  The most general way to formulate quantified modal logic is to create \(\mathbf{FS}\) by adding the rules of \(\mathbf{FL}\) to a given propositional modal logic \(\mathbf{S}\). In situations where classical quantification is desired, one may simply add \(Et\) as an axiom to \(\mathbf{FS}\), so that the classical principles become derivable rules. Adequacy results for such systems can be obtained for most choices of the modal logic \(\mathbf{S}\), but there are exceptions. 