We use special tenses with if when we are talking about unreal situations – things that will probably not happen, and situations that are untrue or imaginary, past events that did not happen, and similar ideas. In these cases, we use would and past tenses to distance our language from reality.
Present and future situations
To talk about unreal or improbable situations now or in the future, we use a past tense in the if-clause (even though the meaning is present or future) and would + infinitive in the other part of the sentence.
If I knew her name I would tell her. (NOT if I know…) (NOT …I will tell you)
She would be happy if she had a car.
What would you do if you lost your job?
This structure can be used to make a suggestion sound less definite (for instance, if we want to be more polite).
It would be nice if you helped me a bit with the house work.
Would it be all right if I came round about seven tomorrow?
Would & should
After I and we, should can be used in British English with the same meaning as would.
If I knew her name I should tell you.
If we had a map we should be able to find the road.
We use‘d as a contraction
I’d get up earlier if there was an alarm clock.
If I were etc.
We often use were instead of was after if. This is common in both formal and informal styles. In formal style it is more common than was, and many people consider it more correct, especially in American English. The grammatical name for this use of were is subjunctive.
If I were rich, I would spend all my time traveling.
If my nose were a little shorter I would be quite pretty.
Note that were is not normally used instead of would be in polite requests.
We should be grateful if you would be so kind as to let us have your cheque as soon as possible (NOT …if you were so kind)
Special tense use and ordinary tense use compared
In conditional clauses, the difference between, for example, if I come and if I came is not a difference of time. They can both refer to the present or future; the past tense suggests the situation is less probable, or impossible or imaginary. Compare:
If I become president, I will… (said by a candidate in an election)
If I became president, I would… (said by a schoolboy)
Will it be all right if I bring a friend tonight (direct request)
Would it be all right if I brought a friend tonight (less direct, more polite request)
Unreal past situations
To talk about past situations that did not happen, we use a past perfect tense (had + past participle) in the if clause, and would have + past participle in the other part of the sentence
If Mark had asked me, I would have told him. (Mark did not ask)
(NOT if you would have asked me…)
(NOT if you asked me…)
(NOT …I had told you)
If you had worked harder, you would have passed your exam. (you have failed)
I would have been in bad trouble if Jane hadn’t helped me. (Jane helped)
Unrealized present and future possibilities
The same structure can sometimes be used specially in British English to talk about present and future situations which are no longer possible because of the way things have turned out.
If my mother had been alive, she would have been 80 next year. (Or if my mother were alive, she would be…)
It would have been nice to go to Australia this winter, but there is no way we can do it (or it would be nice…)
Could and might
In unreal conditional sentences we can use could to mean would be able to and might to mean `would perhaps’ or `would possibly’.
If I had another $5000, I could buy a new car.
If you asked me nicely I might get you a drink.
Could have, might have can be used in sentences about the past.
If he would run a bit faster, he could have won.
If I had not been so tired I might have realized what was happening.