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Concourse 2

Semi-modal auxiliary verbs and marginal modal auxiliary verbs


There is a general guide to modality and a guide to pure modal auxiliary verbs on this site.  This guide focuses only on semi-modal auxiliary verbs and what are called marginal modal auxiliary verbs or semi-modal auxiliary verbs (including the verb let).

In the following you will find reference to dynamic, deontic, alethic and epistemic modality.  If the terms are unfamiliar, you can safely ignore them but there is a link at the end to a guide in which they are explained.

Semi-modal auxiliary verbs

There is a certain amount of disagreement about what constitutes a semi-modal auxiliary verb.  For the purposes of this guide, we are considering verbs which can act both as modal auxiliary verbs and as 'ordinary' lexical verbs.
The three verbs which are most often defined as semi-modal auxiliary verbs are dare, need and used to.



Dare is an ancient word with connections to words pre-dating Old English.  It comes from a presumed Proto-Indo European root and occurs in Sanskrit, for example, as dadharsha.  It also has cognate forms in Old Norse, Old High German, Gothic, Old Persian, Ancient Greek etc.  In all these languages it had the meaning of to be bold.
An older English form had the irregular past tense durst which survived into the late 19th century but only occurs in some dialects today.
The verb still retains its meaning of have the courage to.
Consider these examples:

Modal auxiliary verb Lexical verb
  1. She daren't phone her mother
  2. She dared not phone her mother
  3. Dare she phone her mother?
  4. She wouldn't dare phone her mother
  5. I wonder if she dare phone her mother
  1. She doesn't dare (to) phone her mother
  2. She didn't dare (to) phone her mother
  3. Does she dare (to) phone her mother?
  4. She wouldn't dare (to) phone her mother
  5. I wonder if she dares (to) phone her mother

The contention here is that all these sentences are correct grammatically.  What conclusions can you draw?
Think for a little while and then click here.

To many, the modal forms of the verb sound slightly stilted and old fashioned and the non-modal, lexical forms are, in fact, more common as corpus research has shown.  The non-modal forms are also more common in American English.

In most cases, the verb expresses dynamic modality because it refers to the subject rather than to obligation imposed or likelihood imagined.  Other forms of modality occur in the three common set phrases with dare:

There is a transitive use of dare to mean challenge in expressions such as
    I dare you to jump
    He dared me to do it
    Did he dare you to do it?
etc.  In this use the verb is always a lexical verb, never modal.

Another, even rarer transitive use of the verb occurs in expressions such as:
    She dared the water
    I dared a question

where the meaning is something like have the courage to try.
Again, the verb is always lexical, never modal, in this meaning.



Need is the only semi-modal which fits into the notions of possibility, necessity etc. along with the central modal auxiliary verbs.
It does, however, have two non-modal, lexical uses.  Consider these examples:

Modal auxiliary verb Lexical verb 1 Lexical verb 2
deontic meaning deontic meaning requirement
  1. She needn't phone her mother
  2. Need she phone her mother?
  3. Needn't she phone her mother?
  1. She needs to phone her mother
  2. She doesn't need to phone her mother
  3. Does she need to phone her mother?
  4. Doesn't she need to phone her mother?
  1. I need a drink
  2. I don't need anything else
  3. Do you need anything?

What conclusions can you draw?
Think for a little while and then click here.

There is fruitful ground for confusion here, not least in the distinction between, for example:
She needn't have phoned her mother (but did)
She didn't need to phone her mother
(so didn't).

A further source of confusion is that the verb is usually used to refer to obligation, i.e., deontic modality, but it can be used to refer to logical necessity, i.e., alethic modality, as in, for example:
    A rectangle needs to have four sides
    How many sides does a rectangle need to have?
and in this case, it is always formed as a lexical verb.  However, in the negative, both
    A rectangle doesn't need to have four equal sides like a square
    A rectangle needn't have four equal sides like a square
are possible.
The negative is frequently formed with can't, as in:
    A square can't have more than four sides
and this implies prohibition rather than lack of obligation.

Again, to many, the modal form, especially the question, sounds formal and slightly stilted and again, the form is rarer in American English.


need as a face-saving device

There are times when need, must and have to may be used interchangeably but there are some important differences in nuance.
For example:
    You must buy a ticket
    You have to buy a ticket
    You need to buy a ticket

may be considered synonymous and, in many cases, they are.
All of these are examples of deontic modality and that is to do with obligation and duty.  So, for example,
    You have to fill in a form
    You must fill in a form
refer to the hearer’s duty and the obligation placed on him/her by the speaker.  It is sometimes used casually in spoken language to mean that this is not an obligation on you personally but a general truth.
However, in
    You need to fill in a form
The semi-modal need implies that it is a general rather than personal requirement, to do with the logical necessity of something being true.
This form is often used, for example, in the passive as:
    To be processed, the form needs to be submitted before the end of the month
which states a conditional necessity rather than a personal obligation.

