is it possible to call "have to", need to", "be able to" and "be used to" a SEMI-MODAL?

Many sources call them 'semi-modals', Seyfihoca, though they may be grouped in various ways.

“Have to ... though semantically very close to must, has none of the modal properties and is clearly a catenative [verbs with verbal complements, like want to], not a modal.” (Huddleston, 1984: 165) But for others, such as Palmer, the meanings of have to and other forms including to be going to, to be able to, and would rather make them “semi-modals” (Palmer, 1990: 25).

The question of which syntactic role these semi-modals have in a sentence is problematic. Are the semi-modals auxiliaries or main verbs? Palmer does not directly address the question, but in a discussion on be bound to, he does make reference to the main verb being a verb of action, suggesting that he sees be bound to as an auxiliary (Palmer, 1990). Celce-Murcia & Larsen-Freeman (1983: 83) note that periphrastic modals (the semi-modals ending with to) “behave syntactically more like main verbs than do modals”, but a footnote at the bottom of the same page seems to suggest that they still consider periphrastic modals to be auxiliaries. They also note that “Structurally, have to is not truly a periphrastic modal since it requires do support .... In other words, have to looks like a verb and behaves very much like a periphrastic form in many contexts. Thus we have treated it like one.” (1983: 81).

Many of the semi-modals behave oddly. Used to often takes do support (Did you use to live in New York?), while need sometimes acts as a proper modal auxiliary (you needn’t come) and sometimes as a semi-modal requiring do (you don’t need to come). Had better shows the formal characteristics of modal verbs (no -s, no non-finite form, no chaining with other modals), but the presence of better makes treating it as a modal verb problematic, to say the least.

It appears that the semi-modals are hybrid forms, combining characteristics of both main verbs and auxiliary verbs. It also appears that the category is defined by the semantic functions of its members, not their formal qualities. This is important because it suggests that there is no necessary main verb or auxiliary verb characteristic that all semi-modals must share. In other words, students need to calibrate the individual structural characteristics of the semi-modals since each semi-modal has its own combination of main verb and auxiliary verb characteristics. They also need to learn when and how to substitute semi-modals for modal auxiliaries, and to be aware for the subtle changes of meaning these substitutions sometimes indicate.
See p. 2 here:



The following verbs are often called "semi-modals" because they are
partly like modal helping verbs and partly like main verbs:

* need
* dare
* used to

Search this site (top right Search box) with:
need modal
dare modal
used to modal

and you'll find threads discussing them and examples, e.g.:

NEED ordinary verb/modal verb Any difference???
dare + verb infinitive form
Modal verb Used to, understood?

Students: Are you brave enough to let our tutors analyse your pronunciation?
One reference -- Paul Roberts' Understanding Grammar -- says need has become a sometimes modal auxiliary, while have to, be able to, and be used to are "equivalents of modal auxiliaries."
Need was not originally a modal auxiliary, but it has been drawn into the group because of its meaning, which has affinities with must, should, ought. It now fluctuates between the modal and the regular verb forms:

-He need only ask for what he wants.
-He needs only ask.
-He needs only to ask.

English has developed a number of verbs and verb phrases which, though they do not exhibit the formal characteristics of the modals, serve as auxiliaries to express similar colorings of meaning. Because there is no distinguishing form, the class cannot be delimited; similar locutions might be added to those given below, with the group blending gradually into the mass of verbal expression.

Be able to: This is used in preference to can and could where it is desired to represent the ability as a fact rather than a mere potentiality.

-He is able to support his mother.
-He was able to elude the posse.
-Can I play your cello? Yes if you are able to.

Have to: This very commonly substitutes for must. It is felt as a stronger, more literal expression of necessity:

-We have to consult Sidney.
-Did you have to do that?
-We have sometimes to spray the screens.
 Mister Micawber's reply was promoted to an answer.
i want some explanation and examples for the semi-modal verbs because i have a lesson about them and i hope that you are the best person who will help me ,please

and thank very much.
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 Marius Hancu's reply was promoted to an answer.