Plato: The State and the Soul
Imagining their likely origins in the prehistorical past, Plato argued that societies are invariably formed for a particular purpose. Individual human beings are not self-sufficient; no one working alone can acquire all of the genuine necessities of life. In order to resolve this difficulty, we gather together into communities for the mutual achievement of our common goals. This succeeds because we can work more efficiently if each of us specializes in the practice of a specific craft: I make all of the shoes; you grow all of the vegetables; she does all of the carpentry; etc. Thus, Plato held that separation of functions and specialization of labor are the keys to the establishment of a worthwhile society.
The result of this original impulse is a society composed of many individuals, organized into distinct classes (clothiers, farmers, builders, etc.) according to the value of their role in providing some component part of the common good. But the smooth operation of the whole society will require some additional services that become necessary only because of the creation of the social organization itself—the adjudication of disputes among members and the defense of the city against external attacks, for example. Therefore, carrying the principle of specialization one step further, Plato proposed the establishment of an additional class of citizens, the guardians who are responsible for management of the society itself.
In fact, Plato held that effective social life requires guardians of two distinct sorts: there must be both soldiers whose function is to defend the state against external enemies and to enforce its laws, and rulers who resolve disagreements among citizens and make decisions about public policy. The guardians collectively, then, are those individuals whose special craft is just the task of governance itself.-Plato: The State and the Soul