In
modal logic
Modal logic is a kind of logic used to represent statements about Modality (natural language), necessity and possibility. In philosophy and related fields
it is used as a tool for understanding concepts such as knowledge, obligation, and causality ...
, a regular modal logic is a modal logic containing (as axiom or theorem) the
duality of the modal operators:
and closed under the rule
Every
normal modal logic
In logic, a normal modal logic is a set ''L'' of modal formulas such that ''L'' contains:
* All propositional tautology (logic), tautologies;
* All instances of the Kripke_semantics, Kripke schema: \Box(A\to B)\to(\Box A\to\Box B)
and it is closed ...
is regular, and every regular modal logic is
classical.
References
*Chellas, Brian. ''Modal Logic: An Introduction''. Cambridge University Press, 1980.
Logic
Modal logic
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