Key Lessons from Plato’s Republic — Book I

Advancing Justice

4 min readNov 12, 2020

Why do men behave righteously? Is that that they risk retribution from society? Are the notions of divine vengeance trembling before them? Do the Stronger forces of culture, in the name of the law, threaten the poor into submission? Or are men acting because it’s nice for them to do so? Is Justice a decent thing in and of itself, because of its rewards and punishments? How can Justice be defined? These are the questions that we’re going to be answering over the course of covering The Republic by Plato.


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.

Justice as Defined by The Many

Cephalus serves as the Greek tradition’s representative. His conception of justice is an attempt to express the fundamental principle of Hesiodic: that justice means living up to and being truthful with your legal obligations. This formulation is defeated by Socrates with a counterexample: returning a weapon to a madman. In a way, whether it belongs to him lawfully, you owe the madman his weapon, and yet this would be an unjust act, as 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. The underlying imperative is of rendering to each what is due and of giving to each what is appropriate.

Socrates points out that our judgment concerning friends and enemies is fallible and that we are not always friends with the most virtuous individuals, nor are our enemies always the scum of society.

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.

The nefarious outcome of this misunderstanding is revealed to us by Thrasymachus: the Sophist’s campaign to do away with justice, and all moral values, fully. Breaking violently through the argument, Thrasymachus announces that he has a greater description of justice to give. Justice, he claims, is nothing but the benefit of the more dominant. Although this is his definition, Thrasymachus suggests, it is not necessarily intended as a definition of justice as much as it is a delegitimization of justice.

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.

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.

  1. Socrates concludes 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.
  2. 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.

Conclusion of Book 1

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.

Setting the Stage for The Republic

For as long as there has been ethical thought, there have been immoralists, people who think that it is better to look out for their own interests than to follow rules of right and wrong.

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.

Here, we see 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. The Republic is grounded in this idea of building a city on principles of reason.

The challenge to Socrates and for Us is the same: to 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.




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