 which is just \(\neg \OB p \amp \OB p\) in disguise (given \(\OB\)-RE and the Traditional Definitional Scheme). So (1′), given NC, yields a contradiction. Another way to put this is that the “can” of permissibility seems to be the dual of “must” not the dual of “ought”. This yields a dilemma: either deontic necessity represents “ought”, in which case, its dual does not represent permissibility (and neither does any other construction in SDL), or permissibility is represented, but “ought” is inexpressible, despite the ubiquitous assumption otherwise. That “ought” is the dual of permissibility is really a largely overlooked dubious yet pervasive bipartisan presupposition in both ethical theory and deontic  logic.[58]