Modal verbs in modern english

CONCLUSION
Use must (present) and must have (past) when you are very certain that something is/was true.
Use can’t (present) and couldn’t have (past) when you are very certain that something is/was impossible.
Use should/shouldn’t (present) and should have / shouldn’t have (past) to talk about things you expect to be true, although you don’t have complete certainty.
You can also use should have / shouldn’t have for judging actions in the past to be good or bad.
Use might (most common), may, or could to talk about present and future possibilities.
Use might have, may have, or could have to talk about past possibilities
For a possibility that something did NOT happen, use might not have and may not have.
The modal verbs of English are a small class of auxiliary verbs used mostly to express modality (properties such as possibility, obligation, etc.).[1] They can be distinguished from other verbs by their defectiveness (they do not have participle or infinitive forms) and by their neutralization[2] (that they do not take the ending -(e)s in the third-person singular). The principal English modal verbs are can, could, may, might, must, shall, should, will and would. Certain other verbs are sometimes, but not always, classed as modals; these include ought, had better, and (in certain uses) dare and need. Verbs which share only some of the characteristics of the principal modals are sometimes called "quasi-modals," "semi-modals," or "pseudo-modals."
USED LITERATURE
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