It is no longer in style to develop typologies of political regimes based on their party systems. Systematic studies today are interested in parties only in terms of their role in the functioning of the political system as a whole. No doubt it is an insoluble problem to determine whether parties and the party system are variables which are independent or dependent in relation to the political system. Besides, without being able to rule out a relationship of interdependence, the two terms display a certain degree of independence and are not in a relationship of co-variance. Thus it is that the political system is shaped to a certain extent by the opposition of the parties to the system, the parties in turn having been conditioned by three other kinds of forces.

The problem of specifying the functions of parties remains a central one, even though there is much confusion in the use of the language of functionalism. It is therefore important to clarify the notion of the functions of political parties. If one defines the political system as a set of processes and mechanisms which bring about the convergence or neutralization of irresistible social pluralisms without exploding the balance of these pluralist forces, then one can distinguish three functional requirements: (1) the legitimation-stabilization function; (2) the tribunician function (integration or neutralization of centrifugal forces); (3) the function of providing governmental alternatives.

Where there is interaction between parties and the political system, one can discern an aspect of non-dependence between the two terms. In the first place, the parties (and not only the anti-system or revolutionary parties) do not develop solely in accordance with their relationship to the political system. Secondly, the system too has a certain degree of self-determination, even when confronted with anti-system parties.

After indicating that no rigorous political theory of groups exists, chiefly because interest groups are not genuine groups in the sense of “real collective units,” the author examines the disadvantages and advantages of using the systems analysis approach for the study of political parties and interest groups. Three correctives are suggested to systems theory, as it has been developed by a number of authors and more especially by David Easton, to make it better suited for the analysis of parties and interest groups. First, the environment must be made operational by the introduction, in addition to the political system, of a social system, providing constraints on the analyst comparable to those of the political system itself, and by the identification within both systems of a social and a political dynamic. Second, greater attention must be given to the way in which parties and interest groups, inasmuch as they act as input mechanisms, permit interactions between the social and the political systems. Third, a sharper focus must be put on the way the input function of political systems throws light on the life of groups.