Words like “will,” “would,” “must,” “may,” “might,” “can,” and “could” are modal auxiliaries, or “modal auxiliary verbs.” Sometimes they are called simply “modals” or “modal verbs.” In all of English there are only twelve modal auxiliaries, and two of them—“need” and “dare”–are only rarely used nowadays as modals. Wordsmyth recognizes the following as words that can function as modal auxiliaries.
| can | could | dare | may | might | must | need |
| ought | shall | should | will | would |
Modals are used before other verbs (main verbs) and add particular types of meaning to those verbs. If we say “She can swim”—where “swim” is the “main verb”–the modal “can” adds the meaning of ability to the idea of swimming. In other words, “She can swim” is the equivalent of “She has the ability to swim.” Some of the other meanings that modals give are the notions of possibility, willingness, futurity, necessity, obligation, advisability, and permission.
Modal auxiliaries are unique because they act like verbs in some very important ways, but they do not act like verbs in all the ways that would qualify them as true verbs in modern English. Modals take the same place in a sentence as regular verbs, but they don’t change their form to agree with their subject—there is no *“he woulds” or *“she mights,” for example. Similarly, there are no special past tense forms—no *”coulded” or *“musted.” (Historically, however, the forms “might,” “would,” “could”, and “should” are themselves past tense forms. In modern English, these modals function in unique ways and often are used to refer to future time, as in “He might come to the party tomorrow.”) While modals differ from regular verbs, they can be used negatively with “not” like the ordinary auxiliary verbs “do, “be,” and “have” (“I do not believe it,” “I could not believe it”), and they function in a similar way to “do,” “be,” and “have” in questions (“Do you?” “Are you?” “Can you?” “Has he?” “Will he?”)
The modals “dare” and “need” function much more often as ordinary verbs than as modal auxiliaries. In fact, as modals, they are rarely used in modern American English other than in a few set expressions. As modals, they make their question form and negative forms the same way as other modals: “Need I remind you of that fact?” “You needn’t answer that question,” “I dare not ask him,” “Dare I say it?” These modals are even more unusual, though, in that they rarely, if ever, occur in non-questions or non-negatives.