Conditional Sentences

If… should;  if…. happen to

We can suggest that something is unlikely, or not particularly probable by using should (not would) in the if-clause.

If you should meet peter, tell him he owes me a letter.

If… happen to has similar meaning

If you happen to pass a supermarket perhaps you could get some eggs.
Should and happen to can be used together.
If you should happen to finish early, give me a ring.

Would is not normally used in the main clause in the structures.

If he should be late we will have to start without him. (NOT …we would have to start without him)

If …was/were to

this is another way of talking about unreal or imaginary future events.

If the boss was/were to come in now, we would be in real trouble.(=if the boss came…)
What would we do if I was/were to lose my job?

It can be used to make a suggestion sound less direct and so more polite

If you were to move your chair a bit, we could all sit down.

This structure is not used with state verbs.

If knew her name, I would tell you (NOT   I were to know her name...) 

If it was/were

This structure is used to say that one particular event or situation changes everything.

If it wasn’t/weren’t for his wife’s money, he would never be a director (=without his wife’s money)

If it wasn’t /weren’t for the children, we would not have anything to talk about.

To talk about the pas past we use if it had not been for.

If it had not been for your help, I don’t know what I would have done.
But for can be used to mean if it were not for or if it had not been for.
But for your help, I don’t know what I would have done. 

Leaving out if

conversational structures

If it sometimes left out at the beginning of a sentence in a conversational style, especially when the speaker is making conditions or threats.

If you want to get in you pay like everyone else. (=if you want…)
You touch me again, I will kick your teeth in. 

Formal inversion structures

In formal and literary styles, if can be dropped and an auxiliary verb put before the subject. This happens with were, had and should and very rarely with other auxiliary verbs.
Were she my daughter, I would buy her this frock.

Had I realized what you meant, I wouldn’t do so.

Should you need further clarification, please do not hesitate to contact us.

However in this structure, negatives are not contracted.

Had we not changed our reservations we should all have been killed in the crash (NOT  hadn’t we changed...)  

Extra negative

An extra not is sometimes put into if-clauses after expressions suggesting doubt or uncertainty.

I wonder if we shouldn’t ask the doctor to look at Mary (=I wonder if we should ask…)
I wouldn’t be surprised if she didn’t get married soon (=if she got married soon…) 

Parallel structures; would… would

Conditional would is sometimes used in both clauses of an if-sentence. This is very informal and is not usually written. It is common in spoken American English.

It would be better if they would tell everybody in advance.
How would we feel if this would happen to our family? 

Parallel structures; ‘d have… ‘d have

In informal spoken English if-clauses referring to the past are sometimes contracted with‘d have. This is frequently considered incorrect but happens quite often in educated people’s speech. It is not normally written.

If I’d have known I’d have told you.
It would have been funny if she’d have recognized him.

Instead of the contracted ‘d full forms are sometimes used for emphasis or in negatives. Both had and would occur.

We would never have met if he hadn’t have crashed into my car.
If you wouldn’t have phones her we would never have found out what was happening. 

Elliptical structures

In a formal style subject + be is sometimes left out after if.

If in doubt ask for help. (=if you are in doubt…)
If about to go on a long journey, try to have a good night’s sleep.

See Conditional Sentences - Other Points II