First, here's a material that made me keep thinking about this issue in the first place.
- I feel as if I had known you all my life.
I haven't known you for that much, but I'm really comfortable with you like we are old friends.
- I feel as if I have known you all my life.
My one of old friends asked me how long we have known each other, and I'm guessing but I'm not sure whether when I was 3 or 4 that we first met. So, I'm saying like "I feel as if I have known you all my life."
I'd like to know the difference and use in exact situation. I'd really appreciate if you could help me.