In defiance of Duverger: The class cleavage and the emergence of district-level multiparty systems in western Europe

At its core, Duverger’s Law, which holds 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. A growing body of research, however, shows that district-level party system fragmentation can indeed exceed two in first-past-the-post systems. This piece addresses the fundamental tension between Duverger’s Law and recent scholarship on district-level party systems. I explore whether the major alternative explanation for party system fragmentation – the social cleavage approach – can explain 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, in defiance of Duverger, greater levels of social cleavage diversity may produce multiparty systems even in first-past-the-post systems