As if/ As though when expressing an imaginary situation.
In my grammar book, it's written that as if/ as though can be used to express an imaginary situation, but I'm a bit confused with it because while reading some books, I found out they're used normally.In other words, the past tense express a past situation, not an imaginary one.
Ahmed is looking hard at him as if he knows him ( He knows him)
Ahmed is looking hard at him as if he knew him ( He don't)
I wish I had better English, but I work hard to improve it. I'm studying for IGCSE, so I'm only interested in BrE.