Incomplete Preferences Under Uncertainty: Indecisiveness in Beliefs versus Tastes


  • Efe A. Ok,

    1. Dept. of Economics, New York University, 269 Mercer Street, New York, NY 10012, U.S.A.;
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  • Pietro Ortoleva,

    1. Division of the Humanities and Social Sciences, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91105, U.S.A.;
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  • Gil Riella

    1. Departamento de Economia, Universidade de Brasília, Campus Darcy Ribeiro, Brasília, DF 70910-900, Brazil;
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    • Various discussions with Ozgur Evren and Peter Wakker have contributed to this work; we gratefully acknowledge our intellectual debt to them. We also thank the co-editor and three referees for their substantial comments, expository and otherwise, concerning this paper. Finally, we acknowledge the financial support of the C. V. Starr Center for Applied Economics at New York University.


We investigate the classical Anscombe–Aumann model of decision-making under uncertainty without the completeness axiom. We distinguish between the dual traits of “indecisiveness in beliefs” and “indecisiveness in tastes.” The former is captured by the Knightian uncertainty model, the latter by the single-prior expected multi-utility model. We characterize axiomatically the latter model. Then we show that, under independence and continuity, these two models can be jointly characterized by means of a partial completeness property.