Extension in The Port Royal Logic

John N. Martin

South American Journal of Logic, 2017, in press

http://www.sa-logic.org/aaccess/john-martin-extension-in-the-port-royal-logic.pdf

Abstract

This paper is a discussion of the meaning of extension in Arnauld and Nicole’s Logic or the Art of Thinking. Contrary to the reading of Jean-Claude Pariente, who reads an idea’s extension “intentionally” as the ideas defined in its terms, the paper defends a “referential” interpretation in which an idea’s extension, although a set of ideas, tracks the objects that the idea signifies in the world. Pariente’s reading makes truth a function of conceptual inclusion. The referential reading insures a correspondence theory of truth. It is argued that both readings account for essential truths, but only the referential reading accommodates the Logic’s commitment to contingent truth, sensation as part of the scientific method, the truth-conditions for categorical propositions, and the Logic’s account of false ideas and error. It is argued that, contrary to Pariente’s reading, the subject terms of true affirmative categorical propositions carry existential import.