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Modal verbs 1  - verbs of ability

Modal verbs – definitions

Depending on which resource you consult, there are anything between eight and sixteen modal verbs in English, or even more.  So why the confusion? In short it is due to  differences of opinion as to what a modal verb actually is; and grammatical description being an art, not a science, there is no definitive "right" answer to this. The reality of the situation is that there is no universally accepted definition of what constitutes a modal verb and there never has been.
    Modal verbs, or modal auxiliaries, are generally defined as being helper verbs which affect the meaning of a main verb, by adding a modality (quality) to the action, most commonly possibility, probability, obligation or recommendation, or futurity.  Common examples of verbs that match this definition are:
    Possibility or probability: can, could, be able to, may, might
    Obligation: must, have to, should, ought to, need to
    Futurity:  will, shall, would, going to
The expression modal verbs is used in two ways, either narrowly as a syntaxical reference (defined by grammatical usage) or else more broadly as a semantic reference (defined by meaning). Syntaxically, only can could may might must should will shall and would are always labeled as modal verbs. Semantically however, the verbs in blue in the list above  be able to, have to etc (and several more)  also match the classic definition of modal verbs. So while linguists may like to consider modal verbs as a syntaxical category, in the context of language teaching or learning it is more useful to study modal verbs as a semantic family.

Modals of ability or possibility : can may could might, etc.

Modal verbs  are used to express two different types of ability: 

  1. Open possibility, generally expressed by forms of the modal verb Can ( & could), 
  2. Authority or potential ability, usuallly expressed by forms of the modal verb May ( & might), . 

These verbs are followed by the infinitive without to.

Open possibility - can and be able to, could 

The verb can only exists in simple present, simple past and present perfect structures. 

Forms of the verb can
All persons Present Past Present perfect
Affirmative can
could can have + participle
Negative can not, cannot, can't could not,  couldn't cannot have

If other tenses are required, the speaker or writer must use forms of be able to .  Functioning semantically as a modal verb, be able to has all necessary tenses, as it is in reality just the verb to be followed by the adjective able.
N.B. : Be able to is not used in progressive or continuous tenses, though the present participle / gerund being able to is sometimes used.
Sample tenses Present Present perfect Imper­fect Future
Affirmative: am able to,
are able to
is able to
has been able to
have been able to
was able to
were able to
will be able to
sample forms
am not able to ,
am unable to
has not been able to
has been unable to
was not able to
was unable to
will not be able to
will be unable to

Can and able to are used to express :
a1) I  can speak three different languages, English, French and Spanish.
a2) He can't open the door, it's stuck.
a3)  I'm able to speak three languages, German, English and Russian.
a4)  He's unable to get into his car, he's lost the key.
a5)  When I lived in York, I could walk to work in five minutes.
a6)  If you lose the key, you won't be able to get  into your apartment.
a7)  I haven't been able to finish the job, it's too difficult.
a8)  In spite long discussions, they were unable to reach an agreement.
a9)  Being able to speak English well is a useful skill !
b1)  The policeman says we can go in now.
b2)  Can we please sit down !
c1)   They cannot have seen the warning sign
d1)   I could see it a minute ago, but I can't see it now.
d2)   You could come and see us tomorrow, couldn't you? 
d3)   I could have finished the whole test if I'd had five more minutes.
Attention !  
Take care to distinguish correctly between  "could not" and "cannot have"
They could not see the warning sign
   = They were unable to see it, for example, because it was hidden
They cannot have seen the warning sign.....  
   = They must have failed to see it, even though it was there and visible.

Potential possibility or authority - may and might 

The verb may only exists in the simple present, and past forms The simple past form of may is might .  
is also used in its own right as a present tense modal.
Forms of the verb may
All persons Present Past Present perfect
Affirmative may
might may have
Negative may not might not may not have
Forms of the verb might
All persons Present Past Present perfect
Affirmative might
might might have
Negative might not might not might not have

a1) We may (perhaps) go to England next year, if we have enough money.
a2) But of course, we may not be able to afford it.
a3) The policeman said "You may go now".
a31) The policeman told me I might go.
a4) "I may not be able to get home on time."
a41) She said she might not be able to get home on time.
b1) I may have left my mobile phone on the train.
b2) It's five o'clock; they may have finished by now.
b3) I may have seen something very important.
c1) I might find a job if I'm lucky.
c2) I think they'll get the contract, but they might not.
c3) I might be able to get tickets for the show tonight, it's just possible !
d1) You're very lucky to be alive; you might have died !
d2) I'm afraid that someone might have heard us.
d3) I might have won if I'd run just a little bit faster.
d4) You might not have broken it if you'd been a bit more careful.
e1) (Please) may I say how happy I am to be here !
e2) Might I ask what you are doing ?

More modals: Modals of obligation - must, should etc.
► Modals of futurity : See Expressing the future
Would used as a past auxiliary: Expressing past habits
► More on negative structures in English
Learning resource: song (text + audio): I would if I could (intermediate English).

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Les verbes modaux en anglais


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