Sentence 4 sounds archaic to my AmE ears. The rest are fine. I think most Americans would write I didn't used to smoke and Did he used to swear. Even though using the past participle is not logical, it matches the way we pronounce use to as "yoosstoo."
I used to run every morning. (Common)
I used not to smoke. (Formal)
I didn't use to smoke. (Common)
Used he to swear at you? (Formal)
Did he use to swear at you? (Common)
It's not just a matter of formality, but also whether "used" is seen as a lexical verb or an auxiliary one. Here's a run-down on the important points:
The aspectual verb "use" has no present tense, only infinitival and past forms, so although the form "use" appears to be a present tense form, it is in fact the plain (infinitive) form which is only used in negatives and with inversion:"He didn’t use to smoke"; "Did he use to smoke"?
There is the added complication that "use" can be a lexical verb or an auxiliary one, though the books tell us that many speakers treat it as a lexical one. I suspect that’s due to the unacceptability for many people of the auxiliary use found in %”Smoking usedn’t to be allowed” and %“Used he to smoke”?
Lexical Use (infinitival verb-form and do-support required in negatives and questions):
He used to smoke.
He didn’t use to smoke.
Did he use to smoke?
Auxiliary Use (past tense verb-form, no do-support required)
He used to smoke. %He usedn’t to smoke. %Used he to smoke?
Does That help?
Last edited by PaulMatthews; 07-Apr-2016 at 17:52.
That's why I marked it "%", meaning it is marginally acceptable, and then only in some dialects.
"He didn't used to smoke" is, as you say, not correct. The uncertainty with the spelling probably arises because "used to" is pronounced with a single /t/ and hence is homophonous with the "use to" in "he didn't use to smoke".
Last edited by PaulMatthews; 07-Apr-2016 at 18:22.
That's why I marked it "%", meaning it is marginally acceptable, and then only in some dialects..
I thought those percent signs were artifacts of some kind. If you use that symbol to mean "marginally acceptable", may I suggest you explain that in your text? I don't remember having seen it used that way before.