Modal verbs of ability : can and may
Modal verbs of ability are used to express two different types of ability: open possibility, generally expressed by forms of the modal verb Can, and authority or potential ability, generally expressed by forms of the modal verb May. These two verbs are followed by the infinitive without to.
Open possibility - can and be able toThe verb can only exists in the simple present, simple past and present perfect forms.
If other tenses are required, the speaker or writer must use forms of the synonymous modal verb "be able to" . This modal auxiliary has all necessary tenses, as it is in reality just the verb to be followed by the adjective able.
N.B. : Be able to does not have any progressive or continuous forms.
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.
b1) The policeman says we can go in now.
b2) Can we please sit down !
c1) They cannot have seen the warning sign.....
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 mightThe verb may only exists in the simple present, and past forms The simple past form of may is might . Might is also used in its own right as a present tense modal.
Forms of may
a) The modal may is used to imply potentiality (limited possibility) or authority to do something. Using the modal may is frequently the same as qualifying a statement with the word perhaps. Its past form might is most commonly found in dependent clauses, notably in reported speech.
Note that a synonym of perhaps is maybe.... which is of course composed of the words may and be.b) Used in the present perfect form (may + have + past participle), may is also used to express possibility that occurred (something that perhaps occurred) in a relative past , i.e. in past time with relation to the present or to some other moment.
c) Might is also used to imply remote possibility, i.e. something that could just be possible. In this sense, it is often combined with be able to.
d) Used in the present perfect (might + have + participe passé), might is also used to express a hypothetical possibility (affirmative or negative) in the past. This is particularly common in type 3 conditional clauses.
e) Might and may can both be used to imply politeness or sarcasm.
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 ?
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