What gets me as a non-native speaker far more than "a vs an" is the "a vs the" conundrum. I still don't quite get when something needs to be "indefinite" and I've been speaking English for close to forty years. My native tongue lacks articles altogether and it's soo bloody hard I feel hopeless I'll ever master them fully.
That rule isn’t universal though. “I go to the dentist every year” doesn’t imply that I particularly care about a specific dentist (or, case in point, about the specific dentist).
“This was a nice evening” is also difficult to characterize as not caring about which evening it is. As are books titled “An Introduction to XYZ”, where both the authors and the readers will probably care about the specific book.
Beyond that, there are cases where you absolutely are referring to a specific one, but use a/an.
"Our house has a pool" for example. There is a very specific pool being referred to, but it's sufficiently indirect that "the" would never be used here without radically changing sentence meaning.
abraxas · · focus · HN ↗
AndrewDucker · · focus · HN ↗
"Pass me a plate" - any plate will do. "Pass me the plate" - I want the specific plate which we were talking about.
layer8 · · focus · HN ↗
“This was a nice evening” is also difficult to characterize as not caring about which evening it is. As are books titled “An Introduction to XYZ”, where both the authors and the readers will probably care about the specific book.
margalabargala · · focus · HN ↗
"Our house has a pool" for example. There is a very specific pool being referred to, but it's sufficiently indirect that "the" would never be used here without radically changing sentence meaning.
necovek · · focus · HN ↗
It's like saying "our house has a roof" — very similar, but nobody really cares about the roof, the focus remains on the house.