Can - Could and Be able to

We use can, could and be able to:

To talk about natural or learned ability.
It is something that Can,could and Be able to have in common.

We use can to talk about:

ability and possibility
make request
ask for or give permission

We use could to talk about:

Past ability
possibility
polite request
suggestion
conditional of can

We use be able to:

To talk about ability.