The interdependence of social deliberation and judgment aggregation

Imagine that the judgments of some individuals on some issues are aggregated into collective judgments. Social deliberation about the issues prior to aggregation can lead to improved judgments, at both the individual and the collective level. In this paper I argue that the epistemic justification for a social deliberation design depends on the chosen judgment aggregation rule, and vice versa. This claim consists of two parts. First, the epistemic superiority of one deliberation design over another or over the absence of any deliberation depends on which procedure is subsequently used to aggregate individual judgments. Second, the epistemic superiority of one aggregation procedure over another depends on how the preceding social deliberation was designed. In short, the choice of deliberation design and of aggregation rule are intertwined. This claim is substantiated by two models. Both models display a tragic rise in competence: social deliberation raises individual competence while reducing collective competence. Here, individual and social epistemology come interestingly apart.