Modal Logic

A family of formal logics that extend propositional or predicate calculi with modal operators (such as □ for necessity and ◇ for possibility) to express modes of truth relative to points in a model equipped with an accessibility relation.

A family of formal systems that extend classical propositional or predicate logic by introducing modal operators (commonly read as necessity □ and possibility ◇) and specifying their syntax, axioms and semantics—typically via relational (possible‑world) models or other frame structures—to analyze modal notions such as necessity, possibility, obligation, knowledge and temporal modalities.