Can, could, and be able to

 

We use can (do) to say that something is possible or that someone has the ability to do something. The negative is can't (cannot).

• You can see the ocean from our bedroom window.
• Can you speak any foreign languages?
• I'm afraid I can't come to your party next friday.

Be able to is possible instead of can, but can is more usual.

• Are you able to speak any foreign languages?

But can has only two forms: can (present) and could (past). So sometimes you have to use be able to.

• I haven't been able to sleep recently. (can has no present perfect)
• Sue might not be able to come tomorrow. (can has no infinitive)
• I'm very busy today, but I should be able to meet with you tomorrow.

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