"Functionalist systems theories. The theorists in this tradition explain the emergence and/or maintenance of parts, structures, institutions, norms or cultural patterns of a social system in terms of their consequences, that is, the particular functions each realizes or satisfies. This includes, for instance, their contribution to the maintenance and reproduction over time of the larger system. The major functionalist in sociology is arguably Talcott Parsons."

“System theories have been applied to a wide spectrum of empirical cases and policy issues. Parsons and his followers, in particular, applied their systems theory to diverse empirical phenomena in sociology as well as in other disciplines: modernization, economics, politics, social order, industrialization and development, Fascism and McCarthyism, international relations, social change and evolution, complex organizations, health care, universities, religion, professions, small groups, and family as well as abstract questions such as the place of norms in maintaining social order both historically and cross-nationally. Marxian theory and dynamic system theories have also been applied to a spectrum of diverse empirical and policy subjects.”

“Within sociology there have been several system theories, differing from one another in the extent to which, for example, human agency, creativity, and entrepreneurship are assumed to play a role in system formation and reformation; conflict and struggle are taken into account; power and stratification are part and parcel of the theory; structural change and transformation – and more generally, historically developments – are taken into account and explained. What the various system theories have in common is a systematic concern with complex and varied interconnections and interdependencies of social life. Complexity has been a central concept for many working in the systems perspective. The tradition is characterized to a great extent by a burning ambition and hope to provide a unifying language and conceptual framework for all the social sciences.”

“Among other related major developments, world systems theory should be mentioned. Inspired by Marxist theories, it addresses dependency among nations and imperialism, placing the evolution of capitalist systems in a global and comparative perspective. Another variant of Marxist system theory is that of Pierre Bourdieu which unifies the material and the symbolic, as well as agency and structure.”

“In sum, social actors knowledgeably and actively use, interpret and implement rule systems. They also creatively reform and transform them. In such ways they bring about institutional innovation and transformation and shape the ‘deep structures’ of human history.”

“In the most abstract sense, a system is a set of objects together with relationships among the objects. Such a definition implies that a system has properties, functions, and dynamics distinct from its constituent objects and relationships.”

“Actor-oriented, dynamic systems theories. This family of theories -- inspired to a great extent by Buckley -- is largely non-functionalist. It includes Buckley’s “modern systems theory,” Archer’s “morphogenetic” theory, Burns’ “actor-system-dynamics” , and the “” of Geyer and van der Zouwen . Complex, dynamic social systems are analysed in terms of stabilizing and destabilizing mechanisms, with human agents playing strategic roles in these processes. Institutions and cultural formations of society are carried by, transmitted, and reformed through individual and collective actions and interactions.”