Did she use to or Did she used to?

 

Dr. Irvin Yalom has answered my question about why he wrote "Did she used to..." in his The Schopenhauer Cure. The correct form is "Did she use to..?" and the answer to the "error" is a phonetical one: The sound of the "t" blends with "use" to make it sound "used" and inadvertedly people fall into this grammatical ditch. A liaison that may sound far-fetched, but which is not. Try it. 

This answer does satisfy me.  And I thank Dr. Yalom for his quick reply.