He can play tennis well.
She is able to speak five languages.

They can come on Friday.
Jack will be able to come next week.

از can و be able to برای صحبت از توانایی و احتمال استفاده کنید.

نکته: آینده be able to فعل will be able to  است.

He could swim when he was five.

could  در مفهوم گذشته به معنی توانایی است.

They were able to get tickets for the concert.

I was able to finish before 6.

I couldn't come last night, sorry. OR I wasn't able to come last night, sorry.

مهم: اگر شخصی در جایگاه انجام چیزی باشد یا بتواند از عهده چیزی برآید به جای could از was/were able to استفاده می کنیم.

در حالت منفی wasn't able to و couldn't هر دو درست هستند.