Базовая форма – простое настоящее в if-предложении и простое будущее в главной части (при этом форма настоящего времени в if-клозе выражает предположение о будущем).

If it rains, we'll stay at home
I'll give her your love if I see her (не ... 'if I will see her'.)
If the weather clears, we'll go for a walk.
If the weather doesn't clear, we won't go for a walk.
If she finishes early she will go home.
What shall we do if it rains?
If I am better tomorrow, I will get up.
If I have a headache I will take an aspirin.
If I survive this experience, I’ll never leave you again.
Willie will never achieve anything unless he is pushed.

Таким образом выражается предположение, которое кажется говорящему вполне реальным и осуществимым. Такие предложения можно использовать, предлагая кому-то что-либо:

I’ll teach you, if you want.

 
Возможны вариации как в if-предложении, так и в главной части.

A. В if-предложении:

1. be going to

If I'm going to catch the train, I'll have to leave now.
We'll need more chairs if we're going to invite so many people.

2. present progressive:

If he is standing in the rain, he will catch cold.

3. present perfect:

If she has arrived at the station, she will be here soon
If he has finished his work by six o'clock, we will be able to take him with us.
Unless he has done the work to my satisfaction, I will not pay him for it.

В некоторых случаях использование совершенного времени и настоящего примерно совпадают по смыслу:

I'll lend you War and Peace if I've finished it before you go on holiday (= ...if I finish...)
If you haven't paid the bill by Friday, we're taking the carpets back (= If you don't pay...)

Но если подчеркиваются будущие последствия события в прошлом, то следует употреблять совершенное время:

If I've failed my maths exam again, I'm going to give up the course (экзамен я уже сдал, но не знаю результата)
If I fail my maths exam again, I'm going to give up the course (всё еще в будущем)

4. present perfect progressive

If he has been travelling all night, he will need a rest.

5. модальный глагол

В if-предложении можно употреблять can, may и must:

If I can afford it, I will buy it.
Park your car under a tree, if you can find a space.

6. be to (и must – в главной части)

It’s late, and if I am to get any sleep I must go.
If you are to escape, you must leave me and go on alone.

7. imperative

Своего рода условными предложениями можно считать такие, в которых условие выражено инфинитивом. Такие предложения можно сравнить с сложносочиненными:

If you drop that I'll kill you/ Drop that, and I'll kill you.
If you don't drop that I'll kill you/ Drop that, or I'll kill you

Таким образом могут выражаться просьбы, советы, угрозы и т.п.:

comment: Fail to pay and they'll cut oft the electricity
If you fail to pay, they'll cut off the electricity.

request: Tell us what to do and we'll get on with it
If you tell us what to do we'll get on with it.

threat: Stop eating sweets, or you won't get any dinner
If you don't stop eating sweets, you won't get any dinner.

advice: Take a taxi, otherwise you't miss your train
If you don't take a taxi, you'd miss your train.

Таким образом, во всех этих вариантах выдерживается принцип, что в придаточной части должно быть настоящее грамматическое время.

■ should + infinitive

Употребление should выражает меньшую по сравнению с базовой формой вероятность события (например, зависит в свою очередь от еще какого-то события).

If he calls, tell him I'll ring back (обычный тип 1).
If he should call, tell him I'II ring back (if + should)

If anything happens, I will return immediately.
If anything should happen, I will return immediately.
If you should run into Peter, tell him he owes me a letter.
If you should be interested, I will send you a copy of my book/ please let me know.
If that should happen, you will be blamed.
If you (should) see him, please give him my regards
If you (should) happen to see him, please give him my regards
If I should see him, I'll ask him to ring you.
If you should write to her, send her my love.
If you should go to Nairobi, go and see the Snake Park.

Предложения с should звучат несколько более формально и вежливо.

С таким же значением используется happen, причем should и happen могут употребляться вместе:

If you happen to pass a supermarket, perhaps you could get some eggs.
If you should happen to finish early, give me a ring.

При этом чем сложнее сочетание, тем вежливее (вплоть до вычурности) оно звучит:

If you see him, ...
If you should see him, ...
Should you see him, ...
If you happen to see him, ...
If you should happen to see him, ...
Should you happen to see him, ...
Should you by any chance happen to see him, ...

