use of the phrase "What if"

[Sophie]

A friend of mine asks me about the use of the phrase "what if", but I don't know clearly about it. So could you please clarify this problem so that both of us can improve our knowledge.

Thank you in advance.
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On earth there is nothing great but man, in man there is nothing great but mind.

[*Vi*]

Hello again Sophie,

We use "What if" to suppose something, to take something as an assumption.

Ex: What if I have an accident and die? Life is too short, we ought to enjoy it to its most.
What if he isn't there? Should I leave a message?

Hope it helps,

Vi

[Sophie]

So we just use simple present after what if?
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On earth there is nothing great but man, in man there is nothing great but mind.

[*Vi*]

Not actually, I've seen other uses.

Ex: What if she called but we were out?
What if he hasn't found the address?

I don't see any problem using other verb tenses with it. Of course it sounds better with present or past,
since present gives an idea of future too and past refers to actions that have been concluded.

Corrections are welcome.

[Yankee]

Hi Sophie

An IF sentence usually contains two halves: a possible/probable/theoretical condition (in the IF-half of the sentence), and then the other half of the IF sentence states a result of the condition being fulfilled.

A sentence that begins with "what if" basically presents a condition and asks what a (or the) result will be/would be/would have been if that condition is/were/had been fulfilled. In other words, "what" basically asks for the other half of the IF-sentence. Here are some examples:

Q: What if he doesn't agree to do it?
A: Then we will just have to do it without him.

Q: What if you won a thousand dollars?
A: First I would treat myself to a gourmet dinner, and then I would spend the rest of the money on my kids.

Q: What if Sophie had not posted this question?
A: Then Amy would not have posted this reply.
.

[Sophie]

Thank you very much.
Tomorrow I'll explain this for my friend. I'm sure she'll be very happy, like how I feel at the moment.
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On earth there is nothing great but man, in man there is nothing great but mind.