Social Choice and Welfare

, Volume 31, Issue 1, pp 15–39 | Cite as

Judgment aggregation without full rationality

  • Franz Dietrich
  • Christian List
Original Paper


Several recent results on the aggregation of judgments over logically connected propositions show that, under certain conditions, dictatorships are the only propositionwise aggregation functions generating fully rational (i.e., complete and consistent) collective judgments. A frequently mentioned route to avoid dictatorships is to allow incomplete collective judgments. We show that this route does not lead very far: we obtain oligarchies rather than dictatorships if instead of full rationality we merely require that collective judgments be deductively closed, arguably a minimal condition of rationality, compatible even with empty judgment sets. We derive several characterizations of oligarchies and provide illustrative applications to Arrowian preference aggregation and Kasher and Rubinstein’s group identification problem.


Aggregation Function Full Rationality Agenda Condition Impossibility Result Judgment Aggregation 
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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of Quantitative EconomicsUniversity of MaastrichtMaastrichtThe Netherlands
  2. 2.Department of GovernmentLondon School of EconomicsLondonUK

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