Should можно переносить в начало предложения (опуская союз), что звучит еще более формально:

Should you be interested, I will send you a copy of my book/please let me know.
Should you happen to see him, please give him my regards.
Should you see him, please give him my regards.
Should you be interested in our offer, please contact us.
Should you not wish our agent to call, please let us know.

При отрицании можно использовать только форму should you not или простое настоящее:

If you don't see him (не 'if you shouldn't') ...

■ В if-части условного предложения в виде своего рода исключения может употребляться will.

a) В подчеркнуто вежливой речи, will здесь – модальный глагол со значением «изволить»:

If you help me, we can finish by six.
If you will help me (if you will be so kind as to help me), we can finish by six.

If you will write me a letter about it, I will attend to it at once.
Shall I hold the door open for you? - Yes if you will/would.
If you will/would/could wait a moment I'll fetch the money.
If you will/would agree to pay us compensation we will/would agree not to take the matter any further.
If you will come this way, I'll show you your room.
If your mother will fill in this form, I'll prepare her ticket.

Would еще более подчеркивает вежливость:

If you would write me a letter about it, I will attend to it. . . .
If you would write me a letter about it, I would be most grateful.

If you will/would take your seats, ladies and gentlemen, we can begin the meeting.
If he will/would/could only try harder, I'm sure he'd do well.
I'd be grateful if you will/would let me know soon.
If you will/would follow me, I'll show you the way.
Give me a moment if you would/will.
If you would come this way ...

(В официальной и деловой переписке может с 1-м лицом может употребляться should, чтобы избежать повторения would).

b) Так же с модальным значением, когда will выражает упорное желание или нежелание что-либо делать (на will падает ударение):

A: I'm tired. B: Well, if you will go to bed so late, I'm not surprised.
There's no point in trying to teach the class if they won't pay attention.
If you will eat so much, it's not surprising you feel ill.
If you won't (не "wouldn't) stop smoking, you can only expect to have a bad cough.

c) если возможное событие в if-части зависит от того, что выражено в главном предложении (т.е. в какой мере части предложения «меняются местами» - уже событие, выраженное в if-части будет следствием того, что выражено в главной части):

I can/could lend you five pounds, if that will/would help.

I'll give you $100 if I win the lottery (выигрыш в лотерею - условие).
I'll give you $100 if it'll help you to go on holiday (отпуск – результат, который последует за тем, что я дам деньги).

We'll go home now if you get the car (условие).
We'll go home now if it will make you feel better (результат).

Open a window if it will help you to sleep (можно и ...if it helps you to sleep)
I will be angry if it turns out that you are wrong (нельзя ...if it will turn out...)

d) Иногда (достаточно редко) со значением «не сейчас, но позже», подчеркивая временную отдаленность события:

If it suits you, I'll change the date of our meeting (тип 1).
If it will suit you, (not now, but later) I'll change the date of our meeting.

e) в случаях когда будущее действие уже заранее известно (т.е. фактически нет предположения):

If Ann won't be here on Thursday, we'd better cancel the meeting.
If prices will really come down in a few months, I'm not going to buy one now.

В таких предложениях союз по смыслу близок к since: «так как Энн не будет в четверг… », «так как цены упадут…» и т.п.

(f Will после if употребляется в if/whether-предложениях, которые не являются условными:

I don't know if I'll be ready in time (не ... if I'm ready in time).

 
Теперь посмотрим, что может быть в главном клозе такого предложения.

1. imperative will be -ing, will have -en, will have been –ing

В главной части могут употребляться другие будущие грамматические времена:

If he gets the job he'll be going abroad.
If I don't run the train will have left.
If you don't hurry and get there before five o'clock, he will have left the office and gone home.
If I stay till May, I'll have been working here for 20 years.

2. imperative be going to

If we have fine weather tomorrow, I'm going to paint the windows.
What are you going to do if it rains?

3. imperative imperative

Cancel the match if it rains.
If it rains, cancel the match.
Take another sandwich if you're hungry.
If you have a mobile phone, check that it is turned off.
Come indoors at once if it rains.
Don't come unless I tell you to come.

