Ability vs Capability

Dear ameyagmat1989,
I'm happy to respond.

You definitely do not need to worry about this distinction for the GMAT. The GMAT SC occasionally uses "able" and "ability", but the words "capable" and "capability" are much more rare. The word "able" means someone can do something, and it usually strongly implied that they have already done it. If I say, "My friend can speak Arabic", that certainly implies that in the past, he actually has spoken Arabic at the very least on one occasion. By contrast, the word "capable" is most often used in hypothetical senses --- "the suspect is capable of murder" --- this tends to imply: we don't know whether he has already done it, but he could do it in the future. These are general rules, but again, I have NEVER seen an official question testing this distinction.

Here are some GMAT Idiom flashcards:
https://gmat.magoosh.com/flashcards/idioms
Those contain distinctions the GMAT does expect you to know.

Does all this make sense?
Mike