The verb often implies some undesired consequence in the way that must and have to do not.  For example, choosing the formulation
    You need to be at the station by 6 (or you'll miss the train)
expresses the preference for avoiding the unwelcome consequence while
    You must be at the station by 6
expresses more direct obligation.

Face-saving for the hearer is often the motivation for selecting need over the more direct model verbs of obligation.  In, for example:
    Everyone needs to be in the office by 8 o'clock
no personal obligation is implied because this is simply company policy and not my imposition on you or anyone else.  It is more polite and distances the speaker from any sense of assumed authority.  If, on the other hand, I say:
    Everyone must be in the office by 8 o'clock
I am laying an obligation on each member of the group personally.
Compare, too, the use of need in, for example:
    The bank needs to have these figures tomorrow
    You have to / must give the bank the figures tomorrow
because the first saves the face of the hearer by not imposing authority on him/her.

Finally, we can ignore (if we wish) any statement using must or have to because we are independent operators.  So, for example:
    You have to come at 6 o’clock
is an obligation I can ignore if I choose and that might upset someone else, but
    You need to come at 6 o’clock
is probably not, because it implies that I will miss something important if I don’t, not that someone else will be upset.

used to

used to

The verb is used to talk about

There used to be (!) two forms with identical meanings, thus:

Modal auxiliary verb Lexical verb
  1. She used to live in Margate
  2. Used she to live in Margate?
  3. She usedn't to live in Margate
  4. Usedn't she to live in Margate?
  1. She used to live in Margate
  2. Did she use(d) to live in Margate?
  3. She didn't use(d) to live in Margate
  4. Didn't she use(d) to live in Margate?


  1. The modal forms are still encountered and should (perhaps) be taught for recognition purposes but the non-modal, lexical verb is now more common and, it seems fair to presume, will continue to grow in popularity.
    To many, the modal form is formal, stilted and even wrong.
  2. There is no requirement only to use the modal in non-assertive contexts.  This is unlike need and dare (see above).  So the verb maintains it form in questions, statements and negatives.
  3. There is some spelling confusing.  The 'd' is optional where shown in brackets, compulsory otherwise.
  4. Confusion with the be/get used to structures, as in, e.g.:
        I'm used to working late
    can mostly be avoided if you don't present them in the same lesson.
  5. The pronunciation of this verb to express habit varies from the verb meaning employ: the 's' is pronounced /s/ in the former and /z/ in the latter.  For example:
        I used a hammer (/ˈaɪ.ˈjuːzd.ə.ˈhæ.mə/)
        I used to work hard (/ˈaɪ.ˈjuːst.tə.ˈwɜːk.hɑːd/)
  6. Used to can be replaced by would usually after used to has set the scene.  For example:
        We used to take our holidays in Margate where we would stay in a guesthouse and would go swimming every day ... .
    However, only used to may refer to past states rather than actions:
        He used to be so slim
        *He would be so slim
    (There are exceptions to this classroom rule when it comes to the use of copular verbs.
    Would can be used with verbs which convey the relationship between subject and complement like be, appear, seem, remain etc. in, e.g.
        She would sometimes be a difficult person to talk to
        He would often appear uninterested
        I would remain in the house
    Frequently, we insert time adverbials in these formulations.)

half moon

Semi-auxiliaries or Marginal modal auxiliary verbs

Apart from pure and semi-modal auxiliary verbs, there is a class of multi-word verbs which are often referred to as semi-auxiliaries (and just as often dumped into the semi-modal category).  They are also called marginal modal auxiliary verbs because they are often lexical equivalents of true modal auxiliary verbs.
What you call them is of little consequence but their behaviour requires special treatment in the classroom because they, too, act like modal auxiliary verbs insofar as they:

They all, however, make questions and negatives as main verbs do and cannot be inverted for questions or negated without an auxiliary (do).
They also all, where it is appropriate, take a third-person, singular -s or -es inflexion as well as conventional past-tense markers and aspectual features.

