The Republic

The Republic is a book by Plato. It was finished in 375 BC.Brickhouse, Thomas and Smith, Nicholas D. Plato (c. 427–347 BC), The Internet Encyclopedia of Philosophy, University of Tennessee, cf. Dating Plato's Dialogues. 
It asks the question 'why should people do good things?' and also the question 'are people punished for doing bad things?'. 
Plato said that people should not do bad things because people who do bad things end up unhappy.
However, people who do good things end up happy.

He also said that if people who do bad things get power in a society then that society will become an unhappy one.
Plato believed that philosophers are best able to do good things and so they should be given power in a society. 
He thought that non-philosophers should allow themselves to be ruled by philosophers and that if they do this then they will be happy, because the rule of peoples (democracy) often fall because of unreasonable confusion.
However, in order not to be tempted to do bad things, the philosophers who have power must not be able to have things or feel love.

Plato also talked about many other things while discussing these questions including metaphysics, psychology, religion and most branches of philosophy.
He introduced the philosophy called Platonism.

 Plato's argument (Less Simple) 
Plato thought that people and societies are very much alike.

Plato thought that people are made of three things:
 A mind that thinks and reasons
 A spirit or a self that looks after the person
 A body that does things, likes things, hates things and wants things (such as food, drink and sex).
He said that a good person will listen to all these things, but will let the mind control the other two.

Somebody who does not listen to all three parts, or who does not let the mind control the other two will be unhappy.
They might go mad because they do not let the mind control them.
Or they might do things that they later regret.
They will also be disliked by other people and will suffer because of that.
He said that they will be like a country in anarchy.

Plato also thought society should be made up of three things (types of people)
 Philosophers who think for the society
 Soldiers who look after the society
 Workers who do things in the society, who make food, drink and more workers.
He said that society needs all three things (types of people) but that only the philosophers will be good people.
The others will be dominated by their souls or bodies, not their minds.
The soldiers will not even listen to their minds, and the workers will not listen to their minds or their souls.
This is why the philosophers should rule and the other types of people should be soldiers and workers.

 References 

Category:Works by Plato