to be able to do something or to know how to do something:
You can swim, can't you?
Even a small personal computer can store vast amounts of information.
Gabriella can speak French fluently.
I'm afraid Mr Harding can't see you now - he's busy.
The police are doing all they can to find her.
spokenused to ask someone to do something or give you something:
Can I have a cigarette, please?
Can you help me lift this box?
to be allowed to do something or to have the right or power to do something:
You can't park here - it's a no parking zone.
'Can we go home now, please?' 'No you can't.'
Any police officer can insist on seeing a driver's license.
used to say that something is possible:
I am confident a solution can be found.
There can be no doubt that he is guilty.
The boxes can be stored flat.
Can he still be alive after all this time?
used with the verbs 'see', 'hear', 'feel', 'taste', and 'smell', and with verbs connected with thinking, to mean that someone sees something, hears something etc:
Here they are - I can see their car.
Can you smell something burning?
I can't understand why you're so upset.
He can't remember where he put the tickets.
[in negatives]used to say that you do not believe that something is true:
This can't be the right road.
It can't be easy caring for a man and a child who are not your own.
[in questions and negatives]used to say that someone should not or must not do something:
You can't expect the world to change overnight.
We can't go on like this.
Jill's left her husband, but can you blame her after the way he treated her?
[usually in questions and negatives]spokenused when you are surprised or angry:
You can't be serious!
They can't have arrived already, surely!
How can you be so stupid!
used to say what sometimes happens or how someone sometimes behaves:
It can be quite cold here at night.
Peter can be really annoying.
spokenused to tell someone in an angry way to do something:
And you can stop that quarrelling, the pair of you.
If you won't keep quiet, you can get out.
WORD CHOICE: WORD CHOICE: can, could, be able toUse can and be able to to say that someone has the ability to do something. Be able tois more formal• Can you swim? • Young children are not able to open the bottle.Use couldto say that someone has the ability to do something, but does not do it• He could do a lot better.Could is also the past form of can. Use could or a past form of be able toto say that someone had the ability to do something in the past• She could ride a bike when she was three. • He was able to walk with a stick.!! In the following cases, you cannot use can. You must use be able to:with used to, to say that someone had the ability to do something in the past but no longer does• I used to be able to play the violin. to talk about future ability. Use will be able to• After only a few lessons, you will be able to understand basic Spanish. after other verbs, for example might, may, would, want, or hope• He might be able to fix your car. • You should be able to taste the difference.• I want her to be able to use a computer.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.