Chapter 9 Representative democracy as social choice Social Choice traditionally employs the preferences of voters or agents as primitives. However in most situations of constitutional decision making the beliefs of the members of the electorate determine their secondary preferences or choices. Key choices in US political history such as the ratification of the Constitution in 1787 and the election of Lincoln in 1860 were conditioned by changing beliefs as regards the truth of propositions about the political universe. Preference based models of election tend to conclude that candidates or parties converge to a vote maximizing policy position at the “electoral center”. Empirical work suggests that such a conclusion is invalid. This chapter argues on the contrary that parties or candidates adopt positions that optimize in a Nash equilibrium sense with respect to both their beliefs over electoral response and their beliefs over appropriate policy choices. The analysis indicates that political choices will be different depending on whether plurality (“first past the post”) or proportionality is used as the method of electoral representation.