Duverger's Law and the Study of Electoral Systems

Since its first publication in 1951, Duverger’s Political Parties has influenced an entire branch of political science devoted to the study of the political consequences of electoral laws. This essay examines the two propositions known as Duverger’s law and Duverger’s hypothesis, both concerned with how electoral institutions shape party systems. First explaining the propositions and their context, the essay examines their influence on political science, and concludes by assessing where future research in the area might be best concentrated. French Politics (2006) 4, 69–83. doi:10.1057/palgrave.fp.8200092 Keywords: electoral systems; Duverger’s law; party systems; electoral studies ‘A law is valuable not because it is law, but because there is right in it ’ — Henry Ward Beecher. ‘Laws are like cobwebs, which may catch small flies but which let wasps and hornets break through ’ — Jonathan Swift. Duverger’s Law Among students of electoral systems, there is no better-known, more investigated, nor widely cited proposition than the relationship between plurality electoral laws and two-party systems known as Duverger’s Law. Since its publication more than a half-century ago in Political Parties (1951), hundreds of articles, books, and papers have been written to elaborate the workings of Duverger’s propositions. This growing literature has produced numerous empirical studies to explain how electoral systems and changes in electoral rules influence the number of political parties which compete for and win office. A parallel effort among formal theorists has led to many insightful works attempting to derive these empirical regularities from first principles, and otherwise to explore further the relationship between electoral rules and the number of political parties. The literature on formal and comparative electoral systems research is far too vast to review here, and indeed has been70 Kenneth Benoi