if 3: special structures with past tenses and would

If I knew her name, I would tell you.
What would you do if you lost your job?
1 unreal situations
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.
2 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 (/-clause (even though the meaning is present or future), and would + infinitive (without to) in the other part of the sentence.
If I knew her name, I would tell you. (not If I know …)
(NOT If I would know …) (NOT … I will tell you.)
She would be perfectly happy if she had a car.
What would you do if you lost your job?
This structure can make suggestions sound less definite, and so more polite. It would be nice if you helped me a bit with the housework.
Would it be all right if I came round about seven tomorrow?
3 would, should
and
‘d
After I and we, should can be used with the same meaning as would. (Would is more common in modern English; should is rare in AmE.)
If I knew her name, I should tell you.
If I married you, we should both be unhappy.
We use’d as a contraction (see contractions).
We’d get up earlier if there was a good reason to.
For I should . . . meaning ‘I advise you to . . .’, see if I were you.2.
For would in the if-clause, see if 7: other structures found in spoken English.
For should in the //-clause, see if 6: other points.1.
4 if I were
etc
We often use were instead of was after if. This is common in both formal and informal styles. In a formal style were 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’ (see subjunctive).
If I were rich, I would spend all my time travelling.
If my nose were a little shorter I’d be quite pretty.
For the expression If I were you . . ., see if I were you.
5 ordinary tense-use or special tense-use?
If I come
or
if I camel
The difference between, for example, if I come and if I came 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. Compare:
– If I become President, I’ll… (said by a candidate in an election)
If I became President, I’d … (said by a schoolboy)
– If I win this race, Til…
(said by the fastest runner)
If I won this race, I’d … (said by the slowest runner)
– Will it be all right if I bring a friend? (direct request)
Would it be all right if I brought a friend? (less direct, more polite)
6 could
and
might
We can use could to mean ‘would be able to’ and might to mean ‘would perhaps’ or ‘would possibly’. »
If I had another Ј500, I could buy a car.
If you asked me nicely, I might get you a drink.
For other cases where a past tense has a present or future meaning, see past verb form with present or future meaning.
For if only, see if only.