Judging language is tough, especially for English, which has no governing body. It's reasonably to allow "they" as a gender-neutral third person pronoun, both because of its ubiquity and because there is no better way to express that idea.
The problem then is figuring out which mistakes have been used frequently enough for long enough to be "acceptable." If the President of the U.S.A., while addressing the nation, used "ain't" or a non-literal double negative ("I don't see no problem with the economy"), can we say for sure he made a grammatical error?
The example in the first paragraph seems to hint that we can't ever really call something a grammatical error since there's no formal grammar for the language in question. However, the example in the second paragraph most certainly screams "GRAMMAR ERROR!" How do we rectify these two notions?
The problem then is figuring out which mistakes have been used frequently enough for long enough to be "acceptable." If the President of the U.S.A., while addressing the nation, used "ain't" or a non-literal double negative ("I don't see no problem with the economy"), can we say for sure he made a grammatical error?
The example in the first paragraph seems to hint that we can't ever really call something a grammatical error since there's no formal grammar for the language in question. However, the example in the second paragraph most certainly screams "GRAMMAR ERROR!" How do we rectify these two notions?