Answer to First Question

This is a continuation of this post.

1) Why begin with Cephalus, Polemarchus and Thrasymachus?

Justice is a topic that most people think they understand. Most people would recoil at the suggestion that justice (or righteousness) requires definition. Rarely does one find a need to define justice to know how to live from day to day. One knows it is not just to steal, or injure one's friend, or lie. The elderly Cephalus believes he has lived his life justly so why should he define justice? The young Polemarchus does not feel any strong motivation to carefully analyze the meaning of justice and he is satisfied by quoting the beautiful though shallow saying of Simonides. The sophist Thrasymachus is motivated only to win the argument not to find the truth. Socrates demonstrates that each of these interlocutors' opinions do not stand up once forced to contend with real cases. Should one return something to a friend when it might cause him harm? Should one harm one's enemies even though it is wrong to harm anyone? Does might truly make right? What these three individuals have in common is that they believe they know what justice is. They need Socrates to demonstrate to them (and to us, as the readers) that they indeed do not know. By beginning The Republic with the arguments of these three individuals Plato demonstrates the need to carefully examine justice and also enables the reader to come to the realization that he himself does not know what justice is.