There is a small difference between ‘was able to’ and ‘could’. Take a look at the following sentences:

· He was able to go to London yesterday and he enjoyed himself very much.

· He didn't agree with me at first, but I was able to persuade him.

· He was able to leave Europe before the war began.

Do you think we can substitute the phrase ‘was able to’ in the sentences above with the word ‘could’? If not, why not?

Please join Li and Catherine for a full explanation of the subtle differences between ‘was able to’ and ‘could’.