Notes on neighborhood semantics for logics of unknown truths and false beliefs
This work addresses foundational problems in modal logic for epistemic reasoning, offering incremental theoretical advancements in expressivity and axiomatization.
The authors studied logics of unknown truths and false beliefs under neighborhood semantics, finding that these two logics are incomparable in expressivity over various model classes, and their combination is equally expressive as standard modal logic. They proposed morphisms, established soundness and completeness results, axiomatized the logics over different frames, and extended the findings to public announcements with applications to Moore sentences.
In this article, we study logics of unknown truths and false beliefs under neighborhood semantics. We compare the relative expressivity of the two logics. It turns out that they are incomparable over various classes of neighborhood models, and the combination of the two logics are equally expressive as standard modal logic over any class of neighborhood models. We propose morphisms for each logic, which can help us explore the frame definability problem, show a general soundness and completeness result, and generalize some results in the literature. We axiomatize the two logics over various classes of neighborhood frames. Last but not least, we extend the results to the case of public announcements, which has good applications to Moore sentences and some others.