I find that shocking!Quirk says this:
These are preferred in BrE and AmE:
He didn't use to smoke.
He didn't used to smoke.
That is more in line with my expectations.The construction did . . . use to is preferred to other constructions in both AmE and BrE.
The spelling did. . . used to, however, is often regarded as nonstandard.
And you are a professional writer who is 'a safe bet for what reads well in (American) English'.;-)I admit, I used to mess this up a lot because I type what I hear in my head, and "used to" sounds like "use to" but I've always had it corrected by others when I did.
I am not sure that Quirk is completely right to say that didn't used is preferred in BrE; it exists, but I think its status is more questionable than that. But then again, who am I to disagree.... ;-)
I am not shocked that people make the mistake. I am shocked that a respected book lists what I consider to be an error as preferred.
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