In the 1940s, '50's and '60s, a version of functionalist theory, structural functionalism, became the central paradigm of sociology. Two American sociologists particularly stand out during this period: Robert Merton and his mentor Talcott Parsons. Talcott Parsons saw that people's conformity to social rules was not simply produced through the negative fear of punishment; instead, people conformed in positive ways, teaching others society's moral rules and norms of behavior. Such positive commitment to an orderly society showed, says Parsons, which social rules are not merely external force acting on individuals, but have become internalized via the continual process of socialization. Having established the primacy of a sociological understanding of social order, Parsons turned his attention to the functioning of the social system itself. To do this, he devised a model based on identifying the needs of the system, known as the AGIL paradigm.
Parsons argued that if a social system is to continue, then there are four basic functions it must perform. First, it must be capable of adapting to its environment and gather enough resources to do so. Second, it must set out and put in place goals to be attained and the mechanisms for their achievement. Third, the system must be integrated and the various sub-systems must be coordinated effectively. Finally, the social system must have ways of preserving and transmitting its values and culture to new generations. Parsons structural functionalism was a form of systems theory, which tended to give priority to the overall system and its 'needs'.