David Truman on Democratic Efficiency
The incomplete incorporation of nonparty groups into explanations of the dynamics of democratic politics has many and complicated causes. One of them, however, probably lies in the nineteenth-century heritage, largely English, that the study of politics shares with economics. In crude terms the classical theories in both fields implicitly or explicitly started from the isolated individual. Both economic man and political man, it was assumed, exercised rational choice and acted independently for the maximization of individual advantage. No one man, behaving in this fashion, could affect significantly the general result, whether it was a governmental policy or a price in the market; only the aggregate of individual behaviors was determining. Deviations from these behaviors were increasingly recognized by both economists and political scientists, but for a long time they were treated as pathology rather than as evidence that the underlying theory did not account for the observed facts. The values associated with these theories were heavily loaded with emotion, and modification was therefore both a slow and a painful process. The reconstruction of classic explanations to accommodate group behavior [i.e. mediating institutions] has been common in recent years, however, to both economics and politics, although in the latter field it has proceeded rather slowly.
David Truman, The Governmental Process: Political Interests and Public Opinion