The structure of a theoretical system tells us what alternatives are open in the possible answers to a given question. If observed facts of undoubted… - Talcott Parsons

The most promising lines of development of theory in the sociological and most immediately related fields, particularly the psychological and cultural, therefore, seem to be two-fold. One major direction is the theoretical elaboration and refinement of structural-functional analysis of social systems, including the relevant problems of motivation and their relation to cultural patterns. In this process, the structure of social action provides a basic frame of reference, and aspects of it become of direct substantive importance at many specific points. The main theoretical task, however, is more than a refinement of the conceptual scheme of the presently reprinted book — it involves transition and translation to a different level and focus of theoretical systematization.

Ideology is a system of beliefs, held in common by the members of a collectivity.

Every social system is a functioning entity. That is, it is a system of interdependent structures and processes such that it tends to maintain a relative stability and distinctiveness of pattern and behavior as an entity by contrast with its - social or other - environment, and with it a relative independence from environmental forces. It "responds", to be sure, to the environmental stimuli, but is not completely assimilated to its environment, maintaining rather an element of distinctiveness in the face of variations in environmental conditions. To this extent it is analogous to an organism