  Note that the characteristic axiom of modal logic, \((M): \Box A\rightarrow A\), is not acceptable for either \(H\) or \(G\), since \(A\) does not follow from ‘it always was the case that \(A\)’, nor from ‘it always will be the case that \(A\)’. However, it is acceptable in a closely related temporal logic where \(G\) is read ‘it is and always will be’, and \(H\) is read ‘it is and always was’.