CAN, COULD, OR BE ABLE TO?

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)

COULD

• It is used in conditional sentences

• Could cannot be used to talk about single events that happened in the past

• negative form: couldn't