In the 1950s and 1960s, under the aegis of such scholars as Talcott Parsons and R.K. Merton, functionalism became a fundamental part of sociological and political explanation. It influenced theoretical and methodological attempts to explain the conditions and factors which make a political system work. For example, systems theory , as expounded by David Easton and others, modelled the political decision-making process as a system of inputs, outputs and feedback loops which lead to the creation of binding agreements. Other political scientists developed functional frameworks for the comparative analysis of different political systems by distinguishing between system, process and policy functions which institutions perform. Functionalist 'explanation' is criticized on philosophical and normative grounds.
Philosophical critics complain that functional explanation is circular.
It confuses the consequences of an action with its causes. They also complain that functional explanations lack causal mechanisms to give them plausibility. For example, if a political scientist declares that the fragmented pattern of quasi-governmental agencies is explained by its functional consequences for a capitalist economy, he or she has given us no account of how, or why, this result is achieved. For example, if priests conduct rain-dances because they believe it will produce social cohesion among tribal members we have an intentional explanation of the phenomenon, and we do not require a functionalist account. He maintains that very few so-called functionalist explanations meet these requirements.