In Defiance of Duverger: The Class Cleavage and the Emergence of District-Level Multiparty Systems in Western Europe

At its core, Duverger's Law - holding that the number of viable parties in first-past-the-post systems should not exceed two - applies primarily at the district level. While the number of parties nationally may exceed two, district-level party system fragmentation should not. Given that a growing body of research shows that district-level party system fragmentation can indeed exceed two in first-past-the-post systems, I explore whether the major alternative explanation for party system fragmentation - the social cleavage approach - can explain such violations of Duverger's Law. Testing this argument in several West European elections prior to the adoption of proportional representation, I find evidence favouring a social cleavage explanation: with the expansion of the class cleavage, the average district-level party system eventually came to violate the two-party predictions associated with Duverger's Law. This suggests that sufficient social cleavage diversity may produce multiparty systems in other first-past-the-post systems.