1. Could употребляется для выражения способности что-то делать в прошлом, только если из контекста (например, есть другой глагол в форме прошедшего времени) очевидно, что речь идет именно о прошлом:

She [could read] Latin when she was twelve!
Не [could speak] German well when he was young, but he has forgotten most of his German now.
It [could be quite frightening if you were alone in our big old house.
She [could read] when she was four.
My grandmother [could sing] like an angel (можно догадаться, что это было в прошлом).
My last [car could] do 200 kph (слово ‘last’ указывает на прошлое).
In those days everybody [could find] a job (обстоятельство ‘in those days’ указывает на прошлое).

Можно употреблять was/were able to:

She [was able to read] when she was four.

2. Could употребляется в придаточных клозах и косвенной речи:

Can you help me? – What did you say? – I asked [if you could help me].
Can you give me a hand? – What? – I asked [if you could give me a hand].
[You could get a better job] if you spoke a foreign language.
I told you [I could use a typewriter].
I told him [I could help him].

3. Can/could выражает именно возможность что-либо совершить, поэтому, как правило, не употребляется для выражениях законченных в прошлом отдельных действий. В отношении таких действий could выражает сослагательность:

Тоm could pass the examination, we all were sure of that (Том мог сдать и мы были в этом уверены, но предложение не означает, что он его действительно сдал).
Tom could pass the examination (Том мог бы сдать экзамен, но тоже не значит, что он его сдал).

Для выражения законченных действий в прошлом можно употреблять

3.1. Просто Past Simple:

I found a really nice dress in the sale. (не ‘I could find... ’)
Torn passed the examination.
Harry swam across the river.
Аnn didn't catch her train.

(could в таких предложениях не употребляется)

3.2. Manage (предполагает трудности, которые пришлось преодолеть) и succeed:

I managed to run 10 km yesterday. (не ‘I could run 10 km yesterday... ’ )
I managed to buy a really nice coat yesterday. (не ‘I could buy a really nice coat yesterday’.)
After six hours' climbing, we succeeded in getting to the top of the mountain. (не ’… we could get to the top... ’ )
Torn succeeded in passing the examination.
Harry managed to swim across the river.
Anne didn't manage to catch the train.
Did you manage to get to the top of the mountain?
How did you manage to get here in time?
I managed to get /succeeded in getting all my clothes into the suitcase.

3.3. Обороты с get

Не got it done. (‘Не could get it done’ означает, что он мог бы это сделать).

3.4. Оборот be able to:

I was able to pass the examination.
How many eggs were you able to get? (не ‘...could you get?’)

4. Но could можно употреблять, выражая, что что-то не случилось в конкретном случае в прошлом

4.1. С глаголами see, hear, smell, taste, feel, understand, remember:

I [could smell] something burning.
I [could understand] everything she said.
Suddenly she realised she [could smell] something burning.
He spoke so quickly that I [couldn't understand] him at all.
Though I was sitting in the last row, I [could see] the film well.
I [could not] hear him.

4.2. В отношении единичного случая в придаточном клозе:

I'm so glad that you could come.

4.3. При употреблении отрицательной формы couldn't:

I managed to find the street, but I couldn't find her house.
Не said he couldn't come to the meeting.
The box was so heavy that I couldn't lift it.
Не said he was sorry he couldn't lend me the money.
I tried to lift the box but couldn't.

4.4. С наречиями hardly и only (так как они также имеют негативный оттенок).

She could hardly believe her eyes. I could only get six eggs.

5. Употребляется can't, а не couldn't, когда речь идет о том, что невозможно:

There can't be many people in the world who haven't watched television.
The doctor can't see you this morning; he's busy at the hospital.

6. Could+have+past participle указывает на неосуществленную в прошлом возможность:

The President was always available. We could see him at any time (мы могли его видеть)
You never came to see me. Why not? You could have seen me at any time (ты мог, но не делал).

You could have caught the train if you had hurried.
I could have married anybody I wanted to.
I was so angry I could have killed her!
Why did you jump out of the window? You could have hurt yourself.
I could have won the race if I hadn't fallen.
I could have kissed her if I'd wanted to.
Не could easily have done it.

Так можно выразить неудовольствие:

You could have helped me - why did you just sit and watch?
You could have told me you were getting married.

Отрицательное предложение показывает, что возможности что-то сделать не было вообще:

I couldn't have won, so I didn't go in for the race.
I couldn't have enjoyed myself more - it was a perfect day.

Такая конструкция иногда может выражать и предположение:

Who sent those flowers? – I'm not sure. It could have been your mother.

Предложение может относиться к настоящему времени:

He could have been Prime Minister now if he hadn't decided to leave politics.
We could have spent today at the seaside, but we thought it was going to rain, so we decided not to.

■ Иногда употребляется can+have+past participle:

I don't know where she can have gone.

7. Was/were able to предпочтительнее, когда речь идет о единичном достижении в прошлом, а не способности вообще (в этом случае можно употреблять и could и was/were able to):

She swam strongly and was able to cross the river easily, even though it was swollen by the heavy rain (не ‘She swam strongly and could cross...’)
He didn't want to buy a new suit but at last we were able to persuade him.
She wasn't able to pass the exam.

Sue could play the flute quite well/ Sue was able to play... (способность вообще)

Отрицательную форму couldn't можно употреблять в обоих случаях:

He couldn't play tennis.
We couldn't persuade him to buy a new suit.

8. Could звучит естественнее

8.1. В отрицательных предложениях:

I tried to get up but I couldn't move (естественнее, чем ‘...I wasn't able to move’.)

8.2. С глаголами физического восприятия (feel, hear, see, smell, taste) и выражающими умственную деятельность (believe, decide, remember, understand и т.п.):

I could remember the crash, but nothing after that (естественнее, чем ‘I was able to remember...’)

8.3. После the only thing/place/time и all, со значением 'the only thing':

All we could see were his feet. (естественнее, чем ‘All we were able to...’)

8.4. Выражая идею что что-то чуть не случилось, особенно с наречиями almost, hardly, just, nearly:

I [could nearly touch] the ceiling (естественнее, чем ‘I was nearly able to...’)

 
1. Если контекст в предложении не указывает на то, что речь идет о прошлом, could выражает сослагательность:

It can be expensive to keep a cat (это может быть так, и так бывает).
It could be expensive to keep a cat (если бы у нас была кошка, это могло бы быть затратным).

I could never get all these clothes into that suitcase.
Is there anything I can do to help? - No, thank you, there's nothing you could do.

Разницу можно