Thingol, your argument suggests equal validity, in all situations–formal or un–for Standard English and Ebonics. Surely you see a difference? That’s the difference being discussed here. The debate on the nature and the origins and the social implications of that difference are for a different thread.
Yeah, but it’s also Standard English, where “used to could” is not. When people ask whether something is grammatically correct, it’s logical to infer that they mean within Standard English, otherwise anything anyone says could be called “correct” because it follows someone’s usage.
Jomo Mojo, I did miss the construction “didn’t use to,” but I do agree with Garner that it’s incorrect in that case, as well. If you’re not going to use the proper SFE phrase “used not to,” then “didn’t used to” is perfectly correct, though informal.
Pulykamell, I have great respect for the American Heritage people, but must disagree in this case: there is no expression “use to” in English, and the apparent logic of “didn’t use to” is misleading. “Used to” is an expression in itself, and is always connected to another verb, unlike some examples used in this thread.
Thingol, your authors are all writers of poetry and fiction. As such, they are using conventions of reported and figurative speech that do not need to be “correct.” I would venture that none of these talented and educated people would use the expression “used to could” in a legal document or an academic report.
Here is another site supporting the use of “use to” when combined with “did.” From the bottom of that page:
The grammar and usage books that I have at home agree.