# The study of relations rather than "entities" with an emphasis on process and transition probabilities as the basis of a flexible structure of many… - Walter F. Buckley

Social differentiation is a universal characteristic of human societies. Early human societies survived and became dominant among animal species because of their superior social organization — that is, their more elaborate division of labor and consequent close coordination of activities.

The more recent concern with complex adaptive organization has led to the notion of contingency as the important key. Thus Wiener, while working in the field of communications and probability theory, became convinced 'that a significant idea of organization cannot be obtained in a world in which everything is necessary and nothing is contingent'

In a class system, the social hierarchy is based primarily upon differences in monetary wealth and income. Social classes are not sharply marked off from each other, nor are they demarcated by tangible boundaries. Unlike estates, they have no legal standing, individuals of all classes being in principle equal before the law. Consequently, there are no legal restraints on the movement of individuals and families from one class to another... Unlike caste, social classes are not organized, closed groups. Rather, they are aggregates of persons with similar amounts of wealth and property, and similar sources of income.