They wanted to arrive at the truth, first, about the nature of justice and injustice, and secondly, about their relative advantages.

I told them, what I really thought, that the enquiry would be of a serious nature, and would require very good eyes.

Seeing then, I said, that we are no great wits, I think that we had better adopt a method which I may illustrate thus; suppose that a short-sighted person had been asked by some one to read small letters from a distance; and it occurred to some one else that they might be found in another place which was larger and in which the letters were larger--if they were the same and he could read the larger letters first, and then proceed to the lesser--this would have been thought a rare piece of good fortune.
Very true, said Adeimantus; but how does the illustration apply to our enquiry?
I will tell you, I replied; justice, which is the subject of our enquiry, is, as you know, sometimes spoken of as the virtue of an individual, and sometimes as the virtue of a State.
True, he replied.
And is not a State larger than an individual?
It is.
Then in the larger the quantity of justice is likely to be larger and more easily discernible.

I propose therefore that we enquire into the nature of justice and injustice, first as they appear in the State, and secondly in the individual, proceeding from the greater to the lesser and comparing them.
That, he said, is an excellent proposal.
And if we imagine the State in process of creation, we shall see the justice and injustice of the State in process of creation also.
I dare say.
When the State is completed there may be a hope that the object of our search will be more easily discovered.
Yes, far more easily.
But ought we to attempt to construct one?
I said; for to do so, as I am inclined to think, will be a very serious task.

Reflect therefore.
I have reflected, said Adeimantus, and am anxious that you should proceed.
A State, I said, arises, as I conceive, out of the needs of mankind; no one is self-sufficing, but all of us have many wants.