Can, could, and be able to are used to express ability.

• Can expresses ability in the present

I can speak English but I can´t speak French

• Could expresses ability in the past

I could speak English when I was young.

NOTE: To express ability on one particular occasion in the past we use was/were able to.

The exam was very long but Mark was able to finish it.

• Be able to is used with the rest of the forms

Being able to speak English is wonderful

Is she studies everyday, she will be able to speak English fluently

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