Plato (427-347 BC) was born into a prominent Athenian family and was very close to his teacher Socrates who was democratically condemned to death -this can partly explain Plato's anger against this form of government. In the Republic he describes his ideal human society ruled by philosophers. I will focus firstly on his conception of a well-ruled state then on the existence of a ruling skill and finally on the philosophers' virtues that make them the most able to rule.
First and foremost, it is essential to describe the class system structuring Plato's city-state. According to their natural aptitudes the members of the community would be distributed into three classes, each of them with a specific social role. The artisans, or producers, at the basis of the social pyramid would provide the polis its economic needs, the auxiliaries would act as 'a combined military, executive, and police force' (Hobbs 2003: 405), and the philosopher-kings -the elite of the auxiliary class- would effectively rule the city.
The fact that Plato takes for granted that "it is impossible for one person to work properly at more than one area of expertise" (374a), although far from being indisputable, is the cornerstone of such a classification and, therefore, of his whole community.
Another key point is that, for Plato, a well ruled state is a just state. He conceives justice as 'minding your own business' -each class, and within it each individual, doing what he/she is naturally made for. The just polis could thus be compared to a body depending on the functioning of its organs so as to run properly (Roberts & Sutch 2004: 33).
Consequently, a just state will naturally tend to flourish aiming the good of the whole -which is linked, for Plato, to four cardinal values: wisdom, courage, temperance or...