Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

CORE MODAL VERBS

380

General formal properties of modal verbs

380a

The forms of modal verbs differ from the forms of other types of verb in significant

ways. Modal verbs have only one form and do not inflect for person or number.

Modal verbs do not have infinitive forms, either with to or without. Modal

verbs have no -ing form and no -ed participle form and therefore lack progressive

and perfect forms:

I’d like to be able to speak Japanese.

(I’d like to can speak Japanese.)

Modal verbs are placed first in the verb phrase and are followed by a verb in the

base form. The next verb may be a lexical verb or an auxiliary verb (be, do, have)

or the substitute verb do, but cannot be another modal verb:

We 

might stay an extra night.

We 

should be leaving soon.