Definition - A grammatical category that that deals with the expression of possibility, obligation, intention, and necessity.

Example -

(1) Sandy might be gay. (possibility)
(2) Sandy needs to be gay. (necessity)

Etymology -
The word derives from the Latin modus, measure or manner or mode.

Example Usages -

1. "In Kant's classification ‘the Categories of modality’ are those of possibility and impossibility, existence and non-existence, necessity and contingency; the term is coordinate with Quantity, Quality, and Relation."
(Source: OED s.v. modality )

2. "Modality: Whether a clause is a statement, question, negation, or imperative; another way of referring to some of the distinctions relevant to mood"
(Source: Pinker, Language Instinct, Glossary s.v. Modality )

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