Tharp's theorems of metaphysics and the notion of necessary truth

Jordan Stein

pp. 1219-1231

in: Sune Holm, John Basl (eds), Teleological organisation, Synthese 194 (4), 2017.

Abstract

Leslie Tharp proves three theorems concerning epistemic and metaphysical modality for conventional modal predicate logic: every truth is a priori equivalent to a necessary truth, every truth is necessarily equivalent to an a priori truth, and every truth is a priori equivalent to a contingent truth. Lloyd Humberstone has shown that these theorems also hold in the modal system Actuality Modal Logic (AML), the logic that results from the addition of the actuality operator to conventional modal logic. We show that Tharp’s theorems fail for the expressively equivalent Subjunctive Modal Logic (SML), the logic that was developed by Kai Wehmeier as an alternative to AML. We then argue that the existence of Tharp’s theorems for AML is due to a faulty interpretation of the notion of necessary truth, a feature that is not shared by SML. The paper concludes with an argument for the thesis that the existence of the distinction between truth at all worlds w and truth at all worlds w from the point of view of w as the actual world is an artifact owing to the interaction of the necessity and actuality operator.

Cited authors

Humberstone Lloyd

Wehmeier Kai

Tharp Leslie