But along the way he also presents arguments for his views on the nature of knowledge, on government, on the individual. This is as important as his thesis that the just man, even if he appears unjust, is better off than the unjust man (even if he appears just).
As far as the theory of knowledge is concerned, he distinguishes knowing something from mere opinion on the basis that one can only know something if one has a valid reason for it - a "justified true belief." He argues that there is somethign called "the Good" which is the sum of all truth and which cannot easily be known, but one must make the effort to understand. This is where he presents the allegory of the Cave. This is the story about the prisoners who are chained inside a cave facing the wall, so all they can see are shifting shadows from people moving around behind them. He then supposes someone breaks free and begins to exit to the cave. His eyesight would be poor at first in the light, but he would eventually be able to see the cause for the shadows, then see the outside world: the trees, the sky, the sun and stars, all of it. This would be Reality, not the shadows he and his fellow prisoners were accustomed to seeing. And so he would have a duty to return to the cave and attempt to tell his fellow prisoners what he had seen, even at risk of harm to his person and reputation.
This epistemological contribution is as significant as the ethical concerns that motivate Plato in composing the Republic: not jut the duty to do what one's taks is, ut the duty to seek out the truth and learn.
Plato wrote 'The Republic' in around 360BC. He wrote it in order to explore the notion of justice and specifically if the 'just' man can be happier than the 'unjust' man. It is a dialogue that goes to the heart of the true nature of philosophy and he does this by constructing an imaginary city that is ruled by philosopher kings.
The point that is essentially made is that justice is preferable to injustice, in that justice is the action of doing the right thing.A truly just society has the city-state mirroring the soul. (the soul has three parts and the three classes correspond to these areas - the guardians are wisdom, the auxilaries are courageous and the workers exhibit moderation).
Because of the human desire for power and the tendancy toward corruption that leads to tyranny, philosophic rule is advocated. The work explores government types and is a treatise on government.