Gamma graph calculi for modal logics

Minghui Ma

Pietarinen

pp. 3621-3650

in: Hanoch Ben-Yami, Robyn Carston, Markus Werning (eds), Trends in philosophy of language and mind, Synthese 195 (8), 2018.

Abstract

We describe Peirce’s 1903 system of modal gamma graphs, its transformation rules of inference, and the interpretation of the broken-cut modal operator. We show that Peirce proposed the normality rule in his gamma system. We then show how various normal modal logics arise from Peirce’s assumptions concerning the broken-cut notation. By developing an algebraic semantics we establish the completeness of fifteen modal logics of gamma graphs. We show that, besides logical necessity and possibility, Peirce proposed an epistemic interpretation of the broken-cut modality, and that he was led to analyze constructions of knowledge in the style of epistemic logic.

Cited authors

Peirce Charles Sanders