Sleeping Beauty and the demands of non‐ideal rationality

Abstract

If an agent can't live up to the demands of ideal rationality, fallback norms come into play that take into account the agent's limitations. A familiar human limitation is our tendency to lose information. How should we compensate for this tendency? The Seeping Beauty problem allows us to isolate this question, without the confounding influence of other human limitations. If the coin lands tails, Beauty can't preserve whatever information she has received on Monday: she is bound to violate the norms of ideal diachronic rationality. The considerations that support these norms, however, can still be used. I investigate how Beauty should update her beliefs so as to maximize the expected accuracy of her new beliefs. The investigation draws attention to important but neglected questions about the connection between rational belief and evidential support, about the status of ideal and non‐ideal norms, about the dependence of epistemic norms on descriptive facts, and about the precise formulation of expected accuracy measures. It also sheds light on the puzzle of higher‐order evidence.