Graphs for time and modality
As we have mentioned in part 2, C.S. Peirce established a calculatory technique of logical graphs. These so-called existential graphs have been studied carefully by computer scientists and others for some years. Since the beginning of the 1980’s, John Sowa  and others have tried to systematise a modern version of Peirce’s existential graphs — and indeed, to implement it computationally. (A somewhat different but also highly interesting modernisation is Harmen van den Berg’s ‘Knowledge Graphs’ [1993a].) It seems that the modern version of the Peircean graphs known as ‘conceptual graphs’ is useful within artificial intelligence in a broad sense — including interfaces to databases, deductive databases, and the like. In this chapter we shall study the Peircean ideas and some of the problems Peirce left open. We shall focus on the ‘graphical’ representation of tempo-modal problems.
KeywordsModal Logic Married Woman Epistemic Logic Tense Operator Conceptual Graph
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