Eugene and I think fairly similarly in matters of language, and I don't disagree with anything he's said so far. However, I want to make a more radical statement. Perhaps Eugene agrees with it, but I want to express it more nakedly. There is no such thing as the English language. Every person speaks slightly differently, understands a slightly different set of words, uses words slightly differently. When we say that a set of people "speaks English," this is a sloppy shorthand that means that when each of them speaks the way he normally speaks, the other people in the set can mostly understand what he's saying, and the meaning he's trying to convey is more or less the meaning they get. It's just an empirical statement about the degree of overlap between each person's "language."

This is all well and good, and we can keep using the shorthand of talking about "speaking English" for most purposes. Where the shorthand reveals its sloppiness, though, is when we see different people using different forms, possibly mutually incomprehensible forms, and say that one of them is "right."

But whenever we say that something is "right," we have to know what it's right for. "Right" can be meant either (1) as "proper to achieve a particular goal" or (2) as "inherently good." Now (2) seems implausible to me. Because when different people are speaking mutually incomprehensibly, this is as if one were speaking German and the other were speaking Spanish. Nothing inherently wrong with that. If these different people are speaking differently than each other but they can still understand each other, it's like a German speaker and a Spanish speaker who each understand both German and Spanish -- like when my father talks to me in Russian and I answer back in English. Nothing inherently wrong with that either. So the only way I can understand "right," in matters of language, is in the functional sense -- "proper to achieve a particular goal."

So to say that a usage is "right" or "wrong," you have to specify what goal you want to achieve. If I'm living in the inner city and my goal is to blend in, talking like a college professor is incorrect. Speaking African American Vernacular English (as the kids are saying these days) may be correct, though perhaps not if I'm white, and perhaps not if I seem like an outsider. Likewise, if my goal is to persuade people in the inner city, talking like a college professor may be incorrect -- just as it's incorrect to use a libertarian argument in support of policy if you're talking to a Marxist. On the other hand, if I think talking like a college professor will give me an air of authority that will make people do what I say, then talking like a college professor may well be correct. If I'm trying to get a job at a prestigious New York law firm, speaking Southern American English may be incorrect; but it can be correct if I have a radio talk show in Alabama and want to get my ratings up.

These are all different languages -- not "correct" and "incorrect" versions of some mass of dialects we sloppily label "English" -- and any one of them might be appropriate to know for a particular social situation. To say that a particular usage is "right" -- without, at least implicitly, having a "right for what?" in mind -- is like saying that a particular government program is "effective" without specifying a criterion of effectiveness.

But ah, one may validly ask, what do you teach your kids? What should we teach in schools?

In the first place, our kids should learn that with language -- like with all other tasks -- you should use the tools appropriate for what you're trying to do. Just as people might learn Spanish if they want to communicate with (what we might sloppily call) "Spanish speakers," they might learn Cajun English if they need to do social work in the bayou.

In the second place, we should usually spend most of our time teaching our kids to talk like rich and educated people in the United States. Not because that dialect is better, but because our kids will tend to be more materially successful in life if they know how to speak that dialect, and that's part of what most of us want for our kids. This is classist and elitist, and we might as well admit it; our kids should learn the dialect of the elite class, no matter how irrational it is, so they, too, can someday join that elite class. (Even if you would like to overthrow that elite class, wouldn't it be more effective to have a mole working on the inside?)

Thus, we can say "ain't" is "incorrect" for the simple reason that it'll make people less likely to give you high-paying jobs and positions of power -- assuming that you want those high-paying jobs or positions of power. Nonetheless, someone who knows many different versions of (so-called) "English" for many different social situations -- even if he doesn't know any of the (so-called) "foreign" languages -- is a true polyglot.