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The degree of epistemic justification and the conjunction fallacy

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Abstract

This paper describes a formal measure of epistemic justification motivated by the dual goal of cognition, which is to increase true beliefs and reduce false beliefs. From this perspective the degree of epistemic justification should not be the conditional probability of the proposition given the evidence, as it is commonly thought. It should be determined instead by the combination of the conditional probability and the prior probability. This is also true of the degree of incremental confirmation, and I argue that any measure of epistemic justification is also a measure of incremental confirmation. However, the degree of epistemic justification must meet an additional condition, and all known measures of incremental confirmation fail to meet it. I describe this additional condition as well as a measure that meets it. The paper then applies the measure to the conjunction fallacy and proposes an explanation of the fallacy.

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Correspondence to Tomoji Shogenji.

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An early version of this paper was presented at the workshop Probability, Confirmation and Fallacies in Leuven, Belgium, in April 2008. I would like to thank its organizers Jeanne Peijnenburg, David Atkinson and Igor Douven, and the participants of the workshop for many stimulating discussions. Special thanks to David Atkinson, Branden Fitelson, and Theo Kuipers for extremely helpful post-conference correspondence. A shorter version of the paper was presented under the title “The Degree of Epistemic Justification is Not the Probability” at the American Philosophical Association’s Eastern Division Meeting in Philadelphia in December 2008. I would like to thank the commentators James Joyce and Brad Armendt, and the participants of the session for valuable discussions.

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Shogenji, T. The degree of epistemic justification and the conjunction fallacy. Synthese 184, 29–48 (2012). https://doi.org/10.1007/s11229-009-9699-1

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  • DOI: https://doi.org/10.1007/s11229-009-9699-1

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