Page 268 - Practical English Usage 3ed - Michael Swan, Oxford

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if (4): unreal past situations 259 If I had another £500, I could buy a car.
Ifyou asked me nicely, I might get you a drink.
For other cases where a past tense has a present or future meaning, see 426.
For ifonly, see 265.
if (4): unreal past situations
lfyou had worked harder, you would have passed your exam.
if + past perfect; would have + past participle
To talk about past situations that did not happen, we use a past perfect tense in the if-clause, and would have + past participle in the other part of the sentence.
IIyou had asked me, I would have told you.
(NOT /f}'6ft !tI8ftitl httve fI:SIeet1 me . ..)
(NOT /f}'6ft fI:SIeet1 me ...) (NOT ••• : had tBitl }'6ft:) Ilyou had worked harder, you would have passed your exam. I'd have been in bad trouble ifJane hadn't helped me.
could have . .. and might have ...
We can use could have + past participle to mean 'would have been able to .. .', and might have + past participle to mean 'would perhaps have ... ' or 'would possibly have .. .'.
If he'd run a bit faster, he could have won.
IfI hadn't been so tired, I might have realised what was happening.
present use: situations that are no longer possible
We sometimes use structures with would have . .. to talk about present and future situations which are no longer possible because of the way things have turned out.
It would have been nice to go to Australia this winter, but there's no way we can do it. (OR It would be nice .. .)
If my mother hadn't knocked my father off his bicycle thirty years ago, I wouldn't have been here now. (OR ••• I wouldn't be here now.)
if (S): if ... will
I'll give you £100 ifit will help you to go on holiday. IfAnn won't be here, we'd better cancel the meeting. I don't know if I'll be ready in time.
Ifyou will come this way .. .
Ifyou will eat so much .. .
We normally use a present tense with if(and most other conjunctions) to refer to the future (see 580).
I'll phone you ifI have time. (NOT ••• if>' will have time.) But in certain situations we use if... will.
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