Cephalus states that he agrees with Sophacles that old age has allowed him to be free of the mad masters of appetitive desires. Moreover, wealth helps us be just – not to deceive others or cheat them.
Socrates is not happy with Cephalus’ description of justice as paying one’s debts and telling the truth. Would we want to give back weapons we’ve borrowed to a now insane friend?
Polemarchus takes over: it is just to give to each what is owed to him. This is more general: friends owe it to their friends to do good for them, never harm.
Yet Socrates whittles this down to absurdity: justice becomes a craft of stealing to benefit friends and harm enemies. Moreover, sometimes we fall in with a bad crowd. So we end up benefitting bad people at the expense of good people. As such, if we are to be just we end up having to benefit our enemies at the expense of our friends – contradicting Polemarchus' point.
Furthermore, it is not the function of a just person to harm a friend or anyone else.
Thrasymachus then states: justice is the advantage of the stronger, the advantage of the established rule. More importantly though, the subjects believe that the ruler never makes errors and decrees what is best for himself.
Socrates tries to argue that, just as a captain does what is best for his sailors, a ruler does what is best for their subjects. But Thrasymachus compares rulers to shepherds – looking after their sheep, but for an ulterior selfish purpose. Thrasymachus goes on to say again that while justice is what is advantageous to the stronger, injustice is to one’s own profit and advantage. Socrates struggles with this point.
If the strong rule in any given city and socialize their subjects with values that best serve the rulers, then even if the subjects see their ethical views as serving their own best interest, this is only because they are unaware of the influence the rulers have had on them.
This potentially undermines Socrates’ method of elenchus. If elenchus aims to draw upon the interlocutors beliefs to reach truth, the reliability of these beliefs is faulty if they are the product of their ruler's influence. This suggests we cannot discover what virtues are, only what people think they are as a result of being victims of a false ideology.
Thus, Socrates’ challenge is to show justice is in everyone’s best interests because it is required for true happiness, and to do this without presupposing that people’s beliefs about the virtues (or about happiness, for that matter) are true.