Modal auxiliaries: How to define? How to teach?



Modal auxiliaries are a problem for my students. I'm not sure that have to, be supposed to and need to are really modals since they change form to agree with their subjects. What should I think?

A teacher in Boston


Some terms grammarians use for expressions such as have to and need to are: "near modals," "quasi-modals," "semi-modals," or "marginal modals," which all show how close in meaning they are to the true modals.

It's logical and helpful to teach these near-modals together with the true modals. It makes the meaning of the true modals quite clear. In fact, in some cases, learners need to know the forms the near-modals right along with those of the “true modals.” An example of this is have to, which really has to be/ must be learned at the same time as must. See Marilyn's reasoning (just below).



Have to is one of the most useful verbs in the English language and should be taught early, as a main verb. It resurfaces in an important role when the modal must is taught. Whereas must, in its meaning of strong obligation, occurs in affirmative statements, the negative and interrogative forms require have to, as in (b) and (c) below:

(a) Passengers must show ID when boarding the plane

(b) Do passengers have to show their ticket receipts when boarding the plane?

(c) Passengers do not have to show their ticket receipts when boarding the plane.

Furthermore, since must is not generally used in independent clauses in the past, (but it is used in subordinate clauses), learners need to know that it's necessary to use had to. Compare (d) below, a statement about the present and future, and (e), a statement about the past:

(d) When a player's contract is up, he must receive a new offer that equals the old.

(e) Under the old arrangement, when a player's contract was up, he had to receive a new offer that equaled the old.

(adapted from the online Collins COBUILD Concordance Sampler)

Have to combines freely with the “true” modals, as in “You'll have to take a later flight “or “He shouldn't have to choose his major so soon.” Therefore, and also because it is such a useful and necessary verb to know for communication, have to is an important verb for learners to know early. At a more advanced stage, they can profitably learn have got to.

Need to can and should be taught as a main verb, not a kind of modal. Need to has all the features of the main verb need, including marking for person and tense, as well as do-support for negatives and questions. It also carries lexical meaning: there is no difference in meaning between the two needs in “I need a vacation” and “I need to take a vacation.” Or between “Your hair needs cutting” and “Your hair needs to be cut.

The “true” modal need, followed by the bare infinitive, e.g., You need look no further, is restricted to hyperformal style and occurs almost exclusively in negative statements. It is therefore of little use to lower-level learners. It can be taught to advanced learners who will be reading texts in which it can be expected to occur.

I should point out that need to does have a pragmatic, or practical, relation to should and ought to. In face-to-face interactions, need to is often a less threatening way to give advice or directives. Compare:

(f) You should use a finer grade of sandpaper on that fender

(g) You ought to use a finer grade of sandpaper on that fender

(h) You need to use a finer grade of sandpaper on that fender

The use of need to in (h) is less authoritarian than should in (f) or ought to in (g), and would be useful for ESL learners who are actually going to interact with native speakers and who might be perceived as too aggressive if they use should or ought to. Usually this kind of information in EFL (as opposed to ESL) courses can be deferred to the advanced level.

Be supposed to has several meanings—mild obligation and expectation among them. In this respect it resembles should and ought to. It does not, however, share any of the grammatical features of modals, and does not figure in any of the permutations of modals, as does have to.

Be supposed to is a member of a rather large group of verbs known as semi-auxiliaries (not quasi-modals, near-modals, semi-modals, or marginal modals), including be able to, be about to, be going to, be likely to, and be willing to (from Quirk et al., A Comprehensive Grammar of the English Language, Longman, 1985). These verbs should be taught as needed. The resemblance in meaning between be supposed to and should/ought to (especially in the past) can be taught at a later stage.

Marilyn Martin