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Chapter 11 - The Relation between Degrees of Belief and Binary Beliefs

A General Impossibility Theorem

Published online by Cambridge University Press:  29 January 2021

Igor Douven
Affiliation:
Université Paris-Sorbonne
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Summary

Agents are often assumed to have degrees of belief (“credences”) and also binary beliefs (“beliefs simpliciter”). How are these related to each other? A much-discussed answer asserts that it is rational to believe a proposition if and only if one has a high enough degree of belief in it. But this answer runs into the “lottery paradox”: The set of believed propositions may violate the key rationality conditions of consistency and deductive closure. In earlier work, we showed that this problem generalizes: There exists no local function from degrees of belief to binary beliefs that satisfies some minimal conditions of rationality and nontriviality. “Locality” means that the binary belief in each proposition depends only on the degree of belief in that proposition, not on the degrees of belief in others. One might think that the impossibility can be avoided by dropping the assumption that binary beliefs are a function of degrees of belief. We prove that, even if we drop the “functionality” restriction, there still exists no local relation between degrees of belief and binary beliefs that satisfies some minimal conditions. Thus functionality is not the source of the impossibility; its source is the condition of locality. If there is any nontrivial relation between degrees of belief and binary beliefs at all, it must be a “holistic” one. We explore several concrete forms that this “holistic” relation could take.

Type
Chapter
Information
Lotteries, Knowledge, and Rational Belief
Essays on the Lottery Paradox
, pp. 223 - 254
Publisher: Cambridge University Press
Print publication year: 2021

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