Didn't use/did use to not didn't used to/did used to

[Abraid2]

I didn't use to swim

I did use to swim

NOT

I didn't used to swim

I did used to swim.

You wouldn't say :

I did finished cakes, or
I didn't made that.

Would you?!

When you are using an auxiliary verb you follow with an infinitive.

"When you are using an auxiliary verb you follow with an infinitive."

Unless you are forming the present continuous, passive, present perfect, past perfect, past continuous etc etc.

You wouldn't find many examples of "I did use to..." either, unless the "did" is emphatic stress.

It is often used as emphasis, yes.

Take point about change of tense

Should be I USED NOT TO SWIM

If you are being extremely proper, but willing to sound a little dated.

I'd say "I usen't to" but then I'm Irish...

I love usen't to. Elegant,