visit by Socrates to the Piraeus leads to a discussion at the house of Cephalus - a very old wealthy immigrant arms-manufacturer - on the subject of Justice: i.e how is the good man supposed to behave? The Greek word for "good" (agathos) implies "good at doing something". (A good pen is one that does its job. It writes. A good man is good at doing whatever it is that a man is supposed to do! )
hree popular definitions are brought up -
Justice is "paying one's debts" (Cephalus);
Justice is "helping friends and harming enemies" (Polemarchus - Cephalus' son); - the view, I'd suppose, of the Greek "man in the street."
Justice is "whatever is to the advantage of the stronger" (in other words whatever the strong person can get away with - he defines his own justice) - this is forcefully argued by the sophist Thrasymachus.
Socrates demolishes all the arguments - but Glaucon (one of Plato's brothers who was present at this fictitious discussion) doesn't believe that Thasymachus's argument has really been refuted: what is the point in being good?