In Book I of The Republic, Thrasymachus sets up a challenge to justice. Thrasymachus is a Sophist, one of the teachers-for-hire who preached a creed of subjective morality to the wealthy sons of Athens. The Sophists did not believe in objective truth, including objective moral truth. They did not think, in other words, that anything was absolutely “right” or “wrong”; instead they viewed all actions as either advantageous or disadvantageous to the person performing them. If an action was advantageous then they thought you should engage in it, and if it was disadvantageous then they thought that you should refrain. Taking this belief to its logical conclusion, some of them went so far as to claim that law and morality are nothing but mere convention, and that one ought to try to get away with injustice and illegality whenever such action would be to one’s advantage. Plato meant to combat this attitude in The Republic.
Thrasymachus introduces the Sophist challenge by remarking that justice is nothing but the advantage of the stronger. He does not mean to define justice with this statement, but to debunk it. His claim proceeds from the basic Sophistic moral notion: that the norms considered just are nothing more than conventions which hamper those who adhere to them, and benefit those who flout them. Those who behave unjustly naturally gain power and become the rulers, the strong people in society. Justice is the advantage of the stronger because when stupid, weak people behave in accordance with justice, they are disadvantaged, and the strong (those who behave unjustly) are advantaged.
An alternate reading of Thrasymachus’s bold statement makes his claim seem slightly more subtle. According to this reading (put forward by C.D.C. Reeve), Thrasymachus is not merely making the usual assertion that the norms of justice are conventions; he claims further that these mores and norms are conventions that were put in place by the rulers (the “stronger”) for the purpose of promoting their own interests. Conceptions of justice, in this reading, are the products of propaganda and tools of oppressors.
Regardless of the interpretation we give to Thrasymachus’ 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. His attempt to meet this challenge occupies the rest of The Republic.
Before he can prove that justice is a good thing, Plato must first state what justice is. Instead of defining justice as a set of behavioral norms (as the traditional Greek thinkers did) Plato identifies justice as structural: political justice resides in the structure of the city; individual justice resides in the structure of the soul. The just structure of the city is summed up by the principle of specialization: each member of society must play the role for which his nature best suits him and not meddle in any other business. A man whose nature suits him to farming must farm and do nothing else; a man whose nature best suits him to building objects out of wood must be a carpenter and not bother with any other sort of work. Plato believes that this is the only way to ensure that each job is done as well as possible.
The principle of specialization keeps the farmer from carpentering, and the carpenter from farming. More important, it keeps both the farmer and the carpenter from becoming warriors and rulers. The principle of specialization separates society into three classes: the class of producers (including farmers, craftsmen, doctors, etc.), the class of warriors, and the class of rulers. Specialization ensures that these classes remain in a fixed relations of power and influence. Rulers control the city, establishing its laws and objectives. Warriors carry out the commands of rulers. Producers stay out of political affairs, only worrying themselves about the business of ruling insofar as they need to obey what the rulers say and the warriors enforce. A city set up in this way, Plato contends, is a just city.
Just as political justice consists in the structural relations among classes of society, Plato believes, individual justice consists in correct structural relations among parts of the soul. Paralleling the producers, warriors, and rulers in the city, Plato claims that each individual soul has three separate seats of desire and motivation: the appetitive part of our soul lusts after food, drink, sex, and so on (and after money most of all, since money is the means of satisfying the rest of these desires); the spirited part of the soul yearns for honor; the rational part of the soul desires truth and knowledge. In a just soul, these three parts stand in the correct power relations. The rational part must rule, the spirited part must enforce the rational part’s convictions, and the appetitive part must obey.
In the just soul, the desires of the rational, truth-loving part dictate the overall aims of the human being. All appetites and considerations of honor are put at the disposal of truth-loving goals. The just soul strives wholly toward truth. Plato identifies the philosopher (literally “truth lover”) as the most just individual, and sets him up as ruler of the just city.
Explaining his idea of a philosopher-king, Plato appeals to three successive analogies to spell out the metaphysical and epistemological theories that account for the philosopher’s irreplaceable role in politics. The analogy of the sun illuminates the notion of the Form of the Good, the philosopher-king’s ultimate object of desire. The line illustrates the four different grades of cognitive activity of which a human being is capable, the highest of which only the philosopher-kings ever reach. The allegory of the cave demonstrates the effects of education on the human soul, demonstrating how we move from one grade of cognitive activity to the next.
In the allegory of the cave, Plato asks us to imagine the following scenario: A group of people have lived in a deep cave since birth, never seeing any daylight at all. These people are bound in such a way that they cannot look to either side or behind them, but only straight ahead. Behind them is a fire, and behind the fire is a partial wall. On top of the wall are various statues, which are manipulated by another group of people, laying out of sight. Because of the fire, the statues cast shadows on the wall that the prisoners are facing. The prisoners watch the stories that these shadows play out, and because this is all they can ever see, they believe that these shadows are the most real things in the world. When they talk to one another about “men,” “women,” “trees,” “horses,” and so on, they refer only to these shadows.
