2007 年 22 巻 p. 96-106
The electoral reform adopted by Japan in 1994 features single-member districts, though it also includes a proportional representation (PR) tier. Many hoped, based on one of political science's most reliable generalizations, Duverger's Law, that the new system would foster a two-party system. I argue that it has indeed done so. Using many different indicators of the existence of a two-party system, I find that the Japanese party system has gotten closer to bipolarity at each successive election, and now surpasses the archetypical two-party system, Great Britain, on some indicators. Interestingly, the PR tier, far from reducing the power of Duverger's Law, seems to have enhanced its operation. I also speculate about the future and the possibility of an alternation in power.