序論　国際政治における合理的選択

抄録

In international relations (IR), wars and other seemingly “irrational” outcomes often happen. Does that mean that actors in international relations are “irrational”? There are two main ways to answer this question. On one hand, the psychological approach searches for conditions under which human rationality breaks down; on the other hand, the rational choice approach, the subject of this special volume of International Relations, accounts for “irrational” outcomes as a result of collective decision making while assuming that actors are rational in a minimal sense.
This introductory chapter starts by tracing how the rational choice approach has been accepted by the IR discipline in Japan. Despite the fact that the first introduction of game theory in this journal was in 1959, the number of articles that used rational choice or game theory remained limited. In the 1990s, however, some Japanese IR researchers who studied in the United States began to write monographs using game theory. Since then, the number of IR works applying game theory has steadily increased.
The chapter summarizes key concepts in the two rational choice approaches. In the utility maximization framework, actors’ preferences are taken as data, from which utility functions are derived. One of the key conditions for preferences to be rational is that preferences induce no cycle. Utility maximization is not enough to understand strategic interactions among rational actors, and hence there is a need for game theory. In game theory, the key concepts are players, payoffs and strategies. Games are presented either in normal form or in extensive form. Also, the concept of incomplete information is very important for understanding signaling, for example.
The last section summarizes the chapters in this special volume. Suzuki and Ishiguro open up the blackbox of domestic politics to clarify how foreign policy decisions are made and how they affect international outcomes. Iwanami, Hayashi, and Kohama use the concept of signaling to understand such varied aspects of international relations as peacekeeping by regional organizations, multilateralism, and individual self-defense, respectively. Chiba and Kagotani and Kimura build their rational choice models informally, yet they test their hypotheses rigorously, using quantitative data. Finally, the chapters by Hatakeyama and Choi demonstrate how rational choice can be reconciled with other approaches.
This introductory chapter concludes by expressing the wish that more and more researchers will start contributing to a fuller development of the rational choice approach to international relations in the future.