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A Nightmare for Lewisian Halfers

Ackermans, Lennart B. (2026) A Nightmare for Lewisian Halfers. [Preprint]

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Abstract

What if Sleeping Beauty has dreams? I give an argument against the halfer position that only uses principles of rationality accepted by Lewisian halfers. While dreaming, Beauty’s credence in heads is 1/2. After being woken up and updating on the evidence that she is woken up today, the credence becomes less than 1/2. For Lewisian halfers, this is a nightmare. If we add two plausible assumptions about Beauty’s dreaming credences, we can derive the thirder solution. I also respond to and improve upon a new type of defence of Lewisian halfing by Schwarz (2025), but argue that it fails as well.

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Item Type: Preprint
Creators:
CreatorsEmailORCID
Ackermans, Lennart B.philosophy@ackermans.ch0000-0003-0071-2270
Keywords: Sleeping Beauty, Lewisian halfism, self-locating evidence, Bayesian conditionalization, expected accuracy
Subjects: General Issues > Decision Theory
Specific Sciences > Probability/Statistics
Depositing User: Lennart Ackermans
Date Deposited: 14 Jun 2026 13:58
Last Modified: 14 Jun 2026 13:58
Item ID: 30110
Subjects: General Issues > Decision Theory
Specific Sciences > Probability/Statistics
Date: 13 June 2026
URI: https://philsci-archive.pitt.edu/id/eprint/30110

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