We use special structures with if when we are talking about unreal situations--things that will probably not happen, situations that are untrue or imaginary, and similar ideas. In these cases, we use past tenses and would to 'distance' our language from reality.
1. if + past; would + infinitive without to
1. if + past; would + infinitive without to
To talk about unreal or improbable situations now or in the future, we use a past tense in the if-clause, and would+infinitive in the other part of the sentence.
If I knew the reason, I would tell you.( Not if I know)
2. if+past perfect; would have+past participle
This structure means past situations that did not happen.
If he'd run a bit fast, he could have won.
3. the difference between ordinary tense-use and special tense-use
Take if I come and if I came for example, the difference is not necessarily a difference of time. They can both refer to the future. But the past tense suggests that a future situation is impossible, imaginary or less probable.
If I become President, I'll…(said by a candidate in an election)
If I became President, I'd…(said by a schoolboy)
4. if I were
Usually, we use were instead of was after if.
5. could and might
could: would be able to
might: would perhaps or would possibly
4. if I were
Usually, we use were instead of was after if.
5. could and might
could: would be able to
might: would perhaps or would possibly
