they have reached. Glaucon, one of Socrates’ young companions, explains what they would like him to do. Glaucon states that all goods can be divided into three classes: things that we desire only for their consequences, such as physical training and medical treatment; things that we desire only for their own sake, such as joy; and, the highest class, things we desire both for their own sake and for what we get from them, such as knowledge, sight, and health. What Glaucon and the rest would like Socrates to prove is that justice is not only desirable, but that it belongs to the highest class of desirable things: those desired both for their own sake and their consequences.

Glaucon points out that most people class justice among the first group. They view justice as a necessary evil, which we allow ourselves to suffer in order to avoid the greater evil that would befall us if we did away with it. Justice stems from human weakness and vulnerability. Since we can all suffer from each other’s injustices, we make a social contract agreeing to be just to one another. We only suffer under the burden of justice because we know we would suffer worse without it. Justice is not something practiced for its own sake but something one engages in out of fear and weakness.

To emphasize his point, Glaucon appeals to a thought experiment. Invoking the legend of the ring of Gyges, he asks us to imagine that a just man is given a ring which makes him invisible. Once in possession of this ring, the man can act unjustly with no fear of reprisal. No one can deny, Glaucon claims, that even the most just man would behave unjustly if he had this ring. He would indulge all of his materialistic, power-hungry, and erotically lustful urges. This tale proves that people are only just because they are afraid of punishment for injustice. No one is just because justice is desirable in itself.

Glaucon ends his speech with an attempt to demonstrate that not only do people prefer to be unjust rather than just, but that it is rational for them to do so. The perfectly unjust life, he argues, is more pleasant than the perfectly just life. In making this claim, he draws two detailed portraits of the just and unjust man. The completely unjust man, who indulges all his urges, is honored and rewarded with wealth. The completely just man, on the other hand, is scorned and wretched.

His brother, Adeimantus, breaks in and bolsters Glaucon’s arguments by claiming that no one praises justice for its own sake, but only for the rewards it allows you to reap in both this life and the afterlife. He reiterates Glaucon’s request that Socrates show justice to be desirable in the absence of any external rewards: that justice is desirable for its own sake, like joy, health, and knowledge.

Coming on the heels of Thrasymachus’ attack on justice in Book I, the points that Glaucon and Adeimantus raise—the social contract theory of justice and the idea of justice as a currency that buys rewards in the afterlife—bolster the challenge faced by Socrates to prove justice’s worth. With several ideas of justice already discredited, why does Plato further complicate the problem before Socrates has the chance to outline his own ideas about justice?

The first reason is methodological: it is always best to make sure that the position you are attacking is the strongest one available to your opponent. Plato does not want the immoralist to be able to come back and say, “but justice is only a social contract” after he has carefully taken apart the claim that it is the advantage of the stronger. He wants to make sure that in defending justice, he dismantles all the best arguments of the immoralists.

The accumulation of further ideas about justice might be intended to demonstrate his new approach to philosophy. In the early dialogues, Socrates often argues with Sophists, but Thrasymachus is the last Sophist we ever see Socrates arguing with. From now on, we never see Socrates arguing with people who have profoundly wrong values. There is a departure from the techniques of elenchus and aporia, toward more constructive efforts at building up theory.

The Republic was written in a transitional phase in Plato’s own life. He had just founded the Academy, his school where those interested in learning could retreat from public life and immerse themselves in the study of philosophy. In his life, Plato was abandoning Socrates’ ideal of questioning every man in the street, and in his writing, he was abandoning the Sophist interlocuter and moving toward conversational partners who, like Glaucon and Adeimantus, are carefully chosen and prepared. In the dialogues, they are usually Socrates’ own students.

Plato had decided at this point that philosophy can only proceed if it becomes a cooperative and constructive endeavor. That is why in his own life he founded the Academy and his writings paired Socrates with partners of like mind, eager to learn. Glaucon and Adeimantus repeat the challenge because they are taking over the mantle as conversational partners. Discussion with the Sophist Thrasymachus can only lead to aporia. But conversation with Glaucon and Adeimantus has the potential to lead to positive conclusions.

This might seem like a betrayal of his teacher’s mission, but Plato probably had good reason for this radical shift. Confronting enemies has severe limits. If your viewpoint differs radically from that of your conversational partner, no real progress is possible. At most, you can undermine one another’s views, but you can never build up a positive theory together.

Socrates is reluctant to respond to the challenge that justice is desirable in and of itself, but the others compel him. He lays out his plan of attack. There are two kinds of justice political—the justice belonging to a city or state—and individual—the justice of a particular man. Since a city is bigger than a man, he will proceed upon the assumption that it is easier to first look for justice at the political level and later inquire as to whether there is any analogous virtue to be found in the individual. To locate political justice, he will build up a perfectly just city from scratch, and see where and when justice enters it. This project will occupy the Republic until Book IV.

