"Aren't" instead "am not" for first person singular

Question

I often notice that instead of "am not" the "aren't" version is used and I wonder if that is truly acceptable. What confuses me is that in school we were taught that the short version of am not is amn't and so this is correct and plain clear but when I see "aren't" I just can't stop thinking that it's a contraction for "are not" and is plain wrong for first person singular. I tried to search some grammar but all they say is that it's correct:

However, for first person pronoun, I, there is no contraction with the verb be + not. (“Amn’t” is not a word in English.) Therefore, in casual speech and writing, English speakers use aren’t, instead, and except in formal situations, this is considered entirely grammatical.

And

Because of this authoritative connotation, another way of saying “am I not” developed. Virtually all native speakers now use the form “aren’t I”, which is now completely acceptable in any spoken or informal written context.

I also sometimes stumble upon "ain't" but I know that it's very informal and should be avoided at all costs.

Consider the following:

• I am lucky, am I not?
• I am lucky, amn't I?
• I am lucky, aren't I?
• I am lucky, ain't I?

My question is: Can we use "amn't" in regular speech? Is "aren't" informal or formal and is it an exception in grammar?

Answer 1

There are several possible contractions, none of which are acceptable to all speakers. The only thing that is fully acceptable to everyone is am I not?.

The contraction amn't is used only in Scottish and Irish English. Most North Americans have never heard it, and unless I'm mistaken, most English people readily identify it as Scottish.

The contraction ain't I? used to be acceptable, but because of the condemnation of he ain't for "he hasn't/isn't" and other uses of ain't, the phrase ain't I? became tainted by association. Now you can't say "ain't I?" without sounding uneducated to many people. This probably sounded more acceptable three or four generations ago than it does now; language commentator William Safire still recommended its use in 1982.

In southern England people began saying something like an't I? in the late 17th century, pronounced ahnt. Because the southern English drop their rs, they later started spelling this as aren't I, with no difference in pronunciation. They preferred to use an unrelated word whose written form was familiar to them and whose pronunciation was the same.

When American r-keepers began noticing this in British writing at the beginning of the 20th century, it sounded crazy to them to have an r there. It made no sense at all, because there was no connection with the word are. So aren't I attracted considerable criticism. Nonetheless, it has gained acceptance over time, and now most Americans use it, since it's the only contracted form available to them that doesn't involve ain't.

Nowadays you'll find contradictory opinions on the acceptability of aren't I in writing, and particularly in formal writing. If you want to avoid controversy, stick to am I not? in writing. (The advice might differ if you're writing in Standard Scottish English, but I'm not qualified to comment on this.)

In speech and in writing meant to remain close to speech, there is a danger, alluded to in the comments, that am I not? will sound excessively stuffy and formal. In this case, aren't I? may be preferable, at least in England and North America.