A Nightmare for Lewisian Halfers
Preprint in PhilSci-Archive, 2026
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, it 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.
Recommended citation: Lennart B. Ackermans (2026). "A Nightmare for Lewisian Halfers". PhilSci-Archive preprint.
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