A Student's Introduction to English Grammar

§3.2 Modal auxiliaries 39

being reduced to couldn't, and so on. But in Present-day English they are best
regarded as inflectional forms, for two reasons.

Some of them are quite irregular. There is, for example, no general rule of con­

traction that would yield won 't from will + not: we simply have to note that

won 't is an irregular negative form, just as would is an irregular preterite form.

Similarly for can 't and shan't.

In subject-auxiliary inversion constructions they occur in positions where

verb + not would generally be impossible. We have, for example, Isn 't it ready?,

but not *ls not it ready?

3.2 Modal auxiliaries

There are two inflectional properties that distinguish the modal auxil­
iaries from all other verbs. They also share a purely syntactic property that distin­
guishes the prototypical ones from nearly all other verbs.

(a) Lack of secondary inflectional forms

Modals have only primary forms and hence simply cannot occur in constructions
requiring a secondary form - a plain form, gerund-participle or past participle. We
can see this clearly when we contrast the modal auxiliary must with have, which
can have a very similar meaning but is not a modal auxiliary:

[20] MODAL AUXILIARY NOT MODAL AUXILIARY

a. I must work late tonight. b. I have to work late tonight. [primary form]

11 a. *1 will must work late. b. I will have to work late. [plain form]

111 a. *1 am musting work late. b. I am having to work late. [gerund-participle]

iv a. * I've often must work late. b. I've often had to work late. [past participle]

(b) No distinct 3rd singular agreement form in the present tense

The modal auxiliaries show no agreement with the subject, having a single present
tense form. There are no special 3rd singular forms (cans, mays, musts, wills,
etc.). Note again, then, the contrasting behaviour of must and have:

[21] a. I must leave now.

11 a. She must leave now.

b. I have to leave now.

b. She has to leave now.

(c) Bare infinitival complement

[I st singUlar subject]

[3rd singular subject]

The prototypical modal auxiliaries take a single complement with the form of a
bare infinitival clause. Nearly all other verbs that select infinitival complements
take the to-infinitival kind: here again we can note the contrast between must and
have in [20-21]. There are some verbs that take bare infinitivals (one is help, as
in We helped wash up), but very few. There is also one verb that qualifies as a