Page 271 - Practical English Usage 3ed - Michael Swan, Oxford

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if (6): other points 261 Ifabout to go on a longjourney, try to have a good night's sleep.
For more details of ellipsis (structures with words left out). see 177-182.
ifsoandifnot
After if, we can use so and not instead of repeating a whole clause.
Are you free? Ifso, let's go out for a meal. (= ... If you are free ...)
I might see you tomorrow. Ifnot, then it'll be Saturday. (= ... If I don't see
you tomorrow ...)
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 ifshe didn't get married soon. (= •.• if she got married soon:)
if...then
We sometimes construct sentences with if... then to emphasise that one thing depends on another.
Ifshe can't come to us, then we'll have to go and see her. if meaning 'even if'
We can use ifto mean 'even if (see 189.4).
I'll finish this job if it takes all night.
I wouldn't marry you if you were the last man in the world.
admitting facts with if
An if-clause can be used to admit a fact when giving a reason for it.
If I'm a bit sleepy, it's because I was up all night.
if meaning 'I'm saying this in case'
If-clauses are quite often used to explain the purpose of a remark - to suggest 'I'm saying this in case .. .'
There's some steak in the fridge ifyou're hUngry. Ifyou want to go home, Anne's got your car keys.
if meaning 'although'
In a formal style, ifcan be used with a similar meaning to although. This is common in the structure if+ adjective (with no verb). lfis not as definite as although; it can suggest that what is being talked about is a matter of opinion, or not very important.
His style, ifsimple, is pleasant to read.
The profits, ifa little lower than last year's, are still extremely healthy. The same kind of idea can be expressed with may ... but (see 342).
His style may be simple, but it is pleasant to read.
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