In general, the first two books of Plato’s Republic are a discussion about the definition of justice. It doesn’t seem like a clear answer is arrived at, but through discussion, Plato examines whether it is simply always doing what’s right – repaying debts, etc. Another suggestion is that it is giving people what they deserve – good deeds to good people and evil deeds to evil people. They talk about why someone would want to be just, and whether injustice might be more beneficial, if you can avoid being caught, because it allows you to lie, steal, and cheat to get more than your share.
Book I begins with Socrates’ getting into a conversation with an old man named Cephalus. They discuss aging and decide that the difficulties and unhappiness of old age can be countered in part with wealth, but more important is having a good nature.
From there, Socrates begins a discussion about the definition of justice that goes throughout this book and next. The first argument is given by Cephalus’ son, Polemarchus. Polemarchus suggests that justice is about doing the right thing both in word and deed. However, Socrates’ finds a loophole – while this definition would suggest it is always just to repay a debt, you can imagine a situation in which your friend lent you a weapon, and then came to get it back to you when he was angry or acting crazy – it would be wrong to give your friend back the weapon, even though by not giving it back, you aren’t repaying the debt.
After that Polemarchus tries another tact – that justice may mean giving people what they deserve – i.e. doing good to good people and bad to bad people. However, Socrates points out that a just or good person can’t do bad things, so if a good person tried to carry out justice by doing something bad to a bad person, then the good person would no longer be good.
Then another person, Thrasymachus, enters the conversation and argues that the definition of justice is whatever is in the interest of the stronger. This means that the government or those in powers make laws in their own interests and the subjects have to do it. If subjects break the law, it is unjust. Socrates disagrees, saying that if the leader accidently gave an order that would result in his own harm, then the subjects are being commanded to do the leader injury, not do what’s in his interest. Also, he says that rulers actually do what’s in the interest of his subjects, not himself.
Thrasymachus continues that, in any case, injustice is more beneficial than justice. Injustice allows you to cheat and steal and get more wealth, pleasure, and power. In this way justice is the loser to injustice. Socrates disagrees, saying that the unjust can’t work together for common purposes, and it fragments the soul of the person. He argues that justice gives you a just soul and helps you live well and acquire knowledge. He says justice is the excellence of the soul and injustice the defect of the soul.
Now the same discussion is continued, but Glaucon carries on Thrasymachus’ argument. He says that people who are unjust but have a reputation for justice seem like they’d be the best off, because they get the spoils of injustice without anyone disliking them. He argues that if a person could be invisible, they would definitely steal, cheat, and do other unjust things. He suggests that people like to do injustice, but they don’t like injustice to be done to them, and that this is the basis for laws. People make laws that restrict their own ability to cheat/steal, etc. because this also inhibits the ability of others to cheat, steal, and otherwise be unjust towards him. Law is really the only thing holding people back from doing bad things.
After this, Socrates begins talking about the government. He says that cities/governments are not a contract, but a natural occurance, based on the need of people to cooperate and trade with one another.