There is a small and rather special set of verbs called modal verbs. These are may, might, can, could, will, would, shall, should, must, ought, need, and a few others. The distributional test, that was described on pp. 36–7 above, shows that they are verbs because they can combine with a subject: They can sing He may arrive tomorrow I must have lost my presence of mind The children can sing James may arrive tomorrow Although these words are verbs, they have a much more restricted distribution than most verbs. For one thing, they are always followed by another verb. In the above examples can is followed by sing, may by arrive, and must by have (which, in its turn, is followed by lost). Modal verbs have a maximum of two forms; a base form and an irregular d-form. Might is the d-form of may; could is the d-form of can; would is the d-form of will; and should is the dform of shall. But must, ought and need have no d-forms; and none of the modal verbs have sforms or ing-forms (*mays, *musting, etc.). Modal verbs always come first in the verb phrase: may arrive, can sing, ought to have tried, etc. The verb ought is followed by the to-infinitive of the following verb, but this is exceptional; the other modal verbs are all followed by the base
form of the next word. Thus we can have might have but not might has or might had, and we can have can be but not can is or can was, etc. This is one of the places where the base form of be is used: He may be arriving tomorrow. All the categories of verb phrase that appear in Figure 13 can have a modal verb included in them but, of course, there are not so many variations because the modal verb does not have an s-form. The set of forms for modal verb
phrases is the subject of Exercise 7 (on p. 51).