Opacity and the Ought-to-Be

Abstract

In this regard, deontic logic would seem to be the nicest member of the modal logic family. This is how it should be. One expects no problems interpreting quantification into deontic contexts. Unlike the logics for alethic necessity or belief, with deontic logic there is not even a temptation to think that the values of the individual variables are intensions, or individual concepts, or possibilia (permissibilia ?). Statements of obligation, permission, prohibition, etc. seema to be directly about persons or things regardless of how they are conceived or described. The deontic operators thus certainly seem to be extensional; nevertheless, when principles of extensionality are assumed for standard systems of deontic logic, paradox appears.1