 Very well-known modal logics are the normal modal logics that have a so-called possible worlds semantics making use of a two-place relation between possible worlds. Slightly less known are the classical (or congruential) modal logics (Segerberg 1971, Chellas 1980, Pacuit 2017). The weakest requirement imposed on a necessity-like modal operator \(\Box\) in systems of classical modal logic is the congruence property:  \[ \mathord{\vdash A \leftrightarrow B} \slashrel \mathord{\vdash \Box A \leftrightarrow \Box B}\]  (“if \(A \leftrightarrow B\) is provable, then so is \(\Box A \leftrightarrow \Box B\)”). This property, however, is certainly not distinctive of negation.