Verbs are traditionally defined as words that “described an action or a state.” Auxiliary verbs are a subclass of verbs that add functional or grammatical meaning to the main verb. Auxiliary verbs differ from prototypical verbs in that auxiliary verbs perform a limited set of grammatical functions.
In grammar, a modal is a word that expresses 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. The auxiliary verbs that can function as modals include the modal verbs can, could, may, might, must, shall, should, will, and would and the quasi-modal verbs used to, ought to, had better (best), dare, and need. For example, the following italicized auxiliary verbs function as modals:
- Could you please pass the salt?
- He should study art professionally.
- Will you still love me tomorrow?
- I would be more careful if I were you.
- Grandma used to read me a story every night before bed.
- We dare not disturb the sleeping dragon.
Although prescriptive grammar rules proscribe against the use of more than one modal verb not linked by a coordinating conjunction within a single verb phrase, some Englishes do allow multiple modals. Both modal verbs within a multiple modal construction function as modals. For example:
- Could you may go?
- You think you might could tell me?
- You might should have told me that months ago.
- His life matches every definition of hero that you could can concoct.
- I used to couldn’t eat enough, and now I just eat because I feel hungry.
- I think it would will be bad for every people — everybody in the world.
Modal Verb as Modal
Quasi-modal Verb as Modal
Double Modal Verbs as Modals
Brinton, Laurel J. & Donna M. Brinton. 2010. The linguistic structure of Modern English, 2nd edn. Amsterdam: John Benjamins Publishing Company.
Hopper, Paul J. 1999. A short course in grammar. New York: W. W. Norton & Company.
Huddleston, Rodney. 1984. Introduction to the grammar of English. Cambridge: Cambridge University Press.
Kilby, David. 1984. Descriptive syntax and the English verb. Dover, New Hampshire: Croom Helm.
Leech, Geoffrey N. 2004. Meaning and the English verb. Harlow, English: Pearson Longman.