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Possibility
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Can + present infinitive: General/theoretical possibility. Not usually used for a specific situation.
For dessert you can have apple-pie or ice-cream.
Could/May/Might + present infinitive: Possibility in a specific situation.
He should keep that souvenir - it may be valuable one day.
Note: we can use can/could/might in questions
BUT NOT may. Do you think that he can/could/might fix it?
Could/Might/Would + perfect infinitive: Refers to sth in the past that was possible but didn't happen. He might have succeeded if he had tried harder.
Ability/Inability
We use the following verbs to talk about ability:
| Present | can, can't, be able to, manage to | I can't swim. |
| Past | could, couldn't, he able to, manage to | They weren't able to find out his name. |
| Perfect | be able to, manage to | Ha ve youmanaged to finish the report yet? |
| Future | be able to, manage to | I won't be able to meet you later. |
Can expresses ability in the present/future. I can lean play the piano.
Could expresses general, repeated ability in the past. I could talk when I was two.
Was(n't) able to expresses (in)ability on a specific occasion in the past. I was(n't) able to get to the airport in time to catch my flight.
Couldn't maybe used to express any kind of inability in the past, repeated or specific. I couldn't speak French when I was two. I couldn't/wasn't able to remember his name when I saw him in the street.
Logical Assumptions/Deductions
Must, may, can't, etc + bare infinitive: for assumptions about the present.
perfect infinitive: for assumptions about the past.
Must = almost certain that this is/was true. (= very likely)
She's been working all day, so she must be really tired!
She was working all day yesterday, so she must have been really tired!
May/Might/Could = possible that this is/was true. (= possible)
John isn't at work today - he may/might be out of town on business.
John wasn't at work yesterday - he may/might have been out of town on business.
Can't/couldn't = almost certain that this is/was impossible.(=very unlikely)
That can't be Janet over there - she's at her grandparents’ at the moment.
That can't have been Janet you saw - she was at her grandparents' at that time.
Could, may and might express the same degree of possibility:
He may/might/could remember some things already.
Couldn't expresses the same probability as can't. It is usually used to talk about the past:
The police realised he couldn't be Canadian. (= it was very unlikely that he was Canadian)
!!! May not and might not do not express the same probability as couldn't:
The supermarket may/might not be open today because it's a Bank Holiday, (not the supermarket couldn't be open)
Present. We use:
· may (not), might (not), could(n't), must, can't + bare infinitive to talk about possibility in the present:
He may remember some things already. (= it is possible he remembers some things now)
It can't he very easy living with someone who doesn't remember any of the past. (= it is very unlikely that it is easy)
· may (not), might (not), could(n't), must, can't + be + -ing to talk about things (possibly) happening or in progress at the time of speaking:
They must be having a difficult time adjusting to it all.
The phone is engaged. She might be talking to her sister on the phone.
Past
· may (not), might (not), could(n't), must, can't + have + past participle to talk about possibility in the past:
In the attack he must have hit his head. (= there is strong evidence that he hit his head)
He could have had a wife and children, (this is a possible situation)
He can't have been married. (= there is strong evidence that he wasn't married)
· may (not), might (not), couldn't), must, can't + have been + -ing to talk about things possibly happening or in progress in the past:
He might have been trying to run away from his past.
Future
· may (not), might (not), and could (not) + bare infinitive to talk about possibility or uncertainty in the future:
He could make a total recovery one day.
· may (not), might (not), could (not), must, can’t + be + -ing to talk about things possibly happening at a time in the future:
I might be meeting John later.
Alternatives to modals
Adverbs like certainly, probably, possibly, perhaps and maybe can be used to express similar ideas to modal verbs:
He had probably been attacked and robbed. (= he must have been attacked)
We can use it + be + certain/likely/probable/possible/impossible to express ability, probability and possibility:
It is possible to program your computer to translate texts automatically. (= you can program your computer)
It is possible that the train will be late. (= the train might be late)
Note how the tenses of the infinitive are formed:
Present simple: (to) cook
Present continuous: (to) be cooking
Present perfect simple: (to) have cooked
Present perfect continuous: (to) have been cooking
Дата публикования: 2015-01-09; Прочитано: 1861 | Нарушение авторского права страницы | Мы поможем в написании вашей работы!
