What makes something "grammatically incorrect"?

[guizot]

@jepflast

If instead the question is, “I have an error. Is it grammatical or something else?”, well, that’s a different question. Then we get into the definition of grammar and perhaps a discussion of other types of errors. I don’t think that was the OP’s intent. (But no doubt it would make for a good discussion.)

Yes, good point–I don’t think that was the OP’s intent, either. There is a difference between “grammatically incorrect” and ungrammatical.

[guizot]

@Exapno_Mapcase

I say “context is everything” a lot, and I get to say it again here. . .
So I disagree with guizot. We are discussing written language in this thread, and written language is a thing unto itself, a context that is distinct from spoken language even if they at times overlap.

I think I might say “context is everything” even more than you, albeit in a roundabout way, and I don’t think anything I said contradicts what you said.

But I think the context for “I’m doing well/good” is probably speech much more often than writing–at least in a context where people are going to be judging correctness of grammar.