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In The Republic, Plato, speaking through his teacher Socrates, sets out to answer two questions. What is justice? Why should we be just? Book I sets up these challenges. The interlocutors engage in a Socratic dialogue similar to that found in Plato’s earlier works. While among a group of both friends and enemies, Socrates poses the question, “What is justice?” He proceeds to refute every suggestion offered, showing how each harbors hidden contradictions. Yet he offers no definition of his own, and the discussion ends in aporia—a deadlock, where no further progress is possible and the interlocutors feel less sure of their beliefs than they had at the start of the conversation. In Plato’s early dialogues, aporia usually spells the end. The Republic moves beyond this deadlock. Nine more books follow, and Socrates develops a rich and complex theory of justice.

When Book I opens, Socrates is returning home from a religious festival with his young friend Glaucon, one of Plato’s brothers. On the road, the three travelers are waylaid by Adeimantus, another brother of Plato, and the young nobleman Polemarchus, who convinces them to take a detour to his house. There they join Polemarchus’s aging father Cephalus, and others. Socrates and the elderly man begin a discussion on the merits of old age. This discussion quickly turns to the subject of justice.

Cephalus, a rich, well-respected elder of the city, and host to the group, is the first to offer a definition of justice. Cephalus acts as spokesman for the Greek tradition. His definition of justice is an attempt to articulate the basic Hesiodic conception: that justice means living up to your legal obligations and being honest. Socrates defeats this formulation with a counterexample: returning a weapon to a madman. You owe the madman his weapon in some sense if it belongs to him legally, and yet this would be an unjust act, since it would jeopardize the lives of others. So it cannot be the case that justice is nothing more than honoring legal obligations and being honest.

At this point, Cephalus excuses himself to see to some sacrifices, and his son Polemarchus takes over the argument for him. He lays out a new definition of justice: justice means that you owe friends help, and you owe enemies harm. Though this definition may seem different from that suggested by Cephalus, they are closely related. They share the underlying imperative of rendering to each what is due and of giving to each what is appropriate. This imperative will also be the foundation of Socrates’s principle of justice in the later books. Like his father’s view, Polemarchus’s take on justice represents a popular strand of thought—the attitude of the ambitious young politician—whereas Cephalus’s definition represented the attitude of the established, old businessman.

Socrates reveals many inconsistencies in this view. He points out that, because our judgment concerning friends and enemies is fallible, this credo will lead us to harm the good and help the bad. We are not always friends with the most virtuous individuals, nor are our enemies always the scum of society. Socrates points out that there is some incoherence in the idea of harming people through justice.

All this serves as an introduction to Thrasymachus, the Sophist. We have seen, through Socrates’s cross-examination of Polemarchus and Cephalus, that the popular thinking on justice is unsatisfactory. Thrasymachus shows us the nefarious result of this confusion: the Sophist’s campaign to do away with justice, and all moral standards, entirely. Thrasymachus, breaking angrily into the discussion, declares that he has a better definition of justice to offer. Justice, he says, is nothing more than the advantage of the stronger. Though Thrasymachus claims that this is his definition, it is not really meant as a definition of justice as much as it is a delegitimization of justice. He is saying that it does not pay to be just. Just behavior works to the advantage of other people, not to the person who behaves justly. Thrasymachus assumes here that justice is the unnatural restraint on our natural desire to have more. Justice is a convention imposed on us, and it does not benefit us to adhere to it. The rational thing to do is ignore justice entirely.

The burden of the discussion has now shifted. At first, the only challenge was to define justice; now justice must be defined and proven to be worthwhile. Socrates has three arguments to employ against Thrasymachus’ claim. First, he makes Thrasymachus admit that the view he is advancing promotes injustice as a virtue. In this view, life is seen as a continual competition to get more (more money, more power, etc.), and whoever is most successful in the competition has the greatest virtue. Socrates then launches into a long and complex chain of reasoning which leads him to conclude that injustice cannot be a virtue because it is contrary to wisdom, which is a virtue. Injustice is contrary to wisdom because the wise man, the man who is skilled in some art, never seeks to beat out those who possess the same art. The mathematician, for instance, is not in competition with other mathematicians.

Socrates then moves on to a new argument. Understanding justice now as the adherence to certain rules which enable a group to act in common, Socrates points out that in order to reach any of the goals Thrasymachus earlier praised as desirable one needs to be at least moderately just in the sense of adhering to this set of rules.

Finally, he argues that since it was agreed that justice is a virtue of the soul, and virtue of the soul means health of the soul, justice is desirable because it means health of the soul.

