Plato wrote the Republic in 380 BC. The first book of Plato's Republic is concerned with justice. What is justice, and why should one behave justly, are two questions which Socrates and his interlocutors attempt to answer. The first definition of justice is proposed by Cephalus. Cephalus is an old, wise, and very wealthy man.
He provides tremendous insight about old age. He says that as one grows older, the passions relax and one feels as if he has escaped from a mad and furious monster, and that one experiences a sense of calm and freedom. He also asserts that the greatest benefit his wealth has conferred upon him is that he never needed to intentionally or unintentionally deceive another man. For when a man nears the end of his life and considers his past transgressions, he begins to fear the potential punishments he will suffer in the afterlife. Cephalus concludes that justice is paying debts and telling the truth.
Socrates refutes Cephalus'definition of justice by positing several instances in which it is not just to tell the truth or to pay one's debts. For example, it is not just to return weapons entrusted to your care to a friend who is not in his right senses. Furthermore, if a friend who is not in his right senses approaches you and inquires where another man is so that he may kill him, then it is not just to tell him where that man is cephalus son polemarchus proposes the second definition he asserts that justice is doing good to friends and evil to enemies socrates refutes this definition by asserting that the just man never does evil even to his enemies socrates states that when something inflicts harm upon a horse the horse deteriorates in the excellence of a horse similarly when something injures a man the man deteriorates in the excellence of a man, which is justice. But a horseman by his art cannot injure a horse, nor can a musician by his art make men unmusical. Similarly, a just man by justice cannot make a man unjust.
Thus, Socrates concludes, only unjust men injure other men. To do evil is never just. Thrasymarchus provides the third definition. He states that justice is the interest of the stronger.
Thrasymachus elaborates that there are different types of governments, tyrannies, democracies, and aristocracies. Each government makes laws according to their own particular interests, and these laws are the justice which they deliver to their citizens. Anyone who breaks the laws is unjust.
Because the government has the power to make the laws, it is the stronger, and therefore justice is the interest of the stronger. Socrates refutes Thrasymachus by demonstrating that rulers are liable to err. and pass laws that are not in their best interest.
Some laws command citizens to behave contrary to the interests of the stronger. If justice is merely obeying the laws, then justice is not always the interest of the stronger. Thrasymarchus counters that when rulers pass laws contrary to their interest, then they are not the stronger at that point in time.
Thrasymarchus uses an analogy of a mathematician. When a mathematician makes a mistake while calculating, He is not a mathematician in so far as the name implies at that time. When he errs, his skill fails him, and he is not a mathematician.
Socrates proceeds to explain that every art has an interest. The art of medicine is concerned with the interests of the patient. The art of horsemanship is concerned with the interests of the horse. No art is concerned with its own interest, because it has none.
No physician, in so far as he is a physician, considers his own good in what he prescribes, but only the good of the patient. Thus, a ruler makes laws in the interest of the ruled, and not in the interest of himself. Each art gives us a particular good. Medicine gives us good health, navigation gives us safety on the seas, payment gives us money.
We do not confuse the goods of each art with one another. For example, the art of navigation is not confused with the art of medicine because one becomes healthy on a sea voyage. Furthermore, we do not confuse the art of making money with the art of medicine because one becomes healthy when he receives payment.
the artist never regards its own interest but only the interest of its subjects and thus men must be paid to rule because they pass laws in the interest of their subjects and not themselves society can pay rulers three different ways with money honor or by withholding a penalty for refusing to rule men who are not avaricious or ambitious are penalized if they do not rule because men less just than they will rule if they do not Thrasymachus declares that the unjust man is much happier than the just man, and that the just man is in fact miserable. Therefore, according to Thrasymachus, injustice is more advantageous than justice. Socrates proves that justice is wisdom and virtue, while injustice is ignorance and vice, by using an analogy of mathematicians. Just as a mathematician does not desire to go beyond a mathematician, but he does desire to be more knowledgeable in mathematics than someone who is not a mathematician, so too does the just man not desire more than the just, but does desire more than the unjust. Likewise, the man who is ignorant of mathematics desires more than the mathematician and the non-mathematicians, just as the unjust man desires more than both the just and unjust.
Finally, because justice is wisdom and virtue, it is stronger than injustice, which is ignorance. Socrates also notes that the unjust are incapable of common action. A group of thieves must behave justly towards one another if they wish to conspire.
If they are truly unjust, they would inflict evil upon one another and would not be able to work towards a common cause. Injustice is even more fatal in one individual. Injustice renders an individual incapable of any action because of the internal disorder. Finally, Socrates concludes that everything has an end and an excellence. The end of the eye is sight, the end of the ear is hearing, and the end of the soul is happiness.
If an eye's particular excellence deteriorates, then it will not be capable of achieving its particular end. Accordingly, if the soul's excellence, which is justice, deteriorates, then it will not be capable of attaining its end, which is happiness. Socrates concludes Book I by acknowledging that he has not adequately described the true nature of justice, but rather has only identified a few superficial attributes and consequences of behaving justly.