List: *Cognito: Revista de Filosofia* has finally published its special issue on "Peirce and Logics" ( https://revistas.pucsp.br/index.php/cognitiofilosofia/issue/view/3060), which includes a contribution from me, "Peirce and Modal Logic: Delta Existential Graphs and Pragmaticism" ( https://revistas.pucsp.br/index.php/cognitiofilosofia/article/view/60449/46975). Here is the abstract.
Although modern modal logic came about largely after Peirce’s death, he anticipated some of its key aspects, including strict implication and possible worlds semantics. He developed the Gamma part of Existential Graphs with broken cuts signifying possible falsity, but later identified the need for a Delta part without ever spelling out exactly what he had in mind. An entry in his personal Logic Notebook is a plausible candidate, with heavy lines representing possible states of things where propositions denoted by attached letters would be true, rather than individual subjects to which predicates denoted by attached names are attributed as in the Beta part. New transformation rules implement various commonly employed formal systems of modal logic, which are readily interpreted by defining a possible world as one in which all the relevant laws for the actual world are facts, each world being partially but accurately and adequately described by a closed and consistent model set of propositions. In accordance with pragmaticism, the relevant laws for the actual world are represented as strict implications with real possibilities as their antecedents and conditional necessities as their consequents, corresponding to material implications in every possible world. I originally submitted this paper more than two years ago, and subsequently wrote "Enhancing Existential Graphs: Peirce's Late Improvements" ( https://muse.jhu.edu/article/939654) as its sequel, but the latter ended up appearing in *Transactions of the Charles S. Peirce Society* first. Discussion of either or both would be welcome. Regards, Jon Alan Schmidt - Olathe, Kansas, USA Structural Engineer, Synechist Philosopher, Lutheran Christian www.LinkedIn.com/in/JonAlanSchmidt / twitter.com/JonAlanSchmidt
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