I was taught to use past tense after the expression "as if" as in "he behaves as if he was a fool" (or past perfect as in "he behaved as if he had been a fool"). But so many times I see people writing both the verbs in the same tense (e.g. he behaves as if he IS a fool" - not sure it's right) and I don't have an idea when to use what. So could anyone please explain me when I should use "as if IS" and when "as if were" (If the main verb is in the same tense in the both, present simple I suppose).
Thanks in advance.
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'As if' is a part of one of those remnants of the subjunctive for hypothetical situations, Mav, so if you wish to write carefully:

'He behaves as if he were a fool.' (timeless)
'He is behaving as if he were a fool.' (present)
'He behaved as if he had been a fool.' (past)

The truth of the matter is that we see more and more an admixture:

'He behaves as if he was a fool.'
'He is behaving as if he is a fool.'
'He behaved as if he was a fool.'
'He behaves as if he is going to be appointed a fool'.

Other comments?
Ohhh, yessss.....I forgot to write "as if he WERE".... my bad.
Are the 'admixtures' grammatically correct?

Because I just found a definition of 'nausea' of Cambridge and it says: 'when you feel as if you are going to vomit'.
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Well, that is a more authoritative reference than your reference from a moderator's use. As I say, we see a lot of them, and I probably say them. But if I were writing a paper, I would change the 'are' to 'were'.
But is it grammatical? I
f I write it in a test will the teacher take off points?
Frankly, I think it depends upon the teacher.
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Mr.M. ,
I simply sometimes have a sentence and a verb is missing. I will bring the simplest example:
"He acted as if he __ crazy". And usually the sentences are much longer and it's important to be as accurate as possible.
What is actually the difference? If I put there "were" it would be "more grammatical" or it's just a matter of preference?
Thanks in advance.
"He acted as if he __ crazy".

I consider 'were' the only correct answer on this test. It is 'more grammatical'.
Careful, Mr. Mic. It's not "correct"; it's "standard"! Emotion: smile
(You never know when the 'terminology police' are lurking about.)
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