Talcott Parsons' concept of pattern variables bridges the gap between social action and social system .He defines these as the fundamental dilemmas that face actors in any situation. Social system may be characterised by the combination of solutions offered to these dilemmas.
These pattern variables structure any system of interaction. Such systems however also have certain needs of their own which have to be met as required both by relationship between the social system and its environment and by the internal workings of the system. There are four such functional needs functional needs known as AGIL-adaption, the need to relate to the environment by taking resources from it; goal attainment the setting of goals for the system; integration,the maintenance of internal order; latency or pattern maintenance, the generation of sufficient motivation to perform tasks. In order to meet each of these functional needs, groups of actions or subsystems of action develop. At the most general level the cultural subsystem performs the latency function and the social subsystem the function of integration. Each of these sub-systems is also faced by the same four functional needs and consequently each sub-system can be divided into 4 subsystems. In the social system as a whole, the economy performs the function of adaptation.