Yes, replies Socrates, but the world will say, Cephalus, that you are happy in old age because you are rich.
'And there is something in what they say, Socrates, but not so much as they imagine--as Themistocles replied to the Seriphian, "Neither you, if you had been an Athenian, nor I, if I had been a Seriphian, would ever have been famous," I might in like manner reply to you, Neither a good poor man can be happy in age, nor yet a bad rich man.' Socrates remarks that Cephalus appears not to care about riches, a quality which he ascribes to his having inherited, not acquired them, and would like to know what he considers to be the chief advantage of them.

Cephalus answers that when you are old the belief in the world below grows upon you, and then to have done justice and never to have been compelled to do injustice through poverty, and never to have deceived anyone, are felt to be unspeakable blessings.

Socrates, who is evidently preparing for an argument, next asks, What is the meaning of the word justice?
To tell the truth and pay your debts?
No more than this?
Or must we admit exceptions?
Ought I, for example, to put back into the hands of my friend, who has gone mad, the sword which I borrowed of him when he was in his right mind?
'There must be exceptions.' 'And yet,' says Polemarchus, 'the definition which has been given has the authority of Simonides.' Here Cephalus retires to look after the sacrifices, and bequeaths, as Socrates facetiously remarks, the possession of the argument to his heir, Polemarchus...
The description of old age is finished, and Plato, as his manner is, has touched the key-note of the whole work in asking for the definition of justice, first suggesting the question which Glaucon afterwards pursues respecting external goods, and preparing for the concluding mythus of the world below in the slight allusion of Cephalus.

The portrait of the just man is a natural frontispiece or introduction to the long discourse which follows, and may perhaps imply that in all our perplexity about the nature of justice, there is no difficulty in discerning 'who is a just man.' The first explanation has been supported by a saying of Simonides; and now Socrates has a mind to show that the resolution of justice into two unconnected precepts, which have no common principle, fails to satisfy the demands of dialectic.
...He proceeds: What did Simonides mean by this saying of his?
Did he mean that I was to give back arms to a madman?
'No, not in that case, not if the parties are friends, and evil would result.

He meant that you were to do what was proper, good to friends and harm to enemies.' Every act does something to somebody; and following this analogy, Socrates asks, What is this due and proper thing which justice does, and to whom?
He is answered that justice does good to friends and harm to enemies.
But in what way good or harm?
'In making alliances with the one, and going to war with the other.' Then in time of peace what is the good of justice?
The answer is that justice is of use in contracts, and contracts are money partnerships.