From ‘An Irish Childhood in England: 1951’ by Eavan Boland (full poem on my Tumblr):
let the world I knew become the space
between the words that I had by heart
and all the other speech that always was
becoming the language of the country that
I came to in nineteen fifty-one:
barely-gelled, a freckled six-year-old,
overdressed and sick on the plane,
when all of England to an Irish child
was nothing more than what you’d lost and how:
was the teacher in the London convent who,
when I produced “I amn’t” in the classroom
turned and said—“You’re not in Ireland now.”
I grew up in Ireland using expressions and grammatical constructions that I took to be normal English, only to discover years later that what counts as normal in language usage can be highly dependent on geography and dialect. I amn’t sure when I realised it, but amn’t is an example of this.
Standard English has an array of forms of the verb be for various persons and tenses with a negative particle (n’t) affixed: isn’t, wasn’t, aren’t, weren’t. But there’s a curious gap. In the tag question I’m next, ___ I?, the usual form is the unsystematic am I not or the irregular aren’t I (irregular because we don’t say *I are). Why not amn’t?