Political systems are recursive structures that process political demands and supports and transform them into decisions for the authoritative allocation of values in society. The concept was first formulated in the 1950s by political scientist David Easton who has been described as one of the “first generation of behavioral revoutionaries” in political science. The political systems perspective is deeply interwoven with Easton’s widely accepted definition of politics as "the authoritative allocation of values in society."
According to Easton, political systems can be analyzed in terms of inputs, processes and outputs. Political inputs, he suggested are of two basic types: demands (for action, for concrete benefits or for other political outputs) and supports (votes, ideological loyalty, party membership, donations, and the like). These inputs are processed by the political system to generate outputs in the form of authoritative decisions allocating values.
The model, like other products of the behavioral movement in political science, is largely positivist in orientation. According to Gunnell (1983), Easton sought to establish a general theory of political science in the form of a deductive system so that the largest possible number of empirically-grounded generalizations could be deduced from a single framework. Bevir (2006) attributes to Easton’s theorizing an effort to gain a measure of control and order over the rapidly increasing and increasingly disorderly body of political science research results.  To a considerable degree the political systems model was successful in this objective, as analysts could, for example, compare demands, supports and the resulting decisions in executive and legislative systems. Also, when coupled with more process-oriented models, such as Robert Dahl’s policy process model arising out of studies of local government in New Haven, Connecticut, it became increasingly possible to systematically collate results from different political studies beginning with the demands and supports all the way through to the authoritative decisions they provoked.
Equally important was the inclusion of a feedback loop like those characteristic of most systems models of the time. In the case of political systems, the feedback loop introduced a critically important time dimension and raised a broad range of interesting possibilities and questions regarding the impact of previous decisions on current patterns of political demand and support, and the impact of current decisions on future demands and supports.
In the following decade, another American political scientist, Thomas R. Dye, took political systems theory to another level introducing a new layer of macro-political inputs associated with urbanization, industrialization and bureaucratization and treating outputs in terms of the empirical consequences flowing from decisions. In the Dye political systems model, the earlier Easton model was easily and completely subsumed within the middle, political process, term.
In sum: social and economic inputs such as urbanization and industrialization acted upon populations to produce certain patterns of political demand and support, which formed the inputs to the political system, and produced decisions (systemic outputs) which resulted in further distributions of benefits, establishment of programs and services and other outcomes. Both decision outputs and programmatic outcomes originated feedback loops, so that both decisions and the consequences of programs were seen as producing consequences for social conditions (summarized by urbanization and industrialization) which in turn further altered the patterns of demands and supports. And so, cycles of the political system continued in multiple iterations.
The Easton and Dye political systems models were the basis of a substantial number of research studies in the second half of the twentieth century, and served as the basis for a number of textbooks and research summaries. In general, however, it does not appear that the political systems model has yet proved to be the source of an integrated deductive theoretical system of the type Easton originally envisioned.
A multi-level concept
One of the virtues of the Easton political systems model is that it works at a number of different levels. Thus, for example, electoral systems function as political systems to translate demands (e.g. exercising the right to vote) and supports (e.g.the legitimacy of a system allowing citizen participation in this form) into authoritative decisions (the election of one candidate and the defeat of others.), which leads in turn to eventual demands to vote in future elections in order to maintain the legitimacy of the system, and so forth.
- Ball, Terrence. ”Political theory and political science: Can this marriage be saved?“ Theoria: Journal of Political and Social Theory. 113. August, 2007. 1-22.
- Gunnell, John G. 1983. "Political Theory: The Evolution of a Subfield." Ada W. Finifter, Ed. Political Science: The State of the Discipline. American Political Science Association: Washington, DC, p. 19.
- Bevir, Mark. 2006. Political studies as narrative and science, 1880-2000. Political Studies. (October). 583-606.