A short list includes:

happen to
As in, e.g.,
    I happened to see John yesterday.
The sense is
    By chance I saw John
rather than by arrangement or plan.
care to
This is similar in sense to would like to but can only be used non-assertively so we can have:
    Do you care to go out?
    I don't care to eat in smoky restaurants

but not
    *I care to eat out
mean to
This semi-auxiliary is often used for intentions in the same way that going to is used as in, e.g.,
    I mean to call on him on my way.
(The verb mean followed by a -ing form is not in this category.  That verb signifies that something is involved or implied as in:
    I need a new car but that means spending money I don't have.)
seem to
This verb has no modal equivalent and is often classified (wrongly) as a copula.  It is a copular verb when it is used without another verb as in, for example:
    He seems happy
The sense of seem to is different and is usually one of doubt or uncertainty so it belongs with the pure modal auxiliaries such as might, may, could etc. as in, e.g.,
    He seems to be unhappy
It expresses epistemic modality because it concerns the speaker's view of the likelihood of a proposition being true.
tend to
In the present tense this verb suggests preference (and, therefore, habit) as in, e.g.,
    I tend only to watch the news on TV.
In the past, however, it often performs the same function as the semi-modal used to as in, e.g.,
    We tended to take long walks on our holidays
    We used to take long walks on our holidays
    We would take long walks on our holidays.
turn out to
This is often not classified as a semi-auxiliary, and it is not one in something like:
    The weather turned out nice
where it is a copular phrasal verb, linking the subject and the epithet.
However, it has affinities with auxiliaries in expressions such as:
    He turned out to want even more money
be about to
This semi-auxiliary is also often used as an equivalent to going to but emphasises the close proximity of the events in time.
Both are used in the past to refer to a frustrated plan.
Compare, e.g.,
    I was about to have dinner when you called
    I was going to have dinner when you called.
Both are used in the present to refer to a future based on current evidence or previous experience (and so are epistemic in sense).  E.g.
    Look at the weather.  It's about to rain / It's going to rain
    Don't argue any more; she's about to / going to lose her temper.
be likely to
This is modal in nature and clearly expresses a degree of probability so belongs with central or pure modal auxiliary verbs like may, could, will etc. and concerns epistemic modality.  Compare, e.g.,
    He's likely to be late
    He may well be late
be supposed to
This has affinities with modal auxiliaries such as should, ought to and must (in some senses) and refers to obligation (deontic modality) and to likelihood (epistemic modality).
Compare, for example,
    You aren't supposed to be in here
    You shouldn't be in here
which are both deontic in meaning, referring to obligation or duty, with
    The train ought to be here at 6
    The train is supposed to be here at 6.
which are both epistemic, referring to the speaker's perception of the truth of a proposition.
There is sometimes a sense with this construction that the event or state has not taken / will not take place although it should.  Compare, e.g.:
    He's supposed to be here already (but he isn't)
    He should be here already (and I think he is)
    I should go (and probably will)
    I'm supposed to go (but probably won't)

teaching semi-auxiliaries

If the teaching of modality starts (as it very arguably should) with meaning and speaker perception, then integrating the semi-auxiliaries into lessons focused on notions such as probability, permission, prohibition, futurity, intention and so on is quite straightforward.
The forms are easy enough to teach and the usefulness of the verbs is often overlooked, especially as some have no clear modal-verb equivalents but still refer to the speaker's perception of events and states.



This verb is somewhat anomalous, quirky, even, and many analyses will not consider it a modal auxiliary verb of any type.  Here it follows the section on marginal modal auxiliary verbs but could just as easily be inserted after the semi-modal auxiliary verbs proper.  It shares some modal characteristics as well as functioning as a causative or main verb in, e.g.:
    I let my students leave early (causative)
    They didn't let me finish
    Do they let dogs in here?
(main, transitive verb)
There is a guide to the causative on this site.

When it takes on its modal clothes, the verb is used to oblige, make suggestions and make offers (deontic modality again) and it works like this:

Offer / Obligation / Permission Suggestion
deontic modality cohortative meaning
  1. Let me help you
  2. Let him help
  3. Did she let you help?
  4. Did they let you come in?
  5. She doesn't let me help
  6. The boss lets me go early
  1. Let's go to Margate
  2. Let's not go to Margate
  3. Don't let's go to Margate

In the functions of offering, permission and obligation, the verb has no modal characteristics (it has a past form [irregular and unchanged], takes a third-person -s and forms questions and negatives with the do operator).  The form is usually one of a simple imperative and can be softened with please etc.

The verb works as a modal auxiliary, however, insofar as it cannot appear without a main verb and implies suggestion, obligation and so on.  In this regard, it acts often as a cohortative expression, inviting cooperation rather than expressing obligation (7, 8 and 9, above).

(Incomplete) Summary


Related guides
the essentials of modality a simpler guide in the initial training section
pure modal auxiliary verbs taking each pure modal in turn and identifying its function
modality: tense and aspect which considers modal auxiliary verbs and perfect and progressive forms
complex tenses which also considers complex tenses in relation to modality
teaching modality for some more ideas transferable to the analysis above
types of modality for more on types of modality such as epistemic and deontic modality
copular verbs for a little more on how seem and turn out can be used
assertion and non-assertion for a little more on the differences between these ideas
suasion for more on hortation and optative meanings