Up to now we have been describing the nature of the political system. Every political system has a definite form. Like every social system, it is a definite mode of behaviour, which can be actually observed. It consists of various units, called structures. A structure is a unit of behaviour or interaction which is regularly performed and is actually observable. For example a court, is a unit of interaction (or behaviour) between a judge, an advocate, witnesses and clients? Ordinarily a court is called an institution. But in system analysis it is called a structure. Here we are not interested in the legal rules which govern its working, but in the actual behaviour or interaction between its units which is regularly performed. It is an operational concept, and can be tested and verified by empirical or experimental methods.
Every structure consists of units, which are called roles, e.g. the role of a judge or of an advocate. A role is the particular part of the activity of the individual who are involved in a political process. Every individual performs several roles, but only that role is political which is performed in political processes. The political role is the basic unit of the political system. A role is neither a rule nor a norm, because it is only the observable behaviour of an individual. A rule or a norm may influence the behaviour of the individual, but it rarely describes it fully. For instance, the behaviour of a judge in the court is governed by the rules, but it is his role is his actual and observable behaviour, that is much more than what is covered by the rules.
Every political system is subject to a particular change, viz., the change of personnel. That is to say, the individuals who perform political roles may die or leave them; hence new individuals have to be recruited or enrolled to perform these roles. This is the recruitment function of the political system, which alone makes possible for it to continue to exist over time. The new individuals may, however, not perform their roles in the same way as did their predecessors. Thus with the change of the personnel, the political system is subject to change. It means that the new individuals have to be trained to perform the roles in the manner as expected of them.
Roles and Structural Differentiation:
A political system is subject to another kind of change, that is, the differentiation of roles and structures. It is its developmental phase. By differentiation of roles and structures we mean the development of new roles and structures, the transformation of the older ones into new ones and, the growth of new relationship between the roles and between structures or sub-systems. “In speaking of the developmental aspect of role and structure then, we are interested not only in the emergence of new types of rules or the atrophy of old ones, but also in the changing patterns of interaction among roles, structures, and sub-systems”.