Now he asks us to imagine that one of these prisoners is freed from his bonds, and is able to look at the fire and at the statues themselves. After initial pain and disbelief, he eventually realizes that all these things are more real than the shadows he has always believed to be the most real things; he grasps how the fire and the statues together caused the shadows, which are copies of the real things. He now takes the statues and fire as the most real things in the world.
Next this prisoner is dragged out of the cave into the world above. At first, he is so dazzled by the light in the open that he can only look at shadows, then he is able to look at reflections, then finally at the real objects—real trees, flowers, houses, and other physical objects. He sees that these are even more real than the statues were, and that those objects were only copies of these.
Finally, when the prisoner’s eyes have fully adjusted to the brightness, he lifts his sights toward the heavens and looks at the sun. He understands that the sun is the cause of everything he sees around him—of the light, of his capacity for sight, of the existence of flowers, trees, and all other objects.
The stages the prisoner passes through in the allegory of the cave correspond to the various levels on the line. The line, first of all, is broken into two equal halves: the visible realm (which we can grasp with our senses) and the intelligible realm (which we can only grasp with the mind). When the prisoner is in the cave he is in the visible realm. When he ascends into the daylight, he enters the intelligible.
The lowest rung on the cognitive line is imagination. In the cave, this is represented as the prisoner whose feet and head are bound, so that he can only see shadows. What he takes to be the most real things are not real at all; they are shadows, mere images. These shadows are meant to represent images from art. A man who is stuck in the imagination stage of development takes his truths from epic poetry and theater, or other fictions. He derives his conception of himself and his world from these art forms rather than from looking at the real world.
When the prisoner frees himself and looks at the statues he reaches the next stage in the line: belief. The statues are meant to correspond to the real objects of our sensation—real people, trees, flowers, and so on. The man in the cognitive stage of belief mistakenly takes these sensible particulars as the most real things.
When he ascends into the world above, though, he sees that there is something even more real: the Forms, of which the sensible particulars are imperfect copies. He is now at the stage of thought in his cognition. He can reason about Forms, but not in a purely abstract way. He uses images and unproven assumptions as crutches.
Finally, he turns his sights to the sun, which represents the ultimate Form, the Form of the Good. The Form of the Good is the cause of all other Forms, and is the source of all goodness, truth, and beauty in the world. It is the ultimate object of knowledge. Once the prisoner has grasped the Form of the Good, he has reached the highest stage of cognition: understanding. He no longer has any need for images or unproven assumptions to aid in his reasoning. By reaching the Form of the Good, he hits on the first principle of philosophy which explains everything without the need of any assumptions or images. He can now use this understanding derived from comprehending the Form of the Good to transform all his previous thought into understanding—he can understand all of the Forms. Only the philosopher can reach this stage, and that is why only he is fit to rule.
Plato is unable to provide direct detail about the Form of the Good, and instead illustrates his idea by comparing it to the sun. The Form of the Good is to the intelligible realm, he claims, as the sun is the visible realm. (In the metaphor, the fire in the cave represents the sun.) First of all, just as the sun provides light and visibility in the visible realm, the Form of the Good is the source of intelligibility. The sun makes sight possible, and, similarly, the Form of the Good is responsible for our capacity for knowledge. The sun causes things to come to be in the visible world; it regulates the seasons, makes flowers bloom, influences animals to give birth and so on. The Form of the Good is responsible for the existence of Forms, for their coming to be in the intelligible world.
One of Plato’s objectives in The Republic was to show that justice is worthwhile—that just action is a good in itself, and that one ought to engage in just activity even when it doesn’t seem to confer immediate advantage. Once he has completed his portrait of the most just man—the philosopher-king—he is in a position to fulfill this aim. In Book IX, Plato presents three arguments for the claim that it pays to be just. First, by sketching a psychological portrait of the tyrant, he attempts to prove that injustice takes such a wretched toll on a man’s psyche that it could not possibly be worth it (whereas a just soul is untroubled and calm). Next, he argues that, though each of the three main character types (money-loving, honor-loving, and truth-loving) have their own conceptions of pleasure and of the corresponding good life (each choosing his own life as the most pleasant sort), only the philosopher is in the position to judge since only he is capable of experiencing all three types of pleasure. Finally, he tries to demonstrate that only philosophical pleasure is really pleasure at all; all other pleasure is only cessation from pain.
In all likelihood, Plato did not consider any of these to be the primary source of justice’s worth. Plato’s goal was to prove that justice is worthwhile independent of the advantages it confers, so for him to argue that the worth of justice lies in the enormous pleasure it produces is beside his point. To say that we should be just because it will make our life more pleasant, after all, is just to say that we should be just because it is to our advantage to do so. Instead, we should expect to find him arguing that the worth of justice lies in some other source, preferably having something to do with objective goodness. This is why many philosophers, from Plato’s student Aristotle down to modern scholar Richard Kraut, believe that Plato’s real argument for the worth of justice takes place long before Book IX. They think, plausibly, that Plato locates the worth of justice in justice’s connection to the Forms, which he holds to be the most good things in the world. Justice is worthwhile, on this interpretation, not because of any advantage it confers, but because it involves grasping the Form of the Good and imitating it. The just man tries to imitate the Forms by making his own soul as orderly and harmonious as the Forms themselves.