Maurice Duverger made seminal contributions to at least two related, and yet still distinct, literatures. On the one hand, Duverger's Law remains a central touchstone of the electoral systems and party systems literatures. On the other hand, Duverger is also a seminal figure in the literature concerning the organization of individual parties. In particular, although he directly associated the idea of the mass party with parties of the left, through his idea of "contagion from the left" Duverger has become identified with the idea that the mass party was not just AN organizational form, but THE organizational form of the future. While Duverger's Law is easily understood as a rational choice argument, both from the perspective of parties and from the perspective of citizens, the mass party argument, on the other hand, is much more in the early 20th century European tradition of "sociological determinism". In this intervention I consider the degree to which these two contributions are in tension with one another - and what difference that might make for how we understand the impact of Duverger's Law.
