Hi!
I've found some examples that show the difference between could and was able to.
- We use
could have to say we were able to do sth, but in fact we didn't.
He could have helped me, if he'd tried. (= but he didn't)
- For general ability in the past we also use
was able to, though
could is more common.
I could/was able to swim when I was five years old.
- For a specific event showing success after trying, we use
was able to, managed to, or succeeded in, but
not could.
I was able to/managed to solve her problems for her.
- We use
couldn't have to say we were not able to do sth so we didn't.
He couldn't have helped me anyway. (= he didn't)
I hope this will help you. Good luck!
