Notre Dame Journal of Formal Logic

Modal Logics in the Vicinity of S1

Brian F. Chellas and Krister Segerberg


We define prenormal modal logics and show that S1, S1$^\circ$, S0.9, and S0.9$^\circ$ are Lewis versions of certain prenormal logics, determination and decidability for which are immediate. At the end we characterize Cresswell logics and ponder C. I. Lewis's idea of strict implication in S1.

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Notre Dame J. Formal Logic Volume 37, Number 1 (1996), 1-24.

First available in Project Euclid: 16 December 2002

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Zentralblatt MATH identifier

Primary: 03B45: Modal logic (including the logic of norms) {For knowledge and belief, see 03B42; for temporal logic, see 03B44; for provability logic, see also 03F45}


Chellas, Brian F.; Segerberg, Krister. Modal Logics in the Vicinity of S1 . Notre Dame J. Formal Logic 37 (1996), no. 1, 1--24. doi:10.1305/ndjfl/1040067312.

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