Why do men behave justly? Is it because they fear societal punishment? Are they trembling before notions of divine retribution? Do the stronger elements of society scare the weak into submission in the name of law? Or do men behave justly because it is good for them to do so? Is justice, regardless of its rewards and punishments, a good thing in and of itself? How do we define justice? Plato sets out to answer these questions in The Republic. He wants to define justice, and to define it in such a way as to show that justice is worthwhile in and of itself. He meets these two challenges with a single solution: a definition of justice that appeals to human psychology, rather than to perceived behavior.