Organon F

Volume 26, August 2019, Issue 3, Pages 474–490

ISSN 2585-7150 (online) ISSN 1335-0668 (print)

Research Article | Special issue on Reflecting on the Legacy of C.I. Lewis: Contemporary and Historical Perspectives on Modal Logic

Wiredu contra Lewis on the Right Modal Logic

David B. Martens


This paper is a critical study of an argument put forward by Kwasi Wiredu in his engagement with C. I. Lewis on choosing the right modal logic for logical necessity. Wiredu argues that Lewis “could have been more adventurous modally with perfect logicality” and could justifiably have accepted S4 rather than being “to the last cautious of any system stronger than S2” (Wiredu 1979). I address terse, incomplete, and provocatively incongruous notes on Wiredu’s paper by (Makinson 1980) and (Humberstone 2011), as well as a paper by (Cresswell 1965) that Humberstone cites, and I draw on recent work by (Lewitzka 2015; 2016). I conclude that Wiredu’s argument cannot be accepted as sound but a variant argument can be accepted as sound.


C.I. Lewis, equivalence, identity, Kwasi Wiredu, modal logic, S4.

Author(s) and affiliation(s)


David B. Martens


University of the Witwatersrand


Department of Philosophy, School of Social Sciences, University of the Witwatersrand, Johannesburg, Private Bag 3, WITS 2050, South Africa


About this article


31 October 2018


2 March 2019

Published online

24 August 2019


Institute of Philosophy of the Slovak Academy of Sciences

Institute of Philosophy of the Czech Academy of Sciences

Cite as


Martens, D.B. (2019). Wiredu contra Lewis on the Right Modal Logic. Organon F, 26(3), 474–490.


Martens, David B. 2019. "Wiredu contra Lewis on the Right Modal Logic." Organon F 26 (3): 474–490.


Martens, D.B. (2019). Wiredu contra Lewis on the Right Modal Logic. Organon F, 26(3), pp. 474–490.

Copyright information

© David B. Martens

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