Modality (Grammar and Semantics)

In grammar and semantics, modality refers to linguistic devices that indicate the degree to which an observation is possible, probable, likely, certain, permitted, or prohibited. In English, these notions are commonly (though not exclusively) expressed by modal auxiliaries, such as can, might, should, and will. They are sometimes combined with not.

Martin J. Endley suggests that "the simplest way to explain modality is to say that it has to do with the stance the speaker adopts toward some situation expressed in an utterance...[M]odality reflects the speaker's attitude toward the situation being described" ("Linguistic Perspectives on English Grammar," 2010).

Deborah Cameron illustrates with an example:

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Modal Verbs in English

By Richard Nordquist

"[Modality] is what makes the difference between a factual assertion like unicorns never existed, and a more guarded view, such as it seems unlikely that unicorns could ever have existed—or a bolder claim like the existence of unicorns must always have been a myth. Modality, then, is a resource speakers and writers use when they are staking claims to knowledge: it allows them to formulate different kinds of claims (e.g., assertions, opinions, hypotheses, speculations) and indicate how committed they are to those claims." ("The Teacher's Guide to Grammar," Oxford University Press, 2007)

Indicating Modality Grammatically

Just as tense indicates a time aspect of a verb, words that are used to show modality indicate the mood of the sentence—that is, how factual or assertive the statement is—and it can be done in any number of ways, including with adjectives. Martin J. Endley in "Linguistic Perspectives on English Grammar" explains:

"Thus, a situation might be described as possible, probable, necessary, or certain. The noun counterparts of these adjectives also express modality so that a situation can be described as a possibility, a probability, a necessity, or a certainty. Moreover, it is possible to use ordinary lexical verbs to convey modality....And think about the difference between saying that you know something and saying that you believe something. Such differences are essentially a matter of modality. Finally, English also contains certain semi-fixed lexical phrases (e.g., rumor has it) that are, basically, modal expressions." (IAP, 2010)

Other terms that express modality are marginal modals, such as need, ought to, dare, or used to.

In Depth: Types of Modality

The range of possibilities expressed when using modality is a broad spectrum, ranging from not very likely to very likely; to express these different levels, modality comes with named gradations, as explained by authors Günter Radden and René Dirven, in "Cognitive English Grammar": 

"Modality is concerned with the speaker's assessment of, or attitude towards, the potentiality of a state of affairs. Modality, therefore, relates to different worlds. Assessments of potentiality, as in You must be right, relate to the world of knowledge and reasoning. This type of modality is known as epistemic modality. Modal attitudes apply to the world of things and social interaction. This type of modality is known as root modality. Root modality comprises three subtypes: deontic modality, intrinsic modality and disposition modality. Deontic modality is concerned with the speaker's directive attitude towards an action to be carried out, as in the obligation You must go now. Intrinsic modality is concerned with potentialities arising from intrinsic qualities of a thing or circumstances, as in The meeting can be canceled, i.e. 'it is possible for the meeting to be canceled.' Disposition modality is concerned with a thing's or a person's intrinsic potential of being actualised; in particular abilities. Thus, when you have the ability to play the guitar you will potentially do so....Modal verbs have a special status among modal expressions: they ground a situation in potential reality." (John Benjamins, 2007)