Can / Could / Be Able to

Listed below are some examples and uses of "can", "could", and "be able to" in regard to ability.

Examples	Usage
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.	Use 'can' or 'be able to' to express an ability or possibility NOTE: The future of 'be able to' is 'will be able to
He could swim when he was five.	"Could" in the past indicates the general ability to do something.
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.	IMPORTANT: If someone had the capacity to do something or managed to do something on a specific occasion in the past, we use "was/were able to" instead of "could". -- However, in the negative, "wasn't able to" OR "couldn't" are both correct.

Self-check QUIZ: Can / Could / Be Able To

Think of whether you should use "can", "could", or "be able to" to complete the following sentences. Click on the arrowhead to check your answer.

Tom (buy) a new house last month.

(they/play) tennis well?

She (not/understand) the question yesterday.

Fred (speak) Russian when he was six years old.

When (you/come) tomorrow?

Unfortunately, they (get) the bread this morning.

I (not / play) golf last Thursday.

(you / speak) Japanese?

(he / come) to the party next weekend.

They (get) tickets to the Rolling Stones concert last week.

How (you / convince) him to come to the exhibition last week?

She (enjoy) the concert because of the noise outside.

Adapted from http://esl.about.com/library/grammar/blcanbeable.htm