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Published June 2016 | Published
Journal Article Open

Updating on the Credences of Others: Disagreement, Agreement, and Synergy


We introduce a family of rules for adjusting one's credences in response to learning the credences of others. These rules have a number of desirable features. 1. They yield the posterior credences that would result from updating by standard Bayesian conditionalization on one's peers' reported credences if one's likelihood function takes a particular simple form. 2. In the simplest form, they are symmetric among the agents in the group. 3. They map neatly onto the familiar Condorcet voting results. 4. They preserve shared agreement about independence in a wide range of cases. 5. They commute with conditionalization and with multiple peer updates. Importantly, these rules have a surprising property that we call synergy — peer testimony of credences can provide mutually supporting evidence raising an individual's credence higher than any peer's initial prior report. At first, this may seem to be a strike against them. We argue, however, that synergy is actually a desirable feature and the failure of other updating rules to yield synergy is a strike against them.

Additional Information

© 2016, Easwaran, Fenton-Glynn, Hitchcock, and Velasco. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License. We would like to thank David James Barnett, Paul Bartha, Richard Bradley, Seamus Bradley, Liam Kofi Bright, Mark Colyvan, Antony Eagle, Alan Hájek, Dennis Lehmkuhl, Leon Leontyev, Bradley Monton, Hendrik Rommeswinkel, Paulina Sliwa, Julia Staffel, Michael Titelbaum, Peter Vranas, and two anonymous referees for Philosophers' Imprint; as well as audience members at the 2013 Australian Association of Philosophy annual meeting in Brisbane, the University of Wisconsin-Madison, the University of North Carolina at Chapel Hill, the London School of Economics and Political Science, and the 2015 meetings of the Society for Exact Philosophy and the Formal Epistemology Workshop.

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August 20, 2023
October 20, 2023