Linguists are always taken aback by the overwhelmingly negative and sometimes virulently expressed reaction they get when stating something that every linguist believes (and linguists do not agree on everything!) in a rather uncomplicated way: Every dialect has a grammar.
“Every dialect has a grammar” does not mean “everything is relative, and let’s throw away all the dictionaries, and no one should go to school anymore, and I should be able to wear a bath towel to a job interview if I damn well please.” What it means is that all dialects, from the very fanciest to the ones held in lowest esteem, are rule-governed systems. Here are three examples from three different commonly disparaged dialects that illustrate how dialects have grammar.
She discusses Appalachian a– prefixing (“He was a-huntin'”), Southern liketa (“I liketa had a heart attack”), and African-American “stressed BIN,” which “is like a remote past tense, something that Standard English lacks a simple marker for.” Her approach is summed up in this fine paragraph:
People who speak this dialect don’t learn these rules from a book. They know them implicitly, even if they can’t describe them, the same way you know “I gave him a dollar” sounds good but “I donated him a dollar” sounds bad (even if you’ve never heard of linguistic argument structure). Their use of the dialect is not whimsical and random, but governed by those rules. Someone who doesn’t follow those rules, e.g., in a hamfisted attempt to mock the dialect, can be said to be speaking ungrammatical Appalachian English.
To write well and clearly about such touchy and ill-understood matters is a rare gift, and I hope a lot of people read and assimilate what she has to say.