Rationalism and the “rational actor assumption” in realist international relations theory

The commitment to the rational actor model of state behavior is said to be a core assumption of realist theory. This assumption is listed in most textbook accounts of realism. Yet is rationality a core supposition of realist theory, and if so, what kind of rationality is implied in these claims? Debate on the relationship between realism, and what is often labeled as rationality is replete with misunderstandings. Authors deploy terms such as rationality, rationalism, and rational actor in diverse and contradictory ways. This article aims to cut through this confusion and provide an account of the different ways in which these terms are used in the field of International Relations (IR). We argue that much of the confusion surrounding rationalism/rationality in IR arises due to a failure to distinguish between rationalism as an epistemological position (the observer rationality assumption) and rationality as an ontological position (the rational actor assumption). We use this distinction to examine carefully the relationship between the concepts of rationalism/rationality in realist theory.