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Concourse 2

Dynamic modality: expressing ability and willingness


The word dynamic derives from the Greek dynamikos meaning strong or powerful.  In English it has been defined as:

having a lot of ideas and enthusiasm; energetic and forceful
(Cambridge International Dictionary of English, 1995:434)

Linguistically, we need to be a bit more exact and define this form of modality as that which expresses ability or requirement of the subject to do something.  It is non-subjective insofar as it refers to fact rather than likelihood or obligation (which are expressed via epistemic and deontic modality respectively).

You may find dynamic modality referred to as personal modality because it refers to individuals and their ability or willingness to do something.  We don't use that term in this guide because dynamic modality may not, in fact, always refer to an individual, although it usually does, but it is an alternative.

Dynamic modality is one of the usual four categories of modality (the others being epistemic, deontic and alethic to which there are separate guides).
If these terms are mysterious to you, you should follow the guide to types of modality before tackling what follows.
There is, in fact, an argument that dynamic modality is not actually a form of modality at all because the speaker / writer is not:

  1. using a modal expression to express an opinion regarding the truthfulness or necessity of an event, state or action
  2. affecting the current situation by what is said

For example, with the modal auxiliary verb can, four clear types of modality can be expressed:

Example Type of modality expressed
You can go now Deontic: giving permission / removing the obligation to stay
It can't be a rectangle if it has five sides Alethic: expressing a factual state (also, arguably, not really a modal use at all)
That can't be the right answer Epistemic: expressing the speaker's view of the truth of a proposition
She can play the piano very well Dynamic: stating a simple fact about ability

Traditionally, following Palmer (2001) only the modal auxiliary verbs can/could and will/would express dynamic modality, i.e., express ability or willingness.
There are other ways to express the same notions, of course, and the grammar that is involved is not as straightforward as it might seem.
The following is an analysis which is focused on teaching the concepts and notions.


Expressing willingness

Both will and can are used to express the notion of willingness as in, for example:

  1. Jane will drive you to the station if you like
  2. Jane can drive you to the station if you like

Functionally, these two utterances are identical: they both express the subject's (Jane's) willingness to do something and do not express the speaker's view of any existing obligation or its lack or any comment concerning the truthfulness of a proposition.

There is, however, a difference in sense:
Sentence 1. concerns willingness alone but sentence 2. may be construed to suggest that not only is Jane willing to drive you to the station but that she is also able to do so (because, e.g., she has no other outstanding commitments).
The differences become clearer when set in a dialogue:

Fred: Jane will drive you to the station if you like Fred is stating that he understands that Jane is willing to do this
Jane: Sure, no problem Jane is confirming her willingness
Jane: Sorry, I won't drive in the dark Jane is stating her unwillingness
Fred: Jane can drive you to the station if you like Fred is stating that he understands that Jane is willing to do this
Jane: Sure, no problem Jane is confirming her willingness
Jane: Sorry, I've got to take the kids to school Now she is stating her inability rather than her unwillingness

The border between the notions of willingness and ability is blurred in English because we can express both functions with the same modal auxiliary, can/could, with no change to the intonation.
An example of this is a statement such as:
    I can help you with your homework
in which it is unclear (without a very explicit context) whether the speaker is stating an ability or a willingness to do something.  It can mean, therefore, either:
    I am able to help you with your homework
    I am willing to help you with your homework
The same ambiguity occurs with the interrogative forms:
    Can you help me with my homework?
    Could you help me with my homework?
in which the questioner may be referring to the hearer's ability or willingness.

