Introducing Grades in Deontic Logics

Abstract

In this paper we define a framework to introduce gradedness in Deontic logics through the use of fuzzy modalities. By way of example, we instantiate the framework to Standard Deontic logic (SDL) formulas. Given a deontic formula Φ ∈ SDL, our language contains formulas of the form \(\overline{r} \to N\Phi\) or \(\overline{r} \to P\Phi\), where r ∈ [0, 1], expressing that the preference or probability degree respectively of a norm Φ is at least r. We present sound and complete axiomatisations for these logics.