I was in a discussion with someone, where they described my wrong use of an article as a "mispronunciation". I argued it was rather a matter of grammar, as I did pronounce the article correctly, but it was the wrong one. I should say now that this isn't the English language we're talking about, we were talking Norwegian at the time.
First of all, I did not use the wrong tense, i.e. using indefinite articles instead of definite, which would definitely be a matter of grammar. My offense is more in the lines of using "a" instead of "an", but not entirely. As you probably know, whether one uses "a" or "an" is based on whether the word in question phonetically starts with a vowel or a consonant. If it starts with a vowel, an "n" is put after the base "a" to make it more appeasing to utter and hear. This is a concept that I believe is quite wide-spread (at least in Indo-European languages), with an example of this in Spanish; it being el agua instead of la agua.
And so, with these languages, I could see that one would call it a fault of pronunciation to use "a" instead of "an", as the very distinction exists for the purposes of refining the "sound of English". But in my case, I was speaking Norwegian, of where the distinction between the articles is not based in any such logic. To be honest, I do not believe there is any logic to it, and if it was, it has disappeared in the evolution of the language into weak and blurry silhouettes of patterns. It doesn't inherently, or according to some establishment of logic, sound better to use the correct articles in Norwegian. Rather, it sounds better because we have been "taught" to use those articles, and we've heard them been used that way many times, and so a deviation from that sounds bad.
I'm not claiming that a foreigner will necessarily find "an" to sound better than "a" in front of a word starting on a vowel, but there is a logic behind it based in phonetics. In Norwegian, there are simply rules saying that "a word constructed such and such shall use those articles respectively". These rules are littered with exceptions, but they exist there. But they're not based in any logic, at least not one present today. And so, it is simply arbitrary grammar in my head, and to use the incorrect article would be a matter of exactly that, grammar. But perhaps it isn't that, but instead a matter of pronunciation. Or maybe both. Or neither. Perhaps there isn't an objective answer at all?