CEFISES Seminar: Peter Verdée, “Ground-theoretic semantics: reasons and propositions”

Livestream  https://youtu.be/KnKnePxvuvU

Series: WIP

Abstract: In this talk I will present some recent progress in the project of developing ground-theoretic semantics. More concretely I will show how (formal) ground-theoretic semantics can be interpreted as individuating the meaning of sentences by the set of the reasons that might be given for their truth and the reasons that might be presented for their falsity in any possible world. The ground-theoretic clauses of the semantics dictate how reasons for semantically simple expression result in reasons for semantically complex expressions. A full reason always contains a conventional (having to do with the meaning) and a substantial part (having to do with the way the world is). We naturally get two kinds of equivalence: (1) sense-equivalence; two sentences are sense-equivalent if their reasons are substantially the same and (2) synonymy; two sentences are synonymous if their reasons are fully identical. If we look at the corresponding equivalence classes we get two kinds of explications of the notion of proposition: corresponding to sense-equivalency we get what we call a sense proposition and corresponding to synonymy we get structured propositions. Both are hyperintensional.​

The talk of reasons is made precise along the following lines. We set up a mereological state space, the states playing the role of reasons. Each primitive sentences gets a set of verifiers and falsifiers, those are the positive and negative substantial reasons for that sentence, which are immediately also their full reasons. Each grounding rule also gets a non-empty set of verifiers. A full positive/negative reason for a sentence is obtained by considering a grounding rule for the truth/falsity of that sentence, and then fusing the full reasons for the grounds (given that rule) with a verifier for the grounding rule.

I will argue in favor of the philosophical usefulness of both kinds of propositions. First, the sense propositions give a reasonable formalization of Fregean senses in a way that is compatible with seeing proper names and indexicals as rigid designators. Second, the sense propositions allow characterizing an exact implication (on the constructive side) and an analytic implication (on the destructive side). Third, the structured propositions (with a specific inclusion relation) allow the definition of an interesting notion of non-factive grounding (on the constructive side) and a notion of conceptual essence (on the destructive side). All four of those implication notions are interestingly different from the existing proposals in the literature.