FORMS OF MODAL VERBS
Modality covers a broad semantic area and can be expressed by many forms.
(a) In English, the core forms are the nine modal auxiliaries repeated here: can, could, may, might, will, shall, would, should, must. These are invariant forms which are followed by a bare infinitive; they negate with ‘not’ and invert with the subject in yes-no questions.
(b) The lexical-modal verbs or auxiliaries, composed of be or have + usually another element + infinitive (have to, have got to, be bound to, be supposed to, had better, be likely to etc.)
(c) There is also a cluster of semi-modal verbs: dare, need, ought. These verbs behave syntactically like modals (daren’t, needn’t, oughtn’t) as in 8 and 9. They are fairly rare and are mainly used in BrE. Dare and need are also used as full lexical verbs, as in 10 and 11. AmE favors the latter option. Ought is the only modal to be followed by a to-infinitive.
8 I daren’t say anything to her about the broken vase.
9 You needn’t wait.
10 Did he dare to ask you if you needed anything?
11 How much money do you need?
Other means of expressing modality are mainly lexical: they comprise modal adverbs, adjectives, nouns and verbs. These other modal elements tend to reinforce the core modals, as in ‘I’m sure she couldn’t possibly have said that’. This is sometimes called modal harmony and illustrates how modality can be expressed not simply at one point in an utterance by a modal auxiliary, but at different points right through the clause.
