Structure of Can, Could and Be able and their usage in different contexts.

1. Can, Could & be able to

2. Introduction
Modal auxiliaries or modals (can, could, may, might,
must, ought to, shall, should, will, and would) are used
to express the meanings of necessity, advice, ability,
expectation, permission and possibility, etc.
The combination of helping verbs with main verbs
creates what are called verb phrases or verb strings.
They are used in conjunction with main verbs to
express shades of time and mood.
The shades of meaning among modal auxiliaries are
multifarious and complex.

3. Modal auxiliaries do not change form for different
subjects.
For instance, try substituting any of these modal
auxiliaries for can with any of the subjects listed below.
I/you/he/we/you/they can write well.

4. Present

5. Structure
S + Can + V(1) + O
I can speak English

6. Where to use can
We use can to say that some thing is possible,
someone has ability or an opportunity, or some one
knows that some thing is possible for him/her to do it.
Can is used to express ability (in the sense of being able
to do something or knowing how to do something):
He can speak Spanish but he can't write it very well.

7. Where to use can
Can is used to express permission (in the sense of
being allowed or permitted to do something):
Can I talk to my friends in the library waiting room?
Note that can is less formal than may.
Also, some writers will object to the use of can in this
context.

8. Where to use can
Can is used to express theoretical possibility.
American automobile makers can make better cars if they
think there's a profit in it.

9. Where to use can
We use can for possible future actions.
If we earn some money, we can go on holiday next
summer.
I’m quite busy today. I can’t come to your party tonight.

10. Can or be able to
In the present tense, be able to is little more formal
and less usual than can
How many instruments can youare you able to play?
I can/am able to play piano and violin.
I can/am able to sing various songs
I can walk around now.
Doctor says I can go back to work soon
Ali is good programmer. He can/is able to write computer
programs

11. Can or be able to
In some structures we always use be able to, not can
In present perfect, after a model verb and after to
infinitive.
In present perfect: It has been quiet today. I haven’t been
able to do work.
After a modal verb: Ali might be able to help us.
After to-infinitive: It's nice to be able to go to the opera,
(NOT to-can-go)

12. Other Examples with be able to
I haven’t been able to sleep recently.
I haven’t been able to do anything interesting.
I haven’t been able to come and see you before.
She might not be able to come tomorrow.
I am very busy today, but I should be able to meet you
tomorrow.

13. Past

14. Structure
S + Could + V(1) + O
I could speak English when I was 8.

15. Where to use could
For ability or opportunity in the past, we use could or
was/were able to.
Natasha could play (OR was able to play) the piano when she
was four. (ability)
In those days we had a car, so we could travel (OR were able
to travel) very easily. (opportunity)
The children could swim when they were quite young. (ability)
The children were able to swim across the river.(past action)
My father could speak five languages. (ability)

16. Could have
We can also use could have for an opportunity that
we didn’t take or a possible result that didn’t happen.
Someone could have stole them.
We could have gone out somewhere but we were too
tired.
We were very lucky, there could have been a terrible
accident.

17. Where to use could
We normally use could (not was/were able to) with
the verbs such verbs see, hear, smell, taste, feel,
remember and understand etc.
We could see the village in the distance.
As soon as Ali opened the door he could smell some thing
burning.
I couldn’t understand what was happening.

18. Future

19. Structure
S + Will + Be able to + V(1) + O
I am learning English language, I will be able to
speak English next year.

20. Where to use be able to
For the future we use can or will be able to but not
will can
If we earn some money, we we'll be able to go on holiday
next summer.
I’m afraid I wont be able to come to the disco on holiday
next week.
I’m quite busy today. I won’t be able to come tomorrow.

21. Can or be able to
To suggest a possible future action, we normally
use can.
Let's have lunch together. We can go to that new
restaurant.

22. Other Uses Of can/could

23. Asking permission
We use can, could or may to ask for permission.
Can I use your pen?
Could we borrow your ladder, please? ~ Well, I'm using it
at the moment.
May I see the letter? ~ Certainly.
Could often sounds more polite than can. May is
rather formal.

24. Giving permission
To give permission we use can or may (but not could).
You can wait in my office if you like.
Could I borrow your calculator? ~ Of course you can.
You may telephone from here, (a written notice)
May is formal and is not often used in speech.

25. Refusing permission
To refuse permission we use can't or may not (but
not couldn't).
Could we picnic here? ~ I'm sorry. I'm afraid you can't.
Members may not bring more than two guests into the
club. (written principle of club)
We can also use must not.
Luggage must not be left unattended. (written statement)
Bicycle must not be left unattended. (written statement)

26. Talking about permission
We sometimes talk about rules made by someone else. To do
this we use can, could and be allowed to.
We use can to talk about the present, and we use could for the
past.
Present: Each passenger can take one bag onto the plane.
Past: In the 1920s you could drive without taking a test.
We can also use be allowed to:
Present: Passengers are allowed to take one bag onto the plane.
Past: We weren't allowed to look round the factory yesterday.
Future: Will I be allowed to record the interview on tape?

27. Use of can in asking people to do something
When we ask people to do some thing:
Structure: Can/could you...?.can/could I..?
 Can/could you open the door, please?
Could/can you wait a moment, please?
When we ask people for some thing:
Can/could I have...?
Can/could I have these postcards, please?
Can I have one cup of ice-cream please?

28. Let’s Practice