  Deontic logics introduce the primitive symbol \(O\) for ‘it is obligatory that’, from which symbols \(P\) for ‘it is permitted that’ and \(F\) for ‘it is forbidden that’ are defined: \(PA = {\sim}O{\sim}A\) and \(FA = O{\sim}A\). The deontic analog of the modal axiom \((M): OA\rightarrow A\) is clearly not appropriate for deontic logic. (Unfortunately, what ought to be is not always the case.) However, a basic system \(\mathbf{D}\) of deontic logic can be constructed by adding the weaker axiom \((D)\) to \(\bK\).