Socrates introduces the foundational principle of human society: the principle of specialization. The principle of specialization states that each person must perform the role for which he is naturally best suited and that he must not meddle in any other business. The carpenter must only builds things, the farmer must only farm. Behind this principle is the notion that human beings have natural inclinations that should be fulfilled. Specialization demands not only the division of labor, but the most appropriate such division. Only in this way, Socrates is convinced, can everything be done at the highest level possible.

Having isolated the foundational principle of the city, Socrates is ready to begin building it. The first roles to fill are those that will provide for the necessities of life, such as food, clothing, health, and shelter. The just city is populated by craftsmen, farmers, and doctors who each do their own job and refrain from engaging in any other role. They are all members of what Socrates deems the “producing class,” because their role is to produce objects for use.

Socrates calls this city the “healthy city” because it is governed only by necessary desires. In the healthy city, there are only producers, and these producers only produce what is absolutely necessary for life. Glaucon looks less kindly on this city, calling it a “city of pigs.” He points out that such a city is impossible: people have unnecessary desires as well as these necessary ones. They yearn for rich food, luxurious surroundings, and art.

The next stage is to transform this city into the luxurious city, or the “city with a fever.” Once luxuries are in demand, positions like merchant, actor, poet, tutor, and beautician are created. All of this wealth will necessarily lead to wars, and so a class of warriors is needed to keep the peace within the city and to protect it from outside forces. The producers cannot act as our warriors because that would violate our principle of specialization.

Socrates spends the rest of this book, and most of the next, talking about the nature and education of these warriors, whom he calls “guardians.” It is crucial that guardians develop the right balance between gentleness and toughness. They must not be thugs, nor can they be wimpy and ineffective. Members of this class must be carefully selected—people with the correct nature or innate psychology. In particular, guardians should be spirited, or honor--loving, philosophical, or knowledge-loving, and physically strong and fast.

Nature is not sufficient to produce guardians. Nature must be protected and augmented with education. The education of guardians will involve physical training for the body, and music and poetry for the soul. Education of guardians is the most important aspect of the city. It is the process of purification through which the unhealthy, luxurious city can be purged and purified. Because the education of the guardians is so important, Socrates walks us through it in painstaking detail.

He begins by describing what sort of stories will be permitted in the city. The stories told to the young guardians-in-training, he warns, must be closely supervised, because it is chiefly stories that shape a child’s soul, just as the way parents handle an infant shapes his body. The remainder of Book II, therefore, is a discussion of permissible tales to tell about the gods. Socrates comes up with two laws to govern the telling of such stories. First, the gods must always be represented as wholly good and as responsible only for what is good in the world. If the gods are presented otherwise (as the warring, conniving, murderous characters that the traditional poetry depicts them to be), children will inevitably grow up believing that such behavior is permissible, even admirable. Second, the gods cannot be represented as sorcerers who change themselves into different forms or as liars. Otherwise, children will grow up without a proper reverence for truth and honesty.

The basic principle of education, in Plato’s conception, is that the soul, like the body, can have both a healthy and unhealthy state. As with the body, this state is determined by what the soul consumes and by what it does. Education determines what images and ideas the soul consumes and what activities the soul can and cannot engage in. Since the soul is always consuming, the stimuli available in the city must be rigidly controlled. Plato compares souls to sheep, constantly grazing. If you place sheep in a field of poisoned grass, and they consume this grass little by little, they will eventually sicken and die. Similarly, if you surround a soul with unwholesome influences, then gradually the soul will take these in and sicken. For this reason, Plato does not limit himself to dictating the specific coursework that will be given to the guardians, but also dictates what will be allowed into the cultural life of the city as a whole. The guardians, like all others, are constantly absorbing images. Practically speaking, there is little difference between the official school curriculum and the cultural life of the city in general.

Plato prescribes severe dictates concerning the cultural life of the city. He rules out all poetry, with the exception of hymns to the gods and eulogies for the famous, and places restraints on painting and architecture. Though Plato expresses regret at these aesthetic sacrifices, he feels they must be made for the sake of education, which transforms the unhealthy luxurious city into a pure and just city. How does it do this? The answer will not become clear until we understand what political justice is.

We might also ask at this point whether it is only the education of the guardians that is so important. If education determines whether a soul is sick or healthy, do we not care about the souls of the other members of society? The answer, probably, is that we do care about educating all souls, but since we are currently focusing on the good of the city, we are only interested in what will effect the city as a whole. Because of the way our city is set up, with the producing class excluded from political life, their education is not as important to the good of the city as the education of the guardians. Although education is important for everyone, the education of the producers, which would focus on development of skills approriate to specialized vocation, is not as relevant to the good of the city as a whole. When the discussion turns to questions of the individual, Socrates will identify one of the main goals of the city as the education of the entire populace as far as they can be educated.