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.