Using 'soon' for past occurrences

I understand (and please correct me if I am wrong) that 'soon' simply means 'a short period of time'. With that in mind, I would like to relate a conversation I recently had with my wife.

"I gave the baby her medicine just before you came home," my wife told me. "How soon before I came home, did you give the baby her medicine?" I asked her in response.

What I meant to ask was, what was that short period of time which had elapsed between these two events. According to her, this is incorrect because 'soon' can only refer to something which will occur in the future.

Which one of us is correct?

Solution 1:

This is a pretty common usage, speaking as a non-expert british-english native speaker. I don't know if it is grammatically correct but in day-to-day usage no one would question it.

Soon does generally refer to a small amount of time between a reference time/event and a later time/event. The reference time/event is often implicitly now or implicit via the context.

The train will arrive soon [after now].

How soon [after now] will the train arrive?

It will be here very soon [after now].

But the reference time or event can be in the past or future, and the construction can be switched around somewhat.

The train arrived soon after he left her.

How soon [after he left her] did the train arrive?

Very soon after he left her the train arrived or It arrived very soon [after he left her]

or the future

How soon after the meal will you serve the pudding?

vs the past

How soon after the meal did you serve the pudding?

Both fine.

In many instances (as below) the noun phrase a while can be read as the opposite or a negation of soon.

How soon after the meal will you serve the pudding?

A while. If it is served too soon no one will eat it.