I just found your reply to me above — since you’d replied to your own comment, I didn’t receive notice of it.
Irish has several ways of expressing “can X”/“able to X”, so the one-to-one correspondence that you’d posited doesn’t actually exist.
Note that there are many possible translations of mar, and “for” would be an incorrect translation of a number of its meanings.
Oh I'm not saying it's wrong; just that if feidir and ábalta are different words, and the latter is derived from the same root as English "able" (Old French "abile"), it might make sense to consistently translate them differently with the nearest equivalent. Context: I'm in favour of always translating mar as "for", even though Duolingo doesn't always like it! After all, "for" can mean "because" in English too.