This paper argues that governments formed from post–election coalitions (majority coalition governments in PR systems) and pre–election coalitions (majority parties in SMD systems) aggregate the interests of voters in systematically different ways. We show that the multiple policy dimensional policy space that emerges from PR motivates parties in the government coalition to logroll projects among themselves without internalizing the costs in the way that a majoritarian party would. We further show that, although centrifugal electoral incentives dominate in PR systems, some incentives towards coalescence across groups and across parties exist through the greater likelihood that large parties have in becoming a member of a minimal winning coalition of parties. The model predicts that the size of the public sector should should be larger in PR systems. This prediction is tested using data from the 1970's–90's in 17 European countries.