Plato's masterpiece was the Republic. Here more than anywhere else every question is connected with every other question concerning the topics of knowledge and virtue. The method in the Republic is for Socrates to begin with a straightforward question such as, "What is justice?" He concluded that justice is a primarily a benefit for the one who possesses it.
For Socrates, the one who is "unjust" on the other hand is miserable.
So the structure of the concern has moved from "What is justice?" to "What is the benefit of justice?"
In further addressing the concern of justice, Socrates had to give a theory of human nature and the point that virtue is more than knowledge is stressed. Knowledge is to be in control of the non-rational senses.
Then Socrates moved to a discussion of a society in which knowledge is in control which evolves into a political theory which then progresses into a discussion of knowledge in the realm of the sciences, mathematics and ultimately the concern proceeded to the relationship of knowledge to the afterlife.
So the Republic is a profound work in that it stressed the unitary nature of each topic of concern.
