[Grammar] As if/ As though when expressing an imaginary situation.

[saloom2]

Hello everyone,

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.

For instance,

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)

 

[englishhobby]

Ahmed is looking hard at him as if he knew him. ( He doesn't.)

Yes, both tense forms can be used with as if/as though, just like with if - for both real and uneal situations. Compare:
It looks as though it's going to rain. - a real situation: there are obvious signs of the coming rain.
He is looking at me as though he was going to kill me. - unreal situation (hopefully).

That's how I see it.

 

[saloom2]

Well, What about the past?

he was looking at the sky as though he noticed sth.(He did notice sth)
He was looking at the sky as though he had noticed sth. (Nothing)

Am i right?

 

[englishhobby]

Well, What about the past?

he was looking at the sky as though he noticed sth.(He did notice sth)
He was looking at the sky as though he had noticed sth. (Nothing)

Am i right?

I am not quite certain, but I think that doesn't work with this particular verb - to notice. "I had noticed" would be just the sequence of tenses for "he has noticed".