A Logic of von Wright’s Deontic Necessity

Studies in Logic, Vol. 15, No. 3 (2022): 1–17   PII: 1674-3202(2022)-03-0001-17

Jie Fan

Abstract.

In this paper, we build a bridge between G. von Wright’s deontic logic and E. Bezerra and G. Venturi’s ⊞-logic, in the sense that on one hand, we give an interpretation of ⊞-operator as von Wright’s deontic necessity, and on the other hand, we give the exact semantics of von Wright’s deontic modalities. Inspired by an almost definability schema, we explain why the canonical model of the minimal ⊞-logic is defined in that way. We also present various axiomatizations of ⊞-logic, among which the transitive system is also inspired by the schema in question. We explain why the two non-equivalent semantics for ⊞ involved in the literature, one of which is standard and the other is non-standard, come to give the same logic. We conclude with some discussions about notions of deontic non-contingency and deontic contingency.