Thus ends Book I. Socrates and his interlocutors are no closer to a consensus on the definition of justice, and Socrates has only advanced weak arguments in favor of justice’s worth. But the terms of our challenge are set. Popular, traditional thinking on justice is in shambles and we need to start fresh in order to defeat the creeping moral skepticism of the Sophists.


While The Republic is a book concerned with justice, it also addresses many other topics. Some scholars go so far as to say that the book is primarily about something other than justice. Critic Allan Bloom, for instance, reads the book first and foremost as a defense of philosophy—as Socrates’s second “apology.” Socrates was executed by the city of Athens for practicing philosophy. The leaders of Athens had decided that philosophy was dangerous and sought to expel it from their city. Socrates had called the old gods and the old laws into question. He challenged, and asked others to challenge, the fundamental beliefs upon which their society rested.

In The Republic, Bloom says, Plato is trying to defend the act for which his teacher was executed. His aim is to reveal why the philosopher is important, and what the philosopher’s relationship to the city should be. While a philosopher is potentially subversive to any existing regimes, according to Plato, he is crucial to the life of the just city. Plato wanted to show how philosophy can be vital to the city. Bloom calls The Republic the first work of political science because it invents a political philosophy grounded in the idea of building a city on principles of reason.

Read more about Plato's life and work.

Bloom’s interpretation follows from an understanding of Plato’s ideas about justice and just cities in The Republic, which is how the book demands to be read at first. Looking at The Republic as a work on justice, we first need to ask why justice has to be defended. As Thrasymachus makes clear, justice is not universally assumed to be beneficial. For as long as there has been ethical thought, there have been immoralists, people who think that it is better to look out for your own interest than to follow rules of right and wrong.

Traditionally, the Greek conception of justice came from poets like Hesiod, who in Works and Days presents justice as a certain set of acts that must be followed. The reason for being just, as presented by the traditional view, was consideration of reward and punishment: Zeus rewards those who are good and punishes those who are bad. In late fifth century Athens, this conception of divine reward and retribution had lost credibility. No one believed that the gods rewarded the just and punished the unjust. People could see that many unjust men flourished, and many of the just were left behind. In the sophisticated democracy that evolved in Athens, few were inclined to train their hopes on the afterlife. Justice became a matter of great controversy.

Leading the controversy were the Sophists, the general educators hired as tutors to the sons of the wealthy. The Sophists tended not to believe in objective truth, or objective standards of right and wrong. They regarded law and morality as conventions. The Sophist Antiphon, for example, openly declared that we ought to be unjust when being unjust is to our advantage.

Read more about Hesiod and the Sophists.

Plato felt that he had to defend justice against these onslaughts. The Sophistic challenge is represented in The Republic by Thrasymachus, who declares that justice is nothing but the advantage of the stronger. Since this statement motivates the entire defense that is to follow, it deserves analysis. What exactly does Thrasymachus mean by claiming that justice is the advantage of the stronger? Who are the stronger? What is their advantage?

On the first reading, Thrasymachus’s claim boils down to the basic Sophistic moral notion that the norms and mores we consider just are conventions that hamper those who adhere to them and benefit those who flout them. Those who behave unjustly naturally gain power and become rulers and strong people in society. When stupid, weak people behave in accordance with justice, they are disadvantaged, and the strong are at an advantage. An alternate reading of Thrasymachus’s bold statement makes his claim seem more subtle. On this reading, put forward by C.D.C. Reeve, Thrasymachus is not merely making the usual assertion that the norms and mores of justice are conventions; he is further claiming that these mores and norms are conventions put in place by rulers to promote their own interests and to keep their subjects in a state of oppression.

Read more about justice as the advantage of the stronger.

This second reading is interesting because it challenges not only our conception of right and wrong, but Socrates’s usual way of finding truth. Socrates’s method of elenchus proceeds by building up knowledge out of people’s true beliefs. If Thrasymachus is right, then we do not have any true beliefs about justice. All we have are beliefs forced on us by rulers. In order to discover the truth about right and wrong, we must abandon the old method and start from scratch: building up knowledge without resting on traditional beliefs. In the next book, Plato abandons the method of elenchus. and begins the discussion from scratch.

Regardless of how we interpret Thrasymachus’s statement, the challenge to Socrates is the same: he must prove that justice is something good and desirable, that it is more than convention, that it is connected to objective standards of morality, and that it is in our interest to adhere to it.

Read more about why it pays to be just.