Objective Proficiency p 26. Conditionals. Grammar

When the if clause comes before the result clause, we usually separate the two clauses with a comma. When the result clause comes first, we do not use a comma:
E.g. If you share a car to work, you can save on energy
You can save on energy if you share a car to work

Zero conditional
if/ when + present simple, present simple
We use the zero conditional to talk about situations which are always true.
E.g. If I eat too much spicy food, I start to feel ill.
When I eat too much in the evening, I can't sleep at night. 

if/ when/ whenever + past simple, past simple
The past simple can also be used in conditional sentences to describe real situations in the past.
E.g. If I arrived late at the office, my boss used to get really angry.

First conditional
if + present simple, will/ going to/ may/ might/ can/ could/ shall/ should/ have to/ ought to  + infinitive/ imperative
We use the first conditional to talk about possible future situations and their probable results.
E.g. If you don't water the plant soon, it'll die.
If you don't water the plant soon, it could die.
We might prevent disaster if we change the way we live now.
If the people from Greenpeace call, tell them I'll call them back later.

if + should/happen to/ should happen to
We use this structure to make the event seem more unlikely or more of a chance possibility.
E.g. If you should see Davina, ask her whether she could look after the cats this weekend.
If I happen to see Mr Smith, I'll ask him for you.
If you should happen to miss the train, I could drive you there myself.

A more formal variation is to omit if and begin with should (inversion)
E.g. Should you wish to change your holiday arrangements, we will do all we can to help.
Should you require more assistance, please telephone. 
Should the drought /draʊt/ continue, many people will be forced to leave their villages.

Note
if can sometimes be followed by will, would or going to, for example when making polite requests or describing the result of a course of action.
E.g. If you would take a seat for a moment, I'll tell Mr Graydon you're here.
If it is going to be more profitable for the company, then I think we should do it.
I'll clean the house if you'll mow the lawn.


Second conditional
if + past simple/ past continuous, would/ might/ could + infinitive
We use the second conditional to talk about imaginary, unlikely or impossible situations in the present and future.
E.g.  If I had an extra pair of hands, then I could help you!
I might work harder if they paid me more.

If it wasn't/weren't for + noun
E.g. I think I'd be quite lonely if it wasn't/ weren't for my dog, Buster. (= if I didn't have)
If it weren't for my savings, I wouldn't be able to survive (= Thanks to my savings I can survive)

Were it not for + noun
E.g. Were it not for my dog, Buster, I think I'd be quite lonely.

if + were to + infinitive makes the event seem more unlikely.
E.g. If you were to walk in that direction for another thousand miles, you'd eventually arrive in Warsaw.

A more formal variation is to omit if and begin with were...to (inversion)
E.g. Were they to break the contract, we would of course take legal action.
Were you to go out in this weather, you'd be thoroughly soaked

Third conditional
if + past perfect, would/ might/ could/ should + perfect infinitive
We use the third conditional to speculate about how things might have been different in the past.
E.g. If you had been paying attention, you might have understood what I was saying. (= You weren't paying attention, so you didn't understand.)
A lot more people would have been trapped by the flood if there hadn't been a warning. 

If it hadn't been for + noun
E.g. If it hadn't been for your help, I wouldn't have been able to quit gambling. (= if I hadn't had)
If it hadn't been for that traffic jam on the motorway, we would have got here on time. (= Because of the traffic jam we arrived late.)

Had it not been for + noun
E.g. Had it not been for your help, I wouldn't have been able to quit gambling.

But for/ without 
E.g. But for your help, I wouldn't have been able to quit gambling.
He would have played but for a knee injury.
Without their help, Emma couldn't have overcome her problems.
You shouldn't take these pills without consulting your doctor.
 
A more formal variation is to omit if and begin with had (inversion)
E.g. Had she known about his criminal past, she would never have employed him.
Had I known there was going to be a storm, I would have stayed indoors. 
Had Charles Darwin not visited the Galapagos Islands, he might never have developed his theory of evolution. 
Had we not attended the meeting, we would have han no idea of the council's plans. (Note that not goes after the subject).

Mixed conditionals
if + past tense, might/ could/ should/ would + perfect infinitive
We use this structure for situations in the present which affect the past.
E.g. If I weren't so untidy, I wouldn't have lost your keys.
If I weren't so broke at the moment, I could have bought you something decent for your birthday.

if + past perfect, would/ might/ could + infinitive
We use this structure to speculate about how a different situation in the past might have had different results in the present.
E.g. If I had moved to California, I would be much richer today.
If you hadn't stayed up to watch the film last night, you wouldn't be so tired now

Other words and phrases that introduce conditionals
Providing (that)/provided (that)/  as/so long as/ on condition (that) are similar to only if. They are all emphatic forms emphasising a condition. 
E.g.  Providing that you have the money in your account, you can withdraw up to £100 a day.
You can have a pet provided that you promise to look after it properly.
We'll buy everything you produce, provided of course the price is right.
We'll go up to the mountains this weekend as long as the weather's okay. 
Applications for membership are accepted on condition that applicants are over 18.

Suppose / Supposing/ Imagine/ what if can be used instead of if, particularly in speech. They are used at the beginning of the sentence setting up the condition.
E.g. Suppose it rains tomorrow. What will we do?  
Suppose the price of oil tripled tomorrow. What do you think would happen?
Supposing you ran out of money, what would you do?
Supposing you had met the president, what would you have said?
Imagine you lost your job. Do you think you'd be able to find another?
Imagine you had missed the flight, what would you have done? 
What if the iceberg tipped over (fell), could the fishing boats have escaped?

If so/ not
E.g. Are you concerned about the environment? If so, you might be interested in joining Greenpeace.
Do you have the potential to be a concert pianist? If not, give yourself a break and do something else. (= If you don't have the potential)

Otherwise (= if...not)
E.g. You should have your air conditioner serviced, otherwise you'll waste a lot of energy.

Unless/ except when (= if...not)
E.g. Unless governments act now, the environment is really going to suffer.
I won't give a waiter a tip except when/ unless I get excellent service.

In the event of (= if something happens)
E.g. In the event of  the alarm sounding, visitors should leave the zoo by the nearest exit  

In case of + noun
E.g. In case of fire, leave the building by the nearest emergency exit.

In case (= as a precaution)
E.g. Take a coat with you in case the weather gets worse.

Even if introduces an extreme condition (= whether or not).
E.g. Well, it's true, even if you refuse to believe me.

Even though (= despite the fact that)
E.g. I like her, even though she can be annoying at times.

Given that is used when some fact is already known (= Since/Because).
E.g. Given that this area is liable to flood, it would be unwise in the extreme to consider buying a house here.

Whether...or not
E.g. Whether you agree with Paul McKenna or not, you'll enjoy reading his book.

Assuming that (= in the possible situation that)
E.g. Assuming that the company paid for you, would you take the course?

If + -ing
E.g. If talking helps, you can call a friend.

If + past participle
E.g. If taken too seriously, self-help books can be depressing.

If in doubt (= if you are in doubt/ if you are not sure)
E.g. If in doubt, consult a specialist.

If necessary (if you need to)
E.g. If necessary, you can take a pill to help you calm down.

It would be a pity if
E.g. It would be a pity if you couldn't express your emotions.