Economics Imperialism and Solution Concepts in Political Science

Political science and economic science … make use of the same language, the same mode of abstraction, the same instruments of thought and the same method of reasoning (Black 1998, p. 354). Economics imperialism refers to the application of (mainstream) economic methods to the study of phenomena outside the traditional domain of economics. Uskali Mäki (forthcoming) has recently presented a typology of different aspects of economics imperialism in this journal. Economics expansionism is 'a matter of persistent pursuit to increase the degree of unification and full consilience provided by an economic theory by way of applying it to new types of phenomena.' Economics imperialism 'is a form of economics expansionism where the new types of explanandum phenomena are located in territories that are occupied by disciplines other than economics.' 2 (ibid.) 1 For many of its proponents, economics imperialism is thus a matter of unification. Mäki also argues that economics imperialism is in principle justifiable precisely due to this unificatory potential. However, he distinguishes between two kinds of unification, derivational and ontological. Derivational unification is a matter of deriving large classes of explanandum sentences from a parsimonious set of theoretical sentences or inference patterns. Ontological unification i n v o l v e s r e-describing large classes of apparently independent explanandum phenomena as forms or m anifestati ons of a comm on system of enti ties and causes. Mäki argues that derivational unification has value only if it is accompanied by ontological unification, and that the requirement of ontological unification should therefore be seen as a constraint on economics imperialism. In this paper we take a philosophy of science perspective on an important and prominent example of economics imperialism, the rational-choice branch of political science. Standard economic models rely on some solution concept (equilibrium) for deriving the implications of the model and rational behaviour as an apparently common causal postulate. Equilibrium might thus qualify as a common derivational element, and rationality as a common causal element in all rational-choice models. The following quotation from Duncan Black shows that practitioners of rational-choice political science consider economics and political science intimately related to each other through the shared concept of equilibrium: 1 Mäki proposes using the term 'economics imperialism' instead of the more common 'economic imperialism' because it makes clear the difference between the imperialism of theoretical approaches and the imperialism of nations or capitalist market-economy. We adopt Mäki's terminology because …