English modal auxiliary verbs
Class of auxiliary verbs in English that lack untensed forms / From Wikipedia, the free encyclopedia
The English modal auxiliary verbs are a subset of the English auxiliary verbs used mostly to express modality (properties such as possibility and obligation).[lower-alpha 1] They can most easily be distinguished from other verbs by their defectiveness (they do not have participles or plain forms[lower-alpha 2]) and by their lack of the ending ‑(e)s for the third-person singular.[3]
The central English modal auxiliary verbs are can (with could), may (with might), shall (with should), will (with would), and must. A few other verbs are usually also classed as modals: ought, and (in certain uses) dare, and need. Use (/jus/, rhyming with "loose") is sometimes classed so as well. Other expressions, notably had better, share some of their characteristics.