With the negative form, this ambiguity mostly disappears because:
    I can't help you with your homework
implies inability rather than unwillingness as does:
    I couldn't help her
In order to state unwillingness, we have to use the modal auxiliary will:
    I won't help you with your homework
    She wouldn't help her with her homework


will / would: the multi-faced verb

Much confusion can be avoided if the verb will is considered polysemous (i.e., having two or more meanings).  In English the verb can, among other things, express

  1. Futurity (a non-modal use) as in, e.g.:
    1. I'll be 50 tomorrow
    2. The train will arrive at platform 6
    3. When will the train arrive?
    4. I won't see him tomorrow
  2. Certainty or likelihood (epistemic modality) as in, e.g.:
    1. That'll be the postman
    2. This'll be a long job
    3. This won't take long
    4. Will it rain?
  3. Willingness (a dynamic modal use) as in, e.g.:
    1. I'll help you
    2. She'll read you a story
    3. Will you marry me?
    4. She won't tell me the truth

We are only concerned with the last of these here.  These meanings are quite different and mixing up examples of the three functions in the same classroom presentation can bewilder learners unnecessarily.

The situation is similar with the verb in the past, would.  It can, among other functions, signify:

  1. Distancing and politeness
    1. Choosing
          Would you help?
          Will you help?
      or choosing
          If I give you the money will you buy it for me?
          If I give you the money would you buy it for me?
      implies greater politeness and tentativeness although both refer to current willingness
  2. Indirect speech
    1.     I'll do that for you
      is reported (at another place and time) as
          She said she would do it for me
      but both refer to her willingness
  3. The habitual aspect
    1. He would often complain
      expresses a habitual or repeated action and is not to do with (un)willingness at all.


Because the verb will / would is polysemous (i.e., having more than one connected meaning), there is scope for ambiguity to arise.
For example, in:
    Will you marry me?
there is no ambiguity because the speaker is clearly referring not to ability but to willingness but in:
    Will he marry her?
the speaker may be referring to the future likelihood of him marrying her or to his willingness one way or the other.  Without a context, we cannot know.
And in:
    He would be rude to her
the speaker may be referring to habitual actions, futurity in the past or to the likelihood that he may choose to be rude in the future.  We cannot know without context.


Expressing ability

The verb can is often the first modal auxiliary verb, along with must, that learners encounter in English.  It expresses a simple and fundamental concept and is, in the present tense at least, uncomplicated so we have, simply:

In the present tense, all these instances of can are replaceable with a copular verb (usually be) and the adjective able plus to:

although the use of the able-to formulation is less common and more formal.  When no difference in meaning exists, English speakers will usually prefer the modal auxiliary.
Other copular verbs make subtle changes to the meaning but the sense remains:

That this formulation is analysable, and teachable, as copular verb phrase + adjective phrase + to-infinitive verb phrase (plus the object if any) is revealed by the parallel forms such as:

and so on.

So common is the concept that the verb can is often directly translatable into a range of languages and so fundamental is it that many languages simply attach a prefix or suffix to the verb to express the concept.
English is, however, unusual in that can is defective, and has no future form at all and only a restricted past form, could.  The use of the adjective in be able to is the workaround in English so we get, e.g.:
    Were you able to see the doctor?
    I won't be able to come tomorrow



Expressing ability in the past

In the past tense, however, things become a little more difficult.


General and specific abilities

  1. A general ability in the past can be expressed either with could or was / were able to:
        I could speak French when I was 10 = I was able to speak French when I was 10
        When I worked in London, I could catch the train to work = When I worked in London, I was able to catch the train to work
  2. However, if we refer to a specific instance of success, only was / were able to is possible:
        He was able to say the word in French
        *He could say the word in French
    Other specific instances of an ability can be expressed with other formulations, often verb processes such as:
        We succeeded in getting tickets
        They managed to catch the train
    But not, usually:
        *We could get tickets
        *They could catch the train

Three exceptions

  1. Verbs of perception can be expressed as abilities in the past with no sense of whether it is a general or specific ability to which we refer.  E.g.:
        She was able to hear the telephone ringing = She could hear the phone ringing
        He was able to see the harbour = He could see the harbour
        I couldn't understand him = I wasn't able to understand him
  2. With negative-sense adverbials.  E.g.:
        I was hardly able to hide my feeling = I could hardly hide my feelings
        They were only able to find expensive tickets = They could only find expensive tickets
  3. With subordinate clauses.  E.g.:
        They were delighted she could come = They were delighted she was able to come
        He said he couldn't come before 6 = He said he wasn't able to come before 6

