Ain’t – First, a little history: Ain’t emerged in the 17th century. In the 18th and 19th centuries, it was even used by authors such as Jonathon Swift, Lord Byron, Charles Dickens and Anthony Trollope, even in portraying upper class characters.
Furthermore, would you say “I am not going to school today” or “I are not going to school today”? Of course, we say “I am” and not “I are.” Granted, we would say “I’m not going to school today” but we do in fact use “I are” when we flip the subject and the verb, as in, “I’m cute, aren’t I?”
“Ain’t” is a contraction of “am not.” Therefore, it is logical to say “I ain’t,” and this should be considered proper usage.
Alas, the prescriptivists (“grammar nazis”) have mysteriously taken a disliking to “ain’t,” and therefore it is considered improper. When Webster dictionary dared include “ain’t” in their 3rd edition (full name Webster’s Third New International Dictionary), the prescriptivists acted like the world was over.
Willn’t – Okay, I don’t actually know anyone who uses “willn’t,” but it has been used in everyday speech in Yorkshire, England.
The “proper” contraction for “will not” is, as we know, “won’t,” which, for modern English speakers, makes absolutely no sense. Why does the “ill” sound go away, to be replaced by “oh”? Our other contractions make sense. For example, “should not” becomes “shouldn’t,” “did not” becomes “didn’t,” etc. Contractions in English have a predictable pattern. But “won’t”? When I teach contractions, I have to just give my students this one, since there is no way for them to figure it out.
So where did “won’t” come from? To be fair, “won’t” actually does make sense in the context of the history of English. In Old English, “will” and “wol” were actually two variants of the same word. “Will” won out in the stand-alone contest and “won’t” won in the contractions category. The “standard” form of a language is really a matter of politics: however the elite speak becomes standard.
I still like “willn’t.”
Y’all – I am particularly fond of this one, and use it regularly. It is a contraction of “you all” and is predominantly used in southern states, where it was coined in the early 19th century.
We need the word “y’all.” After all, English has no second-person plural pronoun. (Say that 5 times fast!) In the first person, we have “I” which is singular, and “we” which is plural. In third person, we have “he” or “she” which are singular, and “they” which is plural. But in second person we just have “you.” How many people are there? No idea. That’s why we need “y’all.” That way “you” can be singular and “y’all” can be plural.
The Story of English in 100 Words, by David Crystal
The Lexicographer’s Dilemma, by Jack Lynch