A model of deliberative and aggregative democracy

Abstract

We present a model of collective decision making in which voting and deliberation are treated simultaneously. Political theorists argue that public discussion can lead individuals to change their preferences. This aspect of democracy is typically ignored in models of social choice that focus exclusively on voting. In our model, individuals debate in a public forum and potentially revise their preferences in light of deliberation. Once this process is exhausted, a voting rule is applied to aggregate post-deliberation preferences into a social choice. Restricting attention to three alternatives, we identify conditions under which a democracy is truth-revealing in the sense that the deliberation path and the voting rule will always lead to the correct social choice being made, irrespective of the original profile of preferences and size of the electorate (provided the latter is finite). A critical parameter in the model is the persuasion cost. When this is low, a democracy is almost always truth-revealing. When it is high, we have the standard social choice model and truthful revelation is impossible. Moreover, we identify when and only when truthful revelation occurs in an interesting intermediate case.