A modal verb is a type of verb that contextually indicates a modality such as a likelihood, ability, permission, request, capacity, suggestion, order, obligation, necessity, possibility or advice. Modal verbs generally accompany the base (infinitive) form of another verb having semantic content. In English, the modal verbs commonly used are can, could, may, might, shall, should, will, would, ought to, used to and dare.
Function
A modal verbs have a wide variety of communicative functions, but these functions can generally be related to a scale ranging from possibility ("may") to necessity ("must"), in terms of one of the following types of modality: epistemic modality, concerned with the theoretical possibility of propositions being true or not true (including likelihood and certainty) deontic modality, concerned with possibility and necessity in terms of freedom to act (including permission and duty) dynamic modality, which may be distinguished from deontic modality in that, with dynamic modality, the conditioning factors are internal – the subject's own ability or willingness to act
The following sentences illustrate epistemic and deontic uses of the English modal verb must: epistemic: You must be starving. ("I think it is almost a certainty that you are starving.") deontic: You must leave now. ("You are required to leave now.") An ambiguous case is You must speak Spanish. The primary meaning would be the deontic meaning ("You are required to speak Spanish.") but this may be intended epistemically ("It is surely the case that you speak Spanish"). Epistemic modals can be analyzed as raising verbs, while deontic modals can be analyzed as control verbs.
Epistemic usages of modals tend to develop from deontic usages. For example, the inferred certainty sense of English must developed after the strong obligation sense; the probabilistic sense of should developed after the weak obligation sense; and the possibility senses of may and can developed later than the permission or ability sense. Two typical sequences of evolution of modal meanings are: internal mental ability → internal ability → root possibility (internal or external ability) → permission and epistemic possibility obligation → probability
English
The following table lists modal verbs of standard English (some English modal auxiliary verbs, and some lexical verbs) and various senses in which they are used:
{ | class="wikitable" |- ! Modal verb !! Epistemic sense || Deontic sense || Dynamic sense
|-
| can || That can indeed hinder. || You can, if you are allowed. || She can really sing. |- | could || That could happen soon. || – || He could swim when he was young. |- | may || That may be a problem. || May I stay? || – |- | might || The weather might improve. || Might I help you? || – |- | must || It must be hot outside. || Sam must go to school. || – |- | shall || This shall not be viewed kindly. || You shall not pass. || – |- | should || That should be surprising. || You should stop that. || – |- | will || She will try to lie. || – || – |- | would || Nothing would accomplish that. || – || – |- |ought |That ought to be correct. |You ought to be kind. |– |- |need |– |I need to leave. |He needs to run fast to catch the bus. |- |have |That has to be Lee at the door. |I have to go. |– |- |require |– |You're required to leave. |– |- |oblige |– |You're obliged to come. |– |- |assume |I assume that's Lee. |– |– |- |manage |– |– |She managed to do it. |- |strive |– |– |I strive to be kind. |- |etc. |}
In other languages
Hawaiian Pidgin
Hawaiian Pidgin is a creole language most of whose vocabulary, but not grammar, is drawn from English. As is generally the case with creole languages, it is an isolating language and modality is typically indicated by the use of invariant pre-verbal auxiliaries. The invariance of the modal auxiliaries to person, number, and tense makes them analogous to modal auxiliaries in English. However, as in most creoles the main verbs are also invariant; the auxiliaries are distinguished by their use in combination with (followed by) a main verb.
There are various preverbal modal auxiliaries: Kaen "can", laik "want to", gata "have got to", haeftu "have to", baeta "had better", sapostu "am/is/are supposed to". Unlike in Germanic languages, tense markers are used, albeit infrequently, before modals: Gon kaen kam "is going to be able to come". Waz "was" can indicate past tense before the future/volitional marker gon and the modal sapostu: Ai waz gon lift weits "I was gonna lift weights"; Ai waz sapostu go "I was supposed to go".