Talcott Parsons is the most outstanding exponent of the social system theory.In 'A Social System' his emphasis shifted from unit act to institutional orders but the system was the primary unit of analysis. According to Parsons a social system is a system of action which has the following characteristics
It involves a process of interaction between two or more actors; the interaction process as such is the focus of the observer's attention- the Act
The situation towards which the actors are oriented include other actors- the Actors
There is an interdependent and in part concerted action in which the concert is a function of collective goal orientation or common values and of a consensus of normative and cognitive expectations – the status and role.
The social system consists in a plurality of individual actors interacting with each other in a situation which has at least a physical or environmental aspect, actors who are motivated in terms of a tendency to the optimization of gratification and whose relation to their situations including each other is defined and mediated in terms of a system of culturally structured and shared symbols. It is the system of actions. It is the system of interdependent action processes. There are three aspects of the structuring of a complete concrete system of social action and these ares- the personality system of individual actors, the cultural system which is built into their action and the social system.