Fulfilled and unfulfilled ability

In the past, the perfect form of could implies an unfulfilled ability but the was / were able to formulation implies a fulfilled ability.  For example:

In the negative, could have usually refers to possibility, rarely to ability, so it is not easily usable for dynamic modality.  The statement:



Because can and could are used for a variety of functions apart from dynamic modality concerning ability, there is often no easy way to disambiguate.  For example:

Example Possible modality
You can talk to him Deontic: giving permission to talk to him
Dynamic: expressing ability assumed in another
She could explain clearly Dynamic: expressing her ability in the past
Deontic: expressing the fact that she should explain
Epistemic: expressing a future likelihood
You can't be serious Dynamic: expressing frustration at another's inability
Epistemic: expressing the speaker's view of the truth of a proposition
It could bend Dynamic: stating a fact about the material
Epistemic: stating a possible outcome
Can you be quiet? Dynamic: Are you able to be quiet?
Deontic: Please be quiet!
She could have driven faster Dynamic: she had the ability to drive faster
Deontic: she should have driven faster
You could have told me Dynamic: you had the ability to tell me
Deontic: you should have told me
Epistemic: you may have told me but I don't remember

Only the context and understanding of speaker intentions along with some knowledge of the shared information can determine which meaning is appropriate.


Other ways to express dynamic modality

Because of the ambiguities which are rife with the two modal auxiliary verbs we have discussed, especially in positive clauses, whenever there is a need to disambiguate what is meant, native speakers will often resort to non-modal-verb ways to express the concepts of dynamic modality and (un)willingness or (in)ability.
There is a guide, linked below to non-modal-verb modality which contains more detail.  Here some examples will suffice:

  1. Expressing willingness:
    1. Verbs
          I want to help
          She is offering to help
          They are proposing to give us a hand
          I refuse to help
          I don't want to come
    2. Adjectives
          I am willing to help
          She is keen to come
          I was eager to go
          They are reluctant to interfere
          I am loath to ask
          He is half-hearted about doing it
          I am delighted to help
          She is happy to lend us the money

          They are averse to eating out
    3. Adverbs
          They came willingly
          He accepted eagerly
          She arrived reluctantly

    4. Nouns
          He showed little commitment
          Her eagerness to meet him was obvious
          His reluctance to come was clear

  2. Expressing ability:
    1. Verbs
          He was able to come
          They achieved the success they wanted
          She failed to win the prize
          I managed to do it
          It worked!
          He succeeded
          They persuaded me
          It demonstrated its value
          They attained the goal

    2. Adjectives
          It was ineffective
          That was a fruitful meeting
          It was a productive idea

    3. Adverbs
          He managed it successfully
          They worked effectively
          She operated productively

    4. Nouns
          His success was welcome
          The outcome was positive
          That was a fine accomplishment


Many non-modal-auxiliary-verb ways of expressing dynamic modality are more formal versions and often used in writing in which context is limited and the scope for ambiguity is wider.

Related guides:
non-modal-verb modality covers some of the above and extends it to include epistemic and other forms of modality
epistemic modality which follows a similar format to this one
deontic modality which follows a similar format to this one
multiple modalities for a guide which considers how different types of modality may be combined in single utterances
ambiguity for a guide which considers the polysemous nature of many modal auxiliary verbs and the ambiguity which can arise
the modality map for more choices

Palmer, F. R, 2001, Mood and Modality, 2nd edition, Cambridge: Cambridge University Press
Proctor, P (Ed.), 1995, Cambridge International Dictionary of English, Cambridge: Press Syndicate of the University of Cambridge