can/could/be able to (ability and possibility)
Can is a modal verb. It only has a present, past, and conditional form (but can also be used with a future meaning).
I can speak Spanish very well.
She could play the violin when she was three.
She can't come tonight. She's ill.
They couldn't wait because they were in a hurry.
Could you open that door, please?
You can use be able to in the present, past, future, present perfect, and as a gerund or infinitive.
be able to in the present and past is more formal than can and could.
I am able to accept your invitation.
They weren't able to come.
I'll be able to practise my English in London.
She has been able to speak French since she was a child.
I'd like to be able to ski.
I love being able to sleep late at weekends.
Modals - Can
Modals - Could
Modals - Be able to
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