It's time,It's high time
These are followed by past simple or continuous ,though the time reffered to is unreal.
It's time we left.
It's high time I was going.
I'd rather is followed by past verb forms in the same way as wishes about the present.It express preference about axtions.
I'd rather you didnt smoke here.
I'd rather is used with normal verb forms when comparing nouns or phrases
I'd rather be a sailor than a soldier.
Suppose, imagine
Understood conditions
The conditional part of these sentences is often understood but not stated.
Imagine we won the pools!
Suppose someone told you that I was a spy!
Imagine we'd never met! (we have met)
As with conditional sentences, if the event referred to is a real possibility, rather
than imaginary, a present verb form is possible:
Suppose it starts raining, what'll we do?
as if.as though
Real and unreal
The verb form here depends on whether the situation is true or unreal.
You look as if you're having second thoughts. (True. He is having second
thoughts.)
He acts as if he were in charge. (Unreal. He isn't in charge.)
/ feel as if an express train had hit me. (It didn't hit me.)
Note however, that the more colloquial like does not require this verb form
change. Compare:
You look like you've just seen a ghost
You look as if you'd just seen a ghost.
