Unpacking the Second Chamber Incongruence: A New Classification of Bicameral Parliaments

Out of the 52 democratic countries with more than one million inhabitants, 28 have bicameral parliaments. Within this sub-group, though, differences are remarkable. While lower houses have similar powers across countries and are all directly elected, Senates range from largely ceremonial organs to organs with powers similar to those of the lower house; sometimes they are directly elected, sometimes they are appointed by other institutions, or a mix of the two. When directly elected, the electoral rules are sometimes similar sometimes quite different to those in place for the lower house. Political science has devoted much attention to these issues, proposing several ways to classify different kinds of bicameralism. Largely accepted classifications are based on the degree of “congruence in composition” and “symmetry of powers” between the two chambers. In this paper we propose minor specifications to the conventional analysis of symmetry, dispute the existing definitions of congruence and propose a novel classification. We argue that congruence has been mismeasured and that it is conceptually misleading. According with a revisited version of the veto players approach, we suggest that the concept of congruence should be clarified and unpacked. Among the institutional determinants of incongruence, we distinguish those that tend to shrink from those that tend to enlarge - in the upper chamber - the minimal winning coalitions potentially formed in the lower. We show that our classification overcomes some limits and contradictions of existing ones. We also bring empirical evidence that it is better suited to understand the nature of bicameral parliaments and the impact of different forms of bicameralism on the executive-legislative relations. We finally argue that it better frames the normative and prescriptive debate over the justification of bicameralism.