  For example, consider a deontic logic, where \(\Box\) is read ‘it is obligatory that’. Here the truth of \(\Box A\) does not demand the truth of \(A\) in every possible world, but only in a subset of those worlds where people do what they ought. So we will want to introduce a relation \(R\) for this kind of logic as well, and use the truth clause \((K)\) to evaluate \(\Box A\) at a world. However, in this case, \(R\) is not earlier than. Instead \(wRw'\) holds just in case world \(w'\) is a morally acceptable variant of \(w\), i.e. a world that our actions can bring about which satisfies what is morally correct, or right, or just. Under such a reading, it should be clear that the relevant frames should obey seriality, the condition that requires that each possible world have a morally acceptable variant. The analysis of the properties desired for \(R\) makes it clear that a basic deontic logic can be formulated by adding the axiom \((D)\) and to \(\bK\).