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Concourse 2

Modality and modal auxiliary verbs: the essentials

modals

What follows refers only to English.  Languages deal with the modality in a bewildering variety of ways.


define

What is modality?

Modality differs from tense and aspect in that it does not refer directly to any characteristic of the event, but simply to the status of the proposition.
(Palmer, 2001:1)

In other words, modality concerns how the speaker / writer perceives a state of affairs.



confusing

Confusing modal verb terminology

Terminology in this area can get a bit confusing because authorities differ about the names we give to things.  Here's a short glossary:

  • modality
    refers generally to the way speakers express their view of an event in terms of possibility, probability, likelihood, certainty, permission or prohibition.  For example, I can say:
    Permission / Prohibition
        He must not do that
        He is not allowed to do that
        He is not supposed to do that
        That is forbidden him
        I forbade him to do that
    Possibility
        He might do that
        He isn't able to do that
    Probability / Likelihood
        He will do that
        I expect she'll be late
    Certainty
        That must be the right answer
        That's definitely wrong
    and these are all examples of modality in one form or another expressing the speaker's view of the status of the event.
  • modal verbs are often called modal auxiliaries and come in three flavours:
    • pure modals are the verbs
      could, might, may, should, would, must, can, will/shall, had better, ought to
      but even here you will find verbs included in or excluded from this list.  Some will call these central modal verbs.
    • semi-modal verbs are usually listed as
      need, have to, dare, used to
      although some will exclude have to from that list and some will include ought to and be able to in the list.  These are sometimes called marginal modals although on this site that term is reserved for the next group.
    • marginal modal verbs are verbs which express some form of modality but do not share the structural characteristics of pure or semi-modal verbs and there are lots of them including, e.g.:
      be supposed to, seem to, be likely to, be about to, tend to
      etc.
  • modal adverbials and adjectives are often included in the list because they, too, express similar concepts.  This area includes, for example
        it is important that
        it is vital that
        it is unlikely that
        it is necessary that
        necessarily
        importantly
        vitally
        crucially
    and a host more.  They are all ways of signalling the speaker's view of an event but do not use special verbs to do it.
  • modal nouns are also sometimes included in the list.  These are nouns often formed from modal adjectives and include, for example:
        there is a possibility that it will rain
        I am making the assumption that he's coming
        there's a strong probability that it will rain
    and so on.

unicorn

It might be a unicorn

As you can see from the above, modality needn't be expressed using modal verbs.  We can say, for example
    It seems unlikely to me that she has seen a unicorn
which expresses our view of the event.
We do use modal verbs for this kind of thing quite often, however, as in
    She can't have / mightn't have / couldn't have / must've / may've seen a unicorn.

See if you can match modal to function in this little test.


function

Function

It's not always as simple as it seems.  English uses modal verbs in a complicated way and the area causes endless problems for learners (and teachers).  For example, what do these sentences imply about the perceptions of the speaker?  Click here when you know.

  1. He may choose a book.
  2. He can open the door.
  3. He should be in London.

So, issue number 1 for teachers of English is always to provide a clear context for modal verbs.  If you don't do this, you will do more harm than good by confusing your learners.


form

Form

Here's a list of some modal verbs in English.  What's different about the semi-modal verbs?
Think about:

  • How we make a negative with all of these verbs.
  • How we make a question with all of these verbs.
  • Whether we put an -s ending on the third person singular of the verbs.
Pure modal verbs
can | could | may | might | shall | should | will |would | must | ought to
Semi-modal verbs
used to | need | dare

Click here when you've done that.


explained

Some common modal verbs explained

This is a short and partial overview of the functions of some of the common modal verbs.
For more, see the guide to modals one by one.

can / could

This verb can express:

  1. Ability:
        He can read Italian but can't speak it well
        He could play the piano well as a child
  2. Permission (present and future):
        Can I come in?
        No, you can't yet
        Could I talk to you tomorrow?
  3. (Im)possibility:
        Nobody can be sure
        The train could be late

may / might

This verb can express:

  1. Permission:
        You may ask a question now
        May I smoke here?
    (More rarely and more formally: Might I speak to you?)
  2. Possibility (present and future):
        We may arrive a little late
        He might come early

shall / should

Shall is arguably going out of fashion to express the future and there's a strong case to be made for not teaching it for that function, especially at lower levels.  However, there are other uses of shall which are still not always replaceable with will.  Only the third (and, possibly, the fourth) in this list are common these days and then only in British English.