4. imperative be + to-infinitive

What are we to do if it rains?
If he comes, what are we to do?

5. imperative modals

Если для выражения следствия из условия, выраженного в if-части предложения, глагол кажется слишком «уверенным», то можно употребить модальные с разными оттенками уверенности:

If it's fine tomorrow, we can (= we are free to) go out.
If it's fine tomorrow, we could (= we would be able to) go out.
If it's fine tomorrow, we may (= it's possible) go out.
If it's fine tomorrow, we might (= it's possible) go out.
If it's fine tomorrow, we should (= it's advisable) go out.
If it's fine tomorrow, we ought to (= it's advisable) go out.
If it's fine tomorrow, we must (= it's necessary) go out.

■ В этом случае в if-части предложения также возможны разные варианты:

If she finishes early, she can/could phone me.
If she is arriving today, she may/might phone me.
If she has arrived, she should/ought to phone me.
If she has been waiting, she phone me.
If she can't understand it, she must phone me.

И с модальными глаголами можно употреблять инфинитив в продолженной и совершенной формах:

If I hear from Tim, I may be leaving tonight
If he is in New York he may not have got my letter yet

■Чтобы подчеркнуть зависимость одного события от другого, в главном предложении можно употреблять союз then:

If she can't come to us, then we'll have to go and see her.

 
1. При инверсии (с were, had и should) союз if опускается:

Were she my daughter, ... (= If she were my daughter ... )
Had I realized what you intended, ... (= If I had realised )
Should you change your mind, ... (= If you should change )

■ Отрицательные формы нельзя сокращать:

Had we not missed the plane, we would all have been killed in the crash. (не 'Hadn't we missed ...' )

2. If может иногда опускаться в разговорной речи:

You want to get in, you pay like everybody else. (= If you want ... )
You touch me again, I'll kick your teeth in.

■ Пропуск слов после if

В некоторых типовых случаях глагол be можно опускать – получаются короткие безличные придаточные предложения:

I'll work late tonight if necessary. (= ... if it is necessary/ if it be necessary)
We will sell the car, if necessary (= We will sell the car, if it is necessary).
If in doubt, ask for help. (= If you are in doubt ... )
This unfortunate situation is to be avoided if possible.
If I were innocent, I’d rather be tried here; if guilty, in America.
If in doubt, ask at your local library.
There is little if any good evidence for flying saucers.
I'm not angry. If anything, I feel a little surprised.
He seldom if ever travels abroad.
If about to go on a long journey, try to have a good night's sleep.

 
Базовая форма такой конструкции – простое прошедшее в if-клозе и would + инфинитив в главной части. Форма прошедшего времени выражает здесь не прошлое, а «сослагательность».

If it rained tomorrow we'd stay at home.

1. Этот тип предложений употребляется для возможных событий в настоящем или будущем, которые говорящий считает маловероятными (или даже невозможными).

Разница между, например, if I come и if I came состоит в том, что if I came относится к невозможному, воображаемому или маловероятному событию.

If I become President, I'll… (слова кандидата)
If I became President, I'd… (слова школьника)

If I win this race, I'll… (слова фаворита)
If I won this race, I'd… (слова аутсайдера)

Еще примеры:

If I knew her name, I would tell you (не ‘If I know ...’ )(не ‘If I would know ...’ ) (не ‘... I will tell you’).
She would be perfectly happy if she had a car.
What would you do if you lost your job?
If I was taller, I would become a policeman.
If he had any money, he'd leave home.
If you took a taxi, you'd get there quicker.
If I had the money I should pay you.
If he heard of your marriage he would be surprised.
If you could see me now, you'd laugh your head off.
The older men would find it difficult to get a job if they left the farm.
I should be surprised if it was less than five pounds.
If I frightened them, they might run away and I would never see them again.
Не wouldn't do it unless you ordered him to do it.
Supposing I accepted this offer, what would you say?
If I knew her name, I would tell you.
What would you do if you lost your job?
If you parked your car there (now), they would tow it away.

2. Таким образом можно сделать свое предложение более вежливым:

Will it be all right if I bring a friend? (прямой вопрос)
Would it be all right if I brought a friend? (более вежливый вопрос)

It would be nice if you helped me a bit with the housework.
Would it be all right if I came round about seven tomorrow?

