Mighty Belief Revision

Abstract

Belief revision theories standardly endorse a principle of intensionality to the effect that ideal doxastic agents do not discriminate between pieces of information that are equivalent within classical logic. I argue that this principle should be rejected. Its failure, on my view, does not require failures of logical omniscience on the part of the agent, but results from a view of the update as mighty: as encoding what the agent learns might be the case, as well as what must be. The view is motivated by consideration of a puzzle case, obtained by transposing into the context of belief revision a kind of scenario that Kit Fine has used to argue against intensionalism about counterfactuals. Employing the framework of truthmaker semantics, I go on to develop a novel account of belief revision, based on a conception of the update as mighty, which validates natural hyperintensional counterparts of the usual AGM postulates.

Hyperintensionality and overfitting

“…One may be tempted to adopt some hyperintensional view of content and do epistemic logic systematically on that basis. (E.g., for works recruiting Kit Fine's truthmaker semantics to do just that, see Krämer (2022); Hawke and Özgün (2023).) Under the label of 'overfitting', Sect.…”