# Definitions for **modal logic**

### This page provides all possible meanings and translations of the word **modal logic**

### Princeton's WordNet

modal logic(noun)

the logical study of necessity and possibility

modal logic(noun)

a system of logic whose formal properties resemble certain moral and epistemological concepts

### Wiktionary

modal logic(Noun)

Any formal system that attempts to deal with modalities, such as possibility and necessity, but also obligation and permission.

### Freebase

Modal logic

Modal logic is a type of formal logic primarily developed in the 1960s that extends classical propositional and predicate logic to include operators expressing modality. 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. The traditional alethic modalities, or modalities of truth, include possibility, necessity, and impossibility. Other modalities that have been formalized in modal logic include temporal modalities, or modalities of time, deontic modalities, epistemic modalities, or modalities of knowledge and doxastic modalities, or modalities of belief. A formal modal logic represents modalities using modal operators. For example, "It might rain today" and "It is possible that rain will fall today" both contain the notion of possibility. In a modal logic this is represented as an operator, Possibly, attached to the sentence "It will rain today".

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"modal logic." *Definitions.net.* STANDS4 LLC, 2014. Web. 20 Apr. 2014. <http://www.definitions.net/definition/modal logic>.