Modals in English grammar are words that express modality. Modality is the grammaticalized expression of the subjective attitudes and opinions of the speaker including possibility, probability, necessity, obligation, permissibility, ability, desire, and contingency.
Modal is a grammatical function.
The grammatical form that can function as the modal in English grammar is the verb phrase. The nine auxiliary verbs, or modal verbs, that can function as the modal are the verbs can, could, may, might, must, shall, should, will, and would. The five quasi-modal verbs that function as modals are ought (to), had better (had best), used to, dare, and need.
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