Man, you Irishters can’t spell for shite. Ya’all need to brush up on your pronunciation rules. 
Here’s what I said in my 1st post here “Either is OK, since both are understandable and both are in common usage. Other than those two “rules” there are no “official” rules for American English Grammar.”
Just to add:
Both “a” and “an” are derived from the number “one” (or more correctly, its Old English etymon, ân). Their pronunciation evolved separately because “one” is usually stressed while a(n) is usually unstressed. This isn’t terribly relevant to the debate at hand, but I bring it up because “a” is a further reduction / shortening of “an” before consonants and semivowels; historically, the [n] was taken away rather than added. Right now, “a” is used before everything except pure vowels, but at some point in the past “an” must have been used before everything. The only questions are: When did “a” start to be used on its own? Was there a point when “a” was used before consonants but “an” before words beginning with the h-, w-, and y- sounds? If so, when was that?
First of all, it is NOT true that “both” are in “common” usage. I think what you mean to say is that both are used to some extent as if they are “correct.” But even that’s a bit difficult to pin down; after all, most people who use poor grammar don’t think of themselves as breaking rules when they speak, and just because their locality uses a particular idiom that is otherwise violative of the rules isn’t perhaps enough to make it “correct,” except, of course, among their own locality.
Your main point is that no one says “Thou Shalt Not Use …” in English, in some formalistic sense. But that’s true of most languages. Still, as Chronos notes, one can use something in a way that can be understood, but is still “incorrect” in that the people who use the language daily think of it as not a correct manner of speaking or writing. Whether or not “an euphamism” falls into that category is still, perhaps, up for debate.
Geez Louise, it was a simple enough question. Just let the damn thread die, wouldja?
It’s lucky you bumped the thread again to make your point.
The most common example I can think of here is “an historian” which is a relatively common usage. Saying it aloud, I find that I tend to omit the [h] (as in hat) entirely, beginning the word ‘historian’ with the * (as in fi t) with the emphasis on the second syllable.
I’m not going to bother with the phonetic alphabet, but essentially ‘historian’ becomes: iss-TOR-ee-en. When I do that, the initial voiced phoneme is the * - the same vowel sound as the beginning of ‘idiom’ - thus, “an”.
Anyway, I also tend to soften the [h] sound in “humanitarian” - the initial voiced phoneme doesn’t end up sounding like “oo” or “uh” but more like “ew” - still a vowel sound, though, so I can see “an humanitarian” (when I say it aloud I run it together so it sounds like “a new manitarian”.
And we don’t say “an year” because the initial voiced phoneme is [j] - a consonent sound.
(Sorry to bump again - just wanted to address that humanitarian thing.)