Q: I have a friend who uses the construction “Did you …?” where I would use “Do you …?” For example, if I were driving her home, she might say, “Did you want to come in?” This always makes me feel as if I’d invited myself in. Is it simply my own foible, or is there an actual grammar/usage reason behind my reaction?
A: I’ve noticed this too. For example, a barista at Starbucks might ask, “Did you want a grande or a vente?”
In effect, the barista is using the auxiliary verb “do” in the past tense (“did”), even though the present tense is implied.
It’s analogous to a salesclerk’s saying “Was that all?” (past tense) or “Will that be all?” (future) or “Would that be all?” (conditional) instead of the present-tense “Is that all?”
Why do people do this? When relatively insignificant verbs or auxiliaries are involved, some people seem to feel that the present tense (“Do you want …”) is too direct or blunt, and that an oblique, roundabout approach is somehow more polite.
I wouldn’t read anything into your friend’s usage – for example, that it’s not HER idea to invite you in. This is probably just her way of saying “Do you …?”