Theories of electoral institutions suggest that majoritarian and proportional systems will produce distinct patterns of party-voter congruence, with the centripetal incentives of the former pulling parties to the ideological center and reducing, by comparison with the latter, congruence with voters to the right and left. Recent scholarship, however, has found little contemporary empirical evidence for this pattern but no satisfactory explanation has been advanced to account for these non-findings. In this paper, we develop a new theoretical account of the impact of electoral institutions on congruence that takes into account the increasingly dealigned character of voters. Our central argument is that the impact of institutions is conditional on the balance between partisans and independents in the electorate. It is this conditional nature of the influence, we argue, that accounts for the absence of the anticipated relationship of institutions to congruence nowadays. We test this theory using a unique data set of party positions in 24 European states.