  1. In questions:
        Shall I do my homework now?
  2. Insistence:
        You shall do what I tell you
  3. Intention:
        I shan't keep you long
  4. Suggestions:
        Shall we go?

Should is much more common and can express:

  1. Obligation:
        You should write to your mother more often
  2. Logical deduction:
        He should be there by now
  3. Advice:
        You should take something for that cough

What's the negative of the second example?  Right, it's something like
    He won't be there yet
or
    He can't be there yet.

will / would

  1. Willingness:
        I'll get the milk
        Will you have another?
    (The verb would can also express this sense in
        Would you like another?
    but can't be used to express personally willingness except in something like
        I'd like another
    or
        I would be happy to help.
    )
  2. Intentions and promises:
        I'll send you an email soon
        We won't keep you
        He told me he would write soon
        I thought he'd be quick
  3. Prediction (often based on past experience):
        It'll probably rain soon; it often does in November
        He knew it would rain
        He believed I would come
  4. Insistence (present and past):
        He will keep arguing with me
        He would keep changing the subject
  5. Probability:
        That will be him at the door now, That would be typical of him
  6. Characteristic behaviour / habit:
        We would often get up really early
        When I was younger, I would ...
    (Compare used to for this function)

must

  1. Obligation:
        You mustn't speak to me like that
        You must be home at 6
  2. Logical necessity / deduction:
        That must be his father; they are so alike
        There must be an error in the data

Negating these meanings is tricky.  What's the negative of the following?  When you have a brief note of the answers, click for comments.

  1. You must take the medicine every day.
  2. The figure must be correct.

ought to

  1. Obligation (weaker than must):
        She ought to ask if she doesn't know.
  2. Logical deduction / expectation:
        The bus ought to be here by now.

Note that the question and negative forms of ought, for example:
Ought I to come? (= Would it be best if I came)
She oughtn't to speak to me like that (= It is her duty to be more polite)
are somewhat rare and considered formal.
The forms are, however, parallel to all other pure modals and hence, the verb is considered here.


time

Time and tense

Only some modal verbs have obvious past-tense forms.  Here's a list.

Present Past
can could
may could / might
shall should
will would
must (had to)
---- used to
ought to ----
need ----
dare dared

There are two pasts of may: one for possibility, one for permission.  We can say
    I could ask questions
and
    I might ask questions
The first means
    I was able to ask questions
OR
    It is possible I'll ask questions
The second only means
It is possible that I will ask questions

and cannot be used for ability.
The past of must is often had to but not in all its meanings.


aspect

Aspect

Usually, when a modal verb's function is to express ability or permission, we can't use progressive or perfect aspects.  For other functions we can use these aspects.
(If any of the above confuses you, try doing the guide to tense and aspect and then coming back to review this page.)

For example:

Possibility

They may have got lost
They may have been driving too long
They can't / couldn't have got lost
They can't have been driving so long

Necessity

I must have left my keys on the table
She must have been working on a solution
You must be joking

Prediction

They will have driven that way
John will still be driving at midnight

This part of the page is available as a PDF document.  There is also a reference grid of the common modals.

Here's a pictorial (and incomplete) summary of the pure modals.  Your task is to look through it and make sure you can devise an example of all the functions.

all pure modals


Click here to do a short test.



Related guides
grid of the common modals for reference
PDF document a short PDF document covering some of the above
tense and aspect for some more information and the distinction
modality for the in-service guides to modality and modal verbs
modals one by one for a traditional guide to pure (or central) modal auxiliary verbs
semi-modal verbs the guide to semi- and marginal modal verbs


Reference:
Palmer, F. R, 2001, Mood and Modality, 2nd ed., Cambridge: Cambridge University Press