Modal logic
From Wiki @ Karl Jones dot com
Modal logic is a type of formal logic primarily developed in the 1960s that extends classical propositional logic and predicate logic to include operators expressing modality.
Contents
Description
Modals -- words that express modalities -- qualify a statement.
For example, the statement "John is happy" might be qualified by saying that John is usually happy, in which case the term "usually" is functioning as a modal.
Traditional alethic modalities
The traditional alethic modalities, or modalities of truth, include:
- Possibility ("Possibly, p", "It is possible that p")
- Necessity ("Necessarily, p", "It is necessary that p")
- Impossibility ("Impossibly, p", "It is impossible that p").
Other modalities
Other modalities that have been formalized in modal logic include:
- Temporal modalities, or modalities of time (notably, "It was the case that p", "It has always been that p", "It will be that p", "It will always be that p")
- Deontic modalities (notably, "It is obligatory that p", and "It is permissible that p")
- Epistemic modalities, or modalities of knowledge ("It is known that p")
- Doxastic modalities, or modalities of belief ("It is believed that p")
See also
- Accessibility relation
- Counterpart theory
- David Kellogg Lewis
- De dicto and de re
- Description logic
- Doxastic logic
- Dynamic logic
- Enthymeme
- First-order logic
- Formal logic
- Frege–Church ontology
- Hybrid logic
- Interior algebra
- Interpretability logic
- Kripke semantics
- Logic
- Modal verb
- Multi-valued logic
- Possible worlds
- Predicate logic
- Provability logic
- Regular modal logic
- Relevance logic
- Research Materials: Max Planck Society Archive
- Rhetoric
- Statement (logic)
- Strict conditional
- Two dimensionalism
External links
- Modal logic @ Wikipedia