Abstract
Sections 1 and 2 respectively raise and settle the question of whether, if an affirmative modality collapses (reduces to the null modality, that is) in a normal modal logic, then all modalities of the same length collapse in that logic, while Section 3 considers some special cases of an analogous phenomenon for congruential modal logics, closing with a general question about collapsing modalities in this broader range of logics.
Citation
Lloyd Humberstone. "Collapsing Modalities." Notre Dame J. Formal Logic 50 (2) 119 - 132, 2009. https://doi.org/10.1215/00294527-2009-001
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