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Concourse 2

Multiple modalities

3

One of the defining characteristics of central modal auxiliary verbs is that, in standard varieties of English, the verbs cannot co-occur.  We do not, therefore, allow:
    *She can must do it
    *John could might allow it
    *The president can't may have the answer

and so on.
This means that when we use central modal verbs to express various types of modality we are confined, in standard varieties of English, to one form of modality at a time.  So, for example, if we want to express a range of permissibility, from obligatory to forbidden (deontic modality), we can do so using modal auxiliary verbs and we can also express degrees of likelihood (epistemic modality) and willingness or ability (dynamic modality) in the same way.  However, we cannot combine deontic, dynamic and epistemic modality through the use of central modal auxiliary verbs.  We only allow, therefore, for example:

  1. Deontic modality (degrees of permissibility)
        You must fill in this form
        She should get herself a new laptop
        You can't go yet

    etc.
  2. Epistemic modality (degrees of likelihood)
        That must be her brother
        She should be here soon if she caught the right train
        I may be a bit late tomorrow because I I'm going for a drink

    etc.
  3. Dynamic modality (degrees of willingness and ability)
        I can help with that
        She won't help
        He could speak French when he was a child

    etc.

and, as we saw above, no combination of different sorts of modality can be achieved with any central modal auxiliary verbs.  On this site, those verbs are identified as:
    can | could | may | might | must | shall | should | will | would | ought
and we also included had better because it acts in a similar way.
In the guide to central modal auxiliary verbs (linked below), incidentally, the analysis identified nine other defining characteristics but they do not concern us here.

There is a fourth form of modality which refers to the inevitable truth of a proposition because of the way the universe works, alethic modality, but, because the reference is to a universal, context-independent truth, it is not combined with other forms of modality.  We cannot allow, therefore,
    *A rectangle could have to have four sides
because it makes no sense.

If the terms deontic, epistemic and dynamic modality are obscure to you, you could follow the general guide to types of modality, linked below.  What is said above, however, is enough for the purposes of this guide.

We have been careful to note that we are talking about standard varieties of English in terms of the non-co-occurrence of central modal auxiliary verbs.  In many dialects of the language, not least Southern USA usage, central modal auxiliary verbs often co-occur so we may encounter, for example:
    He should ought to be here
and so on.

In very casual speech, too, it is often observable that speakers of English are searching for a way to combine modalities so it is not impossible to encounter something like:
    Of course, if the boss demands it, I might must be there
but this is non-standard and unlikely to be encountered in writing or more careful speech.


talk

Communicative need

There are times when we need to combine types of modality to make our point clear so it is possible that we want to express something like:
    There is a possibility that he will want to have the ability to change the ticket
but we cannot express the thought using central modal auxiliary verbs because:
    *He may will can change the ticket
is obviously not allowed.
This restriction does not apply universally across languages, in fact, and many do allow multiple uses of equivalent verbs in single clauses.  For example, the forbidden
    *He must can come
in English, can be translated as:
    Han måste kunna komma (in Swedish)
    Er muss kommen können (in German)
    Il doit pouvoir venir (in French)
    Debe poder venir (in Spanish)
    Musí být schopen přijít (in Czech)
and so on and in all these cases there is a co-occurrence of modal auxiliary verbs.
Learners from language backgrounds that allow the co-occurrence of modal auxiliary verbs may be confused and frustrated by the irregular nature of what is and is not allowed in English.  That, of course, is a source of error because the temptation will often be to translate directly.


maze

The workarounds

All human languages are capable of expressing all human thoughts so it is not surprising that English can express combinations of types of modality perfectly adequately.
How it does that is a confusing mishmash of forms, however, and the root of much difficulty for learners at all levels.

combination

Combination 1: epistemic and deontic

We can combine expressions of likelihood and permissibility in these ways, the first two of which are the generally preferred routes and should be taught first.  English happens to have a non-defective form for obligation (have to, don't have to, haven't to) so the following are possibilities:

  1. Central modal auxiliary verb plus semi- or marginal-modal auxiliary verb
    For example:
        John might be let go
        I may be needed to work tonight
        I might be supposed to do the work
        It may need to be done
        They might have to get a new one
        She could have had to take a bus
  2. Central modal auxiliary verb plus a lexical or main verb
    For example:
        John must be forced to do it
        They might be told to come
        They could be allowed to leave early
        I doubt she may be allowed in
  3. Central modal auxiliary verb plus modal noun
        That could be an obligation
        She might have that duty
        It's a possibility I must be there
  4. Central modal auxiliary verb plus a modal adverb or adjective
    For example:
        It's inevitable she must earn more
        It might be compulsory
        That could be permissible
        That might be obligatorily done
bird cat

Combination 2: epistemic and dynamic

Because English also happens to have a simple modal adjective form connected to its subject by the copula or a pseudo-copula: able to, become unable to etc.  The combination is also describable as a marginal modal form and is so identified in the guide to semi- and marginal modal auxiliary verbs.  It is often used to combine the types of modality like this:

  1. Central modal auxiliary verb plus semi- or marginal-modal auxiliary verb
    For example:
        John should be able to do it in time
        I may be unable to help tonight
        I might not be able to understand him
        They might not have been able to get a seat
    An alternative analysis here is that the structure is simpler: a modal auxiliary verb plus a predicative adjective, able / unable.
  2. Central modal auxiliary verb plus a lexical or main verb
    For example:
        John might succeed in doing that
        That may work well
        They could manage the issue
        I can imagine that she intended to go
  3. Central modal auxiliary verb plus modal noun
        That could be a success
        She may have had some ability
        It's a certainty that Mary can help
        She might have shown some willingness
  4. Central modal auxiliary verb plus a modal adverb or adjective
    For example:
        She must be capable of doing the work this week
        It might be doable
        That could be possible
        John could be willing to see her
        That might be successfully done
combine

Combination 3: deontic and dynamic

It is here that a good deal of ambiguity arises in English because the modal auxiliary verbs used to express deontic modality (permissibility) and epistemic modality (likelihood) are often the same so, for example:
    I could have left my keys with John
means either:
    I might have left my keys with John (epistemic modality referring to a possibility)
or
    I was allowed to leave my keys with John (deontic modality referring to permission)
The combinations are possible, of course, but we need some co-text and context to disambiguate the forms.

  1. Central modal auxiliary verb plus semi- or marginal-modal auxiliary verb (or the adjective (un)able)
    For example:
        John should be able to do it in time
        They must be able to help tonight
        I had better be able to explain it
        They won't have been able to get one
  2. Central modal auxiliary verb plus a lexical or main verb
    For example:
        John must get it done
        She must succeed
        They ought to manage the issue
        I can't do it
    again
  3. Central modal auxiliary verb plus modal noun
        She should have some success
        She ought to have had more ability
        It's a certainty that Mary can help
        She may show some willingness
  4. Central modal auxiliary verb plus a modal adverb or adjective
    For example:
        She must be capable of doing the work this week
        It must be doable
        That could have been possible
        John should be able to do it
        That ought to be carefully done

half

Semi-modal auxiliary verbs

We see above that semi-modal auxiliary forms are frequently combined with other semi- and central modal auxiliary verbs to make meanings which combine two types of modality.  On this site, semi-modal auxiliary verbs are identified as dare, need, have (to) and used (to).  To that list, for our purposes here, we can add be able (to) because it, too, can function in multiple modal utterances.

These semi-modal verbs are often used to combine modalities as in, e.g.:


marginal

Marginal modal auxiliary verbs

There are a few marginal verbs which can combine with other forms to produce multiple modal meanings.  Examples include:


teacher

Teaching multiple modalities

Combining types of modality is, as we see above, not a simple matter in English and we also noted above that other languages are far more forgiving than English in this respect.  The fact that English does not permit the co-occurrence of a range of central and other modal auxiliary verbs causes some difficulty because learners from many language backgrounds can see no logical reason why:
    *He had to could be there
is not allowed.
This is, therefore, not an area with which we need to trouble lower-level learners but it is one which needs tackling at higher levels where more sophistication is needed.

Comprehension is always a good beginning in this area because learners may not notice that some sentences contain multiple modal meanings unless their attention is explicitly drawn to the phenomena.  Here's one way of doing that:

Draw lines to connect the meanings on the left with the meanings on the right.
She must
She can
  She ought to be willing to help
She should
She will
They may be able to help
I will
I should
She has to be able to help
They may
The can
I should be willing to help

and so on.

We can start from more simple forms and work our way up.  For example:

In English, the forms of the left are all wrong (but they may be possible in your language).
How can you rephrase them in correct English and keep the same sense?
The first one is an example.
He must can leave soon He must be able to leave soon
She should can go  
They may can't do it  
The had to could help  

and so on.

When we get really sophisticated, we can begin to introduce some of the less common and more formal ways to combine modality using other, non-modal auxiliary verbs.  As in, e.g.:

Rephrase the sentences on the left using modal auxiliary verbs where possible.
The first one is an example.
She is obliged to learn to do this She must become able to do this
It is possible they might be allowed to go home  
It is unlikely she has the strength to lift it  
It is probable that he is obliged to be late  

Now try doing this the other way around.

Rephrase the sentences on the left using modal nouns, adjectives and adverbs but not modal auxiliary verbs.
The first one is an example.
She must become able to do this She is obliged to learn to do this
We might be able to ask questions at the end  
They can't have to leave yet, can they?  
She used to have to be at work at seven  

and so on.

Communicatively, the area is more challenging but some kind of simulated communicative events can be set up for freer practice such as, e.g.:

Many other scenarios are possible of course.



Related guides
central modal auxiliary verbs for the guide to these non-co-occurring verbs
semi-modal auxiliary verbs in guide which also considers marginal modal auxiliary verbs such as seem, tend, be about to etc.
types of modality for the guide to types of modality such as epistemic and deontic modality
modal auxiliary verbs: tense and aspect a guide which considers the modal auxiliary verbs in relation to perfect and progressive forms
complex tenses a guide which considers complex tenses in relation to modality (I shouldn't have done it etc.)
teaching modality for some ideas
the modality index for links to a range of related guides