We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
Somewhat related is You and I versus you and me. It's easy to sort that one out without making any reference to grammatical terms. Just mentally simplify the sentence to one person and it clarifies itself. Eg, "You and me should have lunch." "Me should have lunch"? Naw. So it's "You and I..."
Sometimes? How about always? I know of almost no speaker on either side of the Atlantic who would routinely say it is I rather than it's me unless they were speaking in a quite deliberately affected manner.
"Just mentally simplify the sentence to one person and it clarifies itself. Eg, 'You and me should have lunch.' 'Me should have lunch'? Naw. So it's 'You and I...'"
This is not a proof that you and me should have lunch is wrong. It's only a proof that me should have lunch is not right (and something no speaker except a toddler is ever likely to say, including the millions of speakers who would say you and me should have lunch).
"C'est moi, c'est moi, I'm forced to admit". Actually, I still would, given the circumstances, say "it is I". But then I'll also use the "it is not so... as..." for a negative statement whereas other will use " it is not as ... as...".
Usage changes. I still use "It is I," but I adopted that as a bit of an affectation forty years ago in college. It's archaic now. Adherence to an old rule is a social signifier - that you received such-and-such an upbringing/education. It can no longer claim correctness.
We can see this best by looking at other languages. If we find an unvisited tribe and learn its language, we regard the language spoken by the native speakers as correct. Running into a couple of old guys who try to bend our ear that the word should be t'innu, not t'inn, because it comes from a group of double-consonant words that always take a "u," because that's what they were taught at the best campfires when they were young, we would simply ignore them.
Native speakers of a language use the language correctly. There is no other definition of a language that can hold up under examination. Anything beyond that is a social or cultural statement, not a linguistic one.
That said, one should teach children the usage most likely to benefit them as adults. Awareness of one's usage teaches other good habits.
Assistant Village Idiot
Some of us refuse to recognize the death of the adverb.
As a personal decision, you should refuse. There is added clarity, and any slowing of language change makes us better able to keep in touch with earlier eras by understanding them. You should also teach this to your children and grandchildren. But that's not the same thing as claiming correctness.
Assistant Village Idiot
"There is added clarity"
Do we muddle the meaning of the adjective fast because it doesn't usually become fastly as an adverb?
"Me and Jim went to the store" sounds informal and colloquial, either a little jocular or a little uneducated. "Between you and I" sounds like an ignorant hypercorrection, a betrayal of class anxiety.
I say "It is I" if I'm being formal and "it's me" if not. That's what a command of idiom is. In a business letter, for instance, I'd say "It is I who should be paying this bill, not you." If I startled someone in the dark, I'd say, "Don't worry, it's just me." If I said, "Fear not, it is only I," my listener probably would assume I was jokingly striking a pose from an old-fashioned play.