1. conditional and if-sentences
(1)

2. real conditions (first conditional)
if + present simple + will / won't (do)
This shows the results in the future of a real situation, with possible or likely results.
If you eat all the ice-cream, you'll be sick!

3. other variants If can also be followed by can / can't, present perfect
(to emphasize completion)
going to, present continuous with future meaning.
If you can't answer Exercise 1, you won 't be able to do Exercise 2.
If you've finished washing the floor, I’ll help you clean the kitchen.
If you're going to buy a car, I’ll Iend you some of the money
If you're going to the shops, I’ll come with you!

4. The second clause can contain could requests, be able to, can, going to, imperative, had better, could and might etc
If I give you the money could you get me same stamps?
If you've finished washing the floor, you can start cleaning the kitchen.
If it rains this afternoon, we're going to stay in and watch some DVDs.
If you're going to buy a car, make sure you get it checked by a garage.
If you're going to the shops, you'd better take same money!
If Cole scores now, that could be the end of the match!

5. future results: if clauses with will
There are some if-sentences that describe the possible results of an offer.
In these sentences, will is used in the if-clause.
I’ll talk to your teacher, if that will stop you worrying so much

6. In some if-sentences, if is followed by emphasized will, meaning 'insist on', or won't meaning 'refuse to’
If you will wear such thin clothes, of course you'll feel cold!
If you won't listen to common sense, there's no point my talking to you.

7. If can be followed by will and would as polite request forms.
If you'll just wait here, I’ll tell Mr. Brown that you've arrived
If you'd just fill in this form, I'II check the details

8. unreal conditions (second conditional)
if + past simple + would (do)
This shows the results which would follow from an imaginary situation, with impossible or unlikely results.
If the Earth didn't have a Moon, there wouldn't be any tides.

9. Could and might are often used instead of would, as are other modals.
If we all worked together, we could solve the problem faster

10. The difference between real and unreal may be a matter of speaker choice and context.
A. If you buy a bike, you'll get a lot fitter.
(You are really thinking of buying one - perhaps we are in the bike shop.)
B. If you bought a bike, you'd get a lot fitter.
(We are only discussing possibilities.)

11. impossible past conditions (third conditional)
if + past perfect + would have (done) / (passive would have been done)
Used for the results which would follow from an imaginary past situation.
As we cannot change the past, this is an impossible condition.
Passive forms are common.
If the ship had had more lifeboats, more passengers would have been saved.
If the ship hadn't hit an iceberg, it wouldn't have sunk.
If another ship hadn't arrived soon afterwards, none of the passengers would have been saved.

12. Could have and might have are often used instead of would have, as are other modals.
If the ship had been travelling more slowly, it might have avoided the iceberg.

13. mixed conditions if + past perfect + would (do)
Used for an imagined or actual event in the past with a result in the present.
If she had worn her seat-belt, she would still be alive.
If you hadn't given me a lift, I'd probably still be at the station!

14. if + past simple + would have (done)
Used for a present state which has influenced past events.
If you weren't so lazy, you'd have finished your work by now
If she was better-qualified, she would have gat the job.

15. b Make a back-up copy of your work or you'll lose it. You won't__
Complete each sentence giving computer advice using an if-condition, so that it has the same meaning as the first sentence.
a Don't press that button on the keyboard, or you'll lose what you've written.
If__
b Make a back-up copy of your work or you'll lose it.
You won't__
c You need virus protection to avoid having problems with your computer.
If you don't__
d Sitting too long at the computer will make your back and arms ache.
Your

16. e Don't turn off the computer before closing all programs, or you could have problems.
f You'll lose your work unless you save it before closing the word-processing program.
If__
g You can save a lot of time by learning the keyboard short cuts.
h Running too many programs at the same time will probably make the computer crash.
The computer will___

17. answers
a ... you press that button on the keyboard, you'll lose what you've written b… lose your work if you make a back-up copy. c have virus protection you'll have problems with your computer. d ... back and arms will ache if you sit too long at the computer. e ... could have problems if you turn off the computer before closing all programs. f ... you don't save your work before closing the word processing program, you'll lose it. g ... you learn the keyboard short cuts, you can save a lot of time. h ... probably crash if you run too many programs at the same time

18. If all the people on Earth a (disappear)__ tomorrow, nature b (begin)__ to reclaim the planet. For a start, if people no longer c (pollute)__the atmosphere, the air d (soon become)__ clean again. If there e (be)__ no people to maintain buildings, they f (soon begin)__ to decay, but more solid parts g (take) __thousands of years to disappear. In general, if the 6.5 billion humans no longer h (compete)__with other species on Earth, most species i (benefit)__.For example, if humans no longer j (catch) __fish, the numbers of fish worldwide k (eventually increase) __. However, if humans I (vanish)__ from the Earth, endangered species of animals m (not necessarily recover) __as some are already too few in number.

19. Some endangered species n (have)__greater difficulty surviving if no humans o (take)__the trouble to protect them from other species. Even if we no longer p (poison) __the planet, several decades q (go by)__ before all dangerous chemicals r (disappear)__. And even if the burning of fossil fuels s (cease)__tomorrow, the oceans t (not absorb) __all the CO2 in the atmosphere for thousands of years. In the end, though, if alien visitors u (land) __on the Earth in 100,000 years time, they v (find) __no signs that an advanced civilization had ever lived here.

20. Answers
a disappeared b would begin c polluted d would soon become e were f would soon begin g would take h competed j would benefit j caught k would eventually increase l vanished m would not necessarily recover n would have o took p poisoned q would go by r disappeared s ceased t would not absorb u landed v would find