First, here's a material that made me keep thinking about this issue in the first place.
http://www.grammaring.com/as-if-as-though
She acted as if she didn't know me.
It was the first time that I'd seen her since I was in elemantary school.(and now I'm 26). A couple of days ago, when I met her, she acted as if she didn't know me. I think she didn't remember me.
She acted as if she hadn't known me.
I broke up with her a couple of weeks ago, and when I met her yesterday, she acted as if she hadn't known me. She definitely knew who I am, but pretended as if he hadn't known me because she didn't want to talk to me.
Is it right that I make a situation like that with each sentence? I hope this try will be concerned not only for me, but also for other English learners.
Best Answer
We tend not to speak of having known someone unless there’s a fixed period of time, either explicitly mentioned or implied by the situation (e.g. the person is deceased).
With that in mind, I would switch your two usages to describe the other scenarios, with slight alteration:
In this case, there’s a specific timeframe in which knowing occurred, which has since ended.
This is the common use of the phrase. We think we either know someone or we don’t. It’s like a light switch. She acted like the light was off; she acted like she didn’t know you.
Another common way English speakers would discuss something like this is to say “she acted like we hadn’t met” or “she acted like we’d never met”. These use “met” in the sense that you meet someone and from that point forward you know that person.