3. Предложения 2-го типа могут быть иногда близки по смыслу к предложениями 1-го типа (т.е. выражать то, что вполне возможно):

If you went by train, you would get there earlier.
If you didn't stay up so late every evening, you wouldn't feel so sleepy in the morning

Эти предложения достаточно близки по смыслу к следующим:

If you go by train, you will get there earlier
If you don't stay up so late every evening, you won't feel so sleepy in the morning.

Но часто с помощью 2-го типа условных предложений выражаются совершенно нереальные предположения:

If I had longer legs, I'd be able to run faster.

4. С первым лицом в британском английском может употребляться should:

If I knew her name, I should tell you.
If I married you, we should both be unhappy.

5. В качестве сокращения употребляется 'd:

We'd get up earlier if there was a good reason to.

 
В if–части предложения могут быть следующие вариации:

1. were (специальная форма сослагательного наклонения глагола be ) вместо was

If I were you, I would keep quiet.
If John were here now (but he isn't), we could play tennis.
Не wouldn't be in difficulties if he were not so foolish.
If I were asked to define my condition, l’d say bored.
If I was/were better qualified, I'd apply for the job
If I were rich, I would spend all my time travelling.
If your mother were here, I'm sure she wouldn't let you eat all those chocolates.

Употребление were считается несколько более «правильным», особенно для чисто воображаемых условий:

If I were the Queen of Sheba, you'd be King Solomon.
If I were a guy, I would look like my dad.
If my nose were a little shorter I'd be quite pretty.

Употребление were желательно в обороте If I were you...:

If I were you, I'd take it back to the shop. It's got a hole in it. (лучше, чем ‘If I was you...’)

Оператор может ставиться в начало предложения (союз при этом опускается):

Were I in your place, I would be very worried

Но такая конструкция значительно более формальна, чем 'if I were in your place' и т.п.

(при этом предложении не может начинаться с Was, Wasn't or Weren't, а только с Were).

■ Were необходимо употреблять в выражениях с 'If I were you/If I were in your position' и 'If it were not for/Were it not for' (так объясняется почему что-либо не произошло)

If I were you/in your position, I'd accept their offer.
If I were Jane/in Jane's position, I'd walk out on him.

If it wasn't for your help, I would still be homeless.
If it weren't for your help, I would still be homeless.
Were it not for your help, I would still be homeless (здесь недопустимо сокращение: Weren't it).
Were it not for the fact that you helped me, I would be homeless (were it not звучит очень формально).

If it wasn't for the fact that Greentown is 20 miles away, I would walk there.
If it weren't for the fact that Greentown is 20 miles away, I would walk there.
Were it not for the fact that Greentown is 20 miles away, I would walk there.

If it wasn't/weren't for Vivian, the conference wouldn't be going ahead.
If it wasn't/weren't for the fact that Jane would be offended, I wouldn't go to the party.

If it wasn't/weren't for his wife's money he'd never be a director (= Without his wife's money ...).
If it wasn't/weren't for the children, we could go skiing next week.
We would not be able to provide after-school sports if it were not for dedicated teachers like Mr Morgan.

2. прошедшее продолженное

It is ranining right now, so I will not go for a walk.
If it were not raining right now, I would go for a walk.

3. If + were to/was to

Такая конструкция выражает предположение о будущем (were можно заменять на was).:

lf you were to touch that wire, you would be killed instantly.
If we were to move north, we would be able to buy a bigger house.
If the boss was/were to come in now, we'd be in real trouble. (= If the boss came ... )
What would we do if I was/were to lose my job?
Even if you were to try, you wouldn't be able to do it.

Оператор можно переносит в начало предложения, но это звучит формально и старомодно (и в такой конструкции уже нельзя заменять were на was):

Were this enterprise to fail, it would be a disaster for us all.
Were the government to cut Value Added Tax, prices would fall.
Were the election to be held today, the Liberals would win easily (или 'If the election was/ were held today...').
Were I not in my 70s and rather unfit, I might consider taking up squash (или If I wasn't/ weren't in my 70s and rather unfit...).

При отрицании нельзя употреблять 'lf he were not to' и возможен только следующий вид:

There'd be a clear case for legal action over this matter were it not likely to make life difficult for all of us (не 'weren't if').

■ В главной части могут употребляться другие модальные глаголы:

If you were to start early tomorrow morning, you would (could, might, ought to, should) be at your destination by evening.

■ Вместо were to в британском английском может употребляться should, но надо учитывать, что для носителей американского диалекта это выглядит достаточно неестественно:

If he should (were to) hear of your marriage, he would be surprised.
If you should be passing my house, you might return the book you borrowed from me.

Конструкция were to обычно не употребляется с такими глаголами как belong, doubt, enjoy, know, like, remember и understand (которые выражают состояние):

If I knew they were honest, I'd gladly lend them the money (не If I were to know...)

If I knew her name ... (не If I were to know her name ... )

4. С помощью этой конструкции можно сделать предложение более вежливым:

Would it be too early for you if we were to meet at 5.30?
- If I asked him, I'm sure he'd help us. - Do you think he would? - Well if I were to ask him nicely.
If I were to (was to) ask, would you help me?
If you were to move your chair a bit, we could all sit down.

5. В главной части возможны не только would и should, но и другие модальные глаголы:

If you were to ask him, he might help you.
If Sue were to make an effort, she could do better.

6. would

В очень разговорной устной речи в американском английском употребляется would в обоих частях условного предложения:

It would be good if we'd get some rain.
How would we feel if this would happen to our family?

7. В главной части условных предложений этого типа могут употребляться модальные глаголы:

If I had another $500, I could buy a car (физически смог бы).
If you asked me nicely, I might get you a drink (возможно бы так поступил).
If you went to London you might see the Queen.
If he took his doctor's advice he might soon be well again.
You could do it if you tried.
If he knew the facts, he could tell us what to do
If you parked your car there (now), they would tow it away/we could keep an eye on it.

Еще примеры:

If he were here he could help us (ability).
If he were here he might help us (possibility).
If he failed, he ought to/should try again (duty).

Возможно употребление продолженного инфинитива после модальных глаголов:

If she were here now she could be helping us.
If he was in New York, he could have met my sister.
If they were in the army they would have been fighting in the jungle most of the time.

 
1. Базовая форма таких предложений – предпрошедшее в if–предложении и would + совершенная форма инфинитива (или другими словами – форма совершенного будущего в прошедшем) – в главной его части.

If it had rained, we would have stayed at home
If you had asked me, I would have told you.
(не 'If you would have asked me…' ) (не 'If you asked me ...' ) (не '…I had told you'.)
If I had been taller I would have joined the police force.
If I had had any sense, I would have kept quiet about it.
If we had gone by car, we would have saved time.

2. Этот тип предложений употребляется, когда речь идет о уже совершившихся в прошлом событиях (а значит, и условие и следствие уже физически невыполнимы).

If I had worked harder at school, I'd have got a better job
If I hadn't been wearing a raincoat, I would have got wet (выражается возможная нежелательная ситуация).
If I had won the pools, life would have been much easier (выражается воображаемая желаемая ситуация в прошлом).
If I had lived in the Stone Age, I would have been a hunter (выражается совершенно невозможная ситуация).
Perhaps if he had realized that, he would have run away while there was still time.
If she had not been ill, she would probably have won that race.
If you had worked harder, you would have passed your exam.
I'd have been in bad trouble if Jane hadn't helped me.
If you had parked your car there (but you didn't), they would have towed it away.
If he had heard of your marriage he would have been surprised.
I should never have got here in time (I should not be here now) if you had not given me a lift in your car.
If you had been at the meeting I should have seen you.

3. В формальном стиле оператор может ставиться в начало предложения:

Had you informed us earlier, we would have taken the necessary steps.
Had the management acted sooner, the strike wouldn't have happened.
Had we not been delayed, the accident would never have happened (в этом случае 'Had . . . not' нельзя сокращать до Hadn't).
Had it not been for the unusually bad weather the rescue party would have been able to save the stranded climber (не Hadn't).

4. 'If I had been you/in your position'

Такие обороты употребляются, чтобы выразить, что мы бы сделали на месте другого человека:

If I had been you/in your position, I'd have accepted their offer (= You should have accepted their offer).
If I had been Jane, I'd have walked out on him years ago.

5. 'If it hadn't been for'

Таким образом объясняется, почему что-либо не произошло в прошлом:

It hadn't been for the rain, we would have had a good harvest.

6. Говоря о прошлом, можно использовать оборот ‘if it had not been for’:

If it hadn't been for Dad, I wouldn't have gone to college (или 'If it wasn't/weren't for...')
If it hadn't been for your help, I don't know what I'd have done.

But for так же может употребляться со значением 'if it were not for' или 'if it had not been for':

But for your help, I don't know what I'd have done.

 
A. Возможные изменения в if–части:

1. Продолженное совершенное время:

If it had been raining this morning we would have stayed at home.
If I had been trying harder, I would have succeeded.

2. could have

If I could have stopped, there wouldn't have been an accident

(Would have и should have в if-части не употребляются)

3. В американском английском в if-части предложения иногда используется простое прошедшее время вместо прошедшего совершенного:

If I knew you were coming I'd have baked a cake.
If I had the money with me I would have bought you one.
If I didn't have my walking boots on I think I would have really hurt my foot.

4. Условие может подразумеваться:

I would have gone with you, but I had to study.
I never would have succeeded without your help.
She ran; otherwise, she would have missed her bus.

5. В разговорной речи в if-части условного предложения 3-го типа могут употребляться would или had + перфектный инфинитив (грамматически это неправильно).

I didn't know. But if I had've known...
We would never have met if he hadn't have crashed into my car.
If I would've had a gun, somebody might have got hurt.
If you wouldn't have phoned her we'd never have found out what was happening.

If I'd have known she was ill I'd have sent her some flowers.
If I'd have known, I'd have told you.
It would have been funny if she'd have recognized him.

B. В главной части возможны следующие варианты:

1. Продолженное совершенное время

If I had not got married, I would still have been living abroad.

2. would с простым инфинитивом.

If my mother hadn't knocked my father off his bicycle thirty years ago, I wouldn't have been here now (= ... I wouldn't be here now.)
If my mother hadn't met father thirty years ago, I would't have been here now (= I would't be here now).
If she hadn't crossed the road without looking, she would have been alive today (= ...she would be alive today).

3. modals

You could have done it if you had tried.
If he had known the facts he could have told us what to do.
If he'd run a bit faster, he could have won.
If I hadn't been so tired, I might have realized what was happening.
If you had parked your car there (but you didn't), we could have kept an eye on it.

If he had been here yesterday he could have told us (ability).
If he had been here yesterday he might have told us (possibility).
If he had received a present he should have thanked her (duty).

Возможны совершенные инфинитивы после модальных глаголов:

If he had been here he could have been helping us in the shop.
If she had been here she could have met my sister.

If you had not told me about it I should (might) never have known (I should still be unaware of) the facts.
If he had taken his doctor's advice he might not have died (he might still be alive).

 
Кроме if в условных предложениях употребляются другие союзы, имеющие похожий смысл.

1. even if употребляется, чтобы выразить, что одна ситуация не повлияла бы на другую:

I would have married her even if she had been penniless.
Even if you don’t get the job this time, there will be many exciting opportunities in the future.
Even if I become a millionaire, I shall always be a socialist.

2. if only употребляется, чтобы сказать о пожелании – близко по смыслу к ‘I wish…’. Придаточное предложение с if only может употребляться и отдельно, без главного предложения

If only I knew more people!
If only I was better-looking!
If only your father were here!

a) would + bare infinitive выражает пожелание о будущем:

If only it would stop raining, we could go out.
If only somebody would smile!

b) past perfect относится к прошлому:

If only she hadn't told the police, everything would have been all right.

С похожим значением употребляется imagine (that):

Imagine we could all fly. Wouldn't that be fun!

3. only if

These activities can flourish only if agriculture and rural industry are flourishing.

Only можно переносить в главное предложение:

I will only come if he wants me. (=I will come only if he wants me.)
He told them that disarmament was only possible if Britain changed her foreign policy.

4. Unless со значением 'if. . . not', 'except if':

Unless it rains, I'll pick you up at 6.00.
Unless the theatre is able to raise $100,000, it will have to close (= If the theatre isn't able to...)
Come tomorrow unless I phone. (= ... if I don't phone / except if I phone.)
I'll take the job unless the pay is too low. (= if the pay isn't too low / except if the pay is too low. )
I'll be back tomorrow unless there's a plane strike.
Let's have dinner out - unless you're too tired.
I'm going to dig the garden this afternoon, unless it rains.
You can't travel on this train unless you have a reservation.
You won’t catch the train if you don't hurry/unless you hurry.
Your parcel will be dispatched this evening, unless you (would) prefer to take it with you now.
Goods will not be dispatched unless they are paid for in advance.
Не wouldn't do it unless you were to order him to do it.

■ If...not, а не unless употребляется если

(a) событие, описываемое в главном предложении, будет неожиданным:

I'll be amazed if Christie doesn't win.

(b) обычно в вопросах:

If you don't pass the test, what will you do?

(c) когда не подходит по смыслу 'only if':

If it wasn't the best performance of Hamlet I've seen, it was certainly the strangest.

(d) unless не употребляется, если смысл высказывания близок к 'because ... not':

OK. So we'll meet this evening at 7.00 – unless my train's late. (= ... except if my train's late.)
My wife will be angry if I'm not home by 7.00. (не 'My wife will be angry unless I get home by 7.00. - She will be angry because I'm not home'.)

I'll drive over and see you, unless the car breaks down. (= ... except if the car breaks down.)
I'll be surprised if the car doesn't break down soon (не 'I'll be surprised unless the car breaks down soon. - I'll be surprised because it doesn't break down'.)

(e) If ...not обычно употребляется в предложениях с нереальным условием, но если главное предложение в отрицательной форме, то можно употребить unless:

If I weren't so tired, I'd give you a hand.
She wouldn't have gone to university unless her parents had insisted.

■ unless, а не if...not употребляется когда

(a) выражается соображение, которое высказывается уже после первого предположения:

We can leave now - unless you'd rather wait for Jack, of course.

(b) после части предложения с условием идет еще и определительное предложение «возвращающее» нас к позитивному предположению в главной части:

We can walk to the cinema unless it's raining, in which case we'll get a taxi.

5. Whether

Whether you lock your car or not, the police will tow it away.
(в таком предложении нельзя заменить на if … or not)

6. On condition (that), provided(that)/providing (that), so long as/as long as

I will let you drive on condition (that)/ = provided (that)/ = providing (that) /= so/as long as you have a valid license.

I'll give you the day off on condition that you work on Saturday morning.
Не says he'll accept the post provided (on condition that) the salary is satisfactory.
Ordering is quick and easy provided you have access to the internet.
Provided that it’s not too much money I’d love to come to Spain.
The oven bakes magnificent bread providing it is hot enough.
Provided the weather keeps like this, the farmers have no need to worry about the crops.
You can borrow my bike providing/provided you bring it back.
It doesn't matter where you put it so long as you make a note of where it is.
They are happy for the world to stay as it is, as long as they are comfortable.
You're welcome to stay with us as/so long as you share the expenses.
So long as you return the book by Saturday, I will lend it to you with pleasure.

On condition (that) обычно употребляется с одушевленными существительными, с другими союзами этой группы это неважно:

We'll be all right so long as it doesn't pour with rain.

7. Suppose/Supposing (that)

С этими союзами можно сделать предположения о будущем и прошлом.

Suppose/Supposing (that) I had/were to have an accident, who would pay? (future)
Suppose/ Supposing (that) I had had an accident who would have paid? (past)

Supposing you'd missed the train. What would you have done?
Supposing my father saw me with you, what might he think?
Supposing the other team wins the match, what will happen to us?
Suppose (supposing) your friends knew how you're behaving here, what would they think?

8. In case

Make a note of my telephone number, in case you want to ring me up.
You'd better take an umbrella with you in case it rains.
I shall take an umbrella in case it rains.

Сокращаем сложное предложение. Безличные обороты/клозы в роли элементов предложения.