Can vs. could vs. to be able to (ability, possibility) (Modal verbs p.1)
Дата публикации: Dec 14, 2015 4:5:23 PM
1. Oxford Learners Dictionary Grammar Point
can / could / be able to / manage
Can is used to say that somebody knows how to do something: Can you play the piano?
It is also used with verbs of seeing, noticing, etc: I can hear someone calling, and with passive infinitives:The podcast can be downloaded here.
Can or be able to are used to say that something is possible or that somebody has the opportunity to do something: Can you/are you able to come on Saturday?
You use be able to to form the future and perfect tenses and the infinitive:
You’ll be able to get a taxi outside the station.
I haven’t been able to get much work done today.
She’d love to be able to play the piano.
Could is used to talk about what someone was generally able to do in the past: Our daughter could walk when she was nine months old.
You use was/were able to or manage (but not could) when you are saying that something was possible on a particular occasion in the past:
I was able to/managed to find some useful books in the library.
(not I could find some useful books in the library).
In negative sentences, could not can also be used:
We weren’t able to/didn’t manage to/couldn’t get there in time.
Could is also used with this meaning with verbs of seeing, noticing, understanding, etc:
I could see there was something wrong.
Could have is used when you are saying that it was possible for somebody to do something in the past but they did not try:
I could have won the game but decided to let her win.
2. Adv. Grammar in use
3. R.Quirk
ABILITY
CAN, COULD and BE ABLE TO
a) Present.
Can is m ore com monly used than be able to to express ability.
Example: I can drive but I can’t ride a bike.
How m a ny mi stakes can you find in m y reproduction?
b) Past.
In affirm ative sentences there is an im portant difference in meaning between could and was/were
able to . Could r e f e r s t o g e n e r a l ability whereas was/were able to i s u s e d i n c a s e s o f s p e c i f i c ability.
Example: W henever you passed their house you could hear them arguing.
I could never fi nd a taxi when I wanted one. (general ability)
We re you able to find a taxi after our high school party? I was able to concentrate on my essay
because nobody disturbed me last night, I was alone at home . ( s p e c i f i c ability)
In negative sentences could is norm a lly used in both general and specif i c cases of ability.
Example: The sea was so polluted that we couldn’t swim .
I couldn’t walk until I was two and a half .
c) Perfect and Future are formed with be able to because can has no infi nitive or past participle.
Example: I’ll be able to visit you m ore often next week.
She hasn’t been able to solve the puzzle yet.
Sim ilarly, be able to is the only possible inf i nitive.
Example: I’d like to be able to offer you job but there are no vacancies at the m ome nt.
d) Could have done. Could + the Perfect Infinitive is used to show that some one had ability to do
som e thing but didn’t do it.
Example: She could have been a good doctor but she becam e an accountant instead.
He was so rude with his children I could have told him off.
+
Did you hear? vs. Have you heard?
CAN (CAN'T = CANNOT) - физическая возможность, данность, умение, а также наличие/отсутствие условий для реализации действий.
I can read. - Я умею читать.
I can't read. - Я не умею читать. (потому что не научен) или Я не могу читать. (потому что темно)
MUST (MUSTN'T = MUST NOT) - обязанность, долг, срочность выполнения действия, запрет
I must read these books. - Я должен прочитать эти книги. (потому что иначе не сдам экзамен)
I mustn't read aloud. - Я не должен читать вслух. (потому что дедушка спит)
SHOULD (SHOULDN'T = SHOULD NOT) - совет, рекомендация, упрек
You should read more. - Вам бы/неплохо бы/не помешало бы побольше читать. (если хотите получить пятерку вместо четверки)
You shouldn't read this book. - Эту книгу читать не следует. (потому что она неинтересная)
WILL (WON'T = WILL NOT) - обязательное действие в будущем, обещание, прогноз, отказ от действия, обязанности и т.п.
I will read this book. - Да прочитаю я эту книгу.
I won't read this book. - Да не буду я читать эту книгу.