If…should; if…happen to

We can suggest that something is unlikely by using should in the if-clause. Note that would cannot be used instead of should.

If you should meet Peter, tell him  that he owes me $50. (You are not very likely to meet Peter, but if you do tell him that he owes me $50.)

If … happen to has similar meaning.

If I happen to finish early, I will give you a ring.

Should and happen to can be used together.

If you should happen to meet Alice, give her my love. OR If you should meet Alice, give her my love. OR If you happen to meet Alice, give her my love.

When the if-clause contains should or happen to, we do not normally use would in the result clause.

If she should be late, we will start without her. (NOT If she should be late, we would start without her.)

If … was / were to

This is another structure used to talk about unreal or imaginary future events.

If dad was to come in now, we would be in real trouble. (= If dad came in now, we would be in real trouble.)

If I were to lose my job, I would be begging now.

Leaving out if

In a conversational style, if is sometimes left out at the beginning of a sentence.

You do it again, and I will kick your teeth in. (= If you do it again, I will kick your teeth in.)