Updated: Aug 3, 2022
These verbs are used to express various functions which you can read about in this article below.
BE ABLE TO
- is used in cases where can/could is not grammatically possible because it has no infinitive or participles for example to express perfect tenses or future:
I will be able to pick you up at 10 o'clock. (Not… I will can…)
Charles hasn't been able to come by because he is stuck at work.
- after modals such as might or should
Lenka might be able to help you.
You should be able to see the castle from the balcony.
- after verbs want, hope, or expect
She hopes to be able to win the race.
Do you really expect to be able not to make any mistakes?
- to talk about general ability in the present or past
I am able to speak three languages.
I was able to play the guitar when I was younger.
--> can is used more often unless it cannot be used like in these tenses:
I haven't been able to sleep recently.
I might be able to run the marathon.
- to say that someone did something in a specific situation: be able to / managed to
There was an earthquake but we all were able to/managed to hide.
- be able to is not often followed by passive infinitives, can is:
Marketa can't be trusted. John can't be understood.
- is more formal than can
CAN= 'know how to'
Cannot - is a written negative form, written as one word, used as the emphatic form
Can't - is a spoken negative form
1) With verbs referring to perception: see, hear, feel, smell, taste + remember, understand
To talk about seeing, hearing etc. at a particular moment, we use can see, can hear etc. not -ing form:
I can hear loud music coming again from my neighbours.
I can see the delivery van coming.
I can see you.
He can smell something burning.
I can taste something funny in the soup. What did you put in?
2) With verbs guess and tell:
Can you tell if he's Czech or Slovak?
I could guess what he wanted.
3) To make general statements about what is possible
Winters in the Czech Republic can be quite cold.
You can get to Brno easily by train or bus.
4) To say something is impossible - can't | cannot
This can't be true.
You can't be serious.
Anything can happen.
5) Skills or general abilities
I can speak three languages.
Mary can't sing.
6) PERMISSION / REQUESTS / OFFERS
Could is more polite but works the same way
Can I go to the party with my schoolmates? (permission)
Can I ask a question?(permission)
Can you carry my suitcase, please? (request - less polite)
Can I help you? (offer)
You can go.
You can borrow my car.
You can't leave yet. (refusing permission)
It is used in conditional sentences
Could cannot be used to talk about single events that happened in the past
negative form: couldn't
1) PAST ABILITY
'Be able to' can be used too
somebody had the ability or was allowed to do something
I could speak German well when I was in high school.
My grandma could perform many dangerous stunts when she was younger.
*a specific situation in which somebody succeded in doing something --> managed to
or was/were able to
1 - Monika was a great boxer when she was in her twenties. She could win most of the
matches. (She was good enough to win many matches as she had the ability.)
2 - Monika had a match last week with her fierce opponent, but she managed to win
over her. (Monika succeeded in winning over her oponnent this time.)
Present/Future: could (something is possible, but not certain)
It could be him who stole the car.
The financial situation could get worse.
Past: could have + -ed
Jonathan couldn't have been in the store because he was out of the country.
Margaret could have ended up in jail for starting the forest fire.
We can also use may/might
You could come with us on holiday.
Derek could go to Italy instead of Greece.
What shall we do this weekend? - We could go to the theatre.
4) POLITE REQUEST / PERMISSION
- Usually referring to the near future
- We can also use can/may/might
- To give or refuse permission we use can not could
Could I borrow your car this weekend? Yes, you can./ No, you can't.
Could I get another piece of the cake?
Couldn't you help me carry this?
Couldn't she sleep over?
5) CONDITIONAL FORM OF CAN
If I had more money, I could travel more often. (the 2nd conditional clause)
Dasy couldn't visit us even if she had more time.
If my family had been more supportive, I could have had better school results. (the 3rd conditional clause)
**unrealistic actions - I love this place so much, I could live here for ever.
I am so exhausted, I could sleep the whole day.
FOR ADVANCED STUDENTS:
Couldn't x mightn't
I'm sorry I couldn't drive you to the hospital. (It was not possible to do it.)
I mightn't take you to the hospital. (I do not know yet if I can take you.)
*Past achievement / A specific situation → managed to or was/were able to in positive clauses are used (These are facts, rather than possibilities.)
I was able to / managed to build the whole shed at the weekend.
Guessing and predicting
Must → couldn't as its negative form
Must have + -ed → couldn't have + -ed
Jane must have called her ex. It couldn't be true.
Couldn't / couldn't have + -ed express strong possibility
A single wild boar couldn't have done so much damage in the crops.
Lastly, here are some phrases with could you can use:
…couldn’t be better/worse/nicer etc. → Your choice couldn't be worse.
… couldn’t ask/wish for… → I couldn't ask for a better boss.
… couldn’t care less → I couldn't care less.
I couldn't agree more.
More about the modal verbs:
https://learnenglish.britishcouncil.org/grammar/english-grammar-reference/can-and-could (exercises are at the end of the page)