I'm an old truck driver. Went to catholic grade school in the 50's. Learned early on that the abbreviated word "ain't" was a contraction for ( am I not ).
Was I taught error? Are modern definitions of the contraction more or less true then what I hold dear.
The reason I ask is because I was brought up short for pointing out the redundancy of using "I" with the contraction.
Another pet peeve is on our nations highways. " Buffalo an All America City "
Again I was taught that agreement in number is important. Error again????
Thanks for any light you wish to shed on these earth shattering questions.
FWIW, I too heard at some (much more recent) point that "ain't" is a contraction for "am not". The problem with that justification is that people use it for any pronoun, not just first-person singular.
Doesn't keep me from using it orally, though. "I ain't doin' that", that sort of thing.
You are both right that ain't was once a common contraction, with reasonable respect. It was a contraction of am not, or possibly are not. Its history is a bit complicated.
If it ain't broke, don't fix it.
I don't see much evidence that the pronoun I should or must be omitted when using ain't, but clearly there are some examples when it is. "Ain't doing that." omits the pronoun I. But I see this omission as similar to the understood pronoun in the adolescent exchange:
"Am not!"
"Are so!"
The disuse of ain't almost certainly did come from hypercorrection. Strong evidence of this hypercorrection is the abomination of "Aren't I?"
For a lengthy treatment of ain't you can read here:
Merriam-Webster's Dictionary of English Usage; ain't
As for your second question about agreement in number, I don't think I see how the Buffalo quote applies. Can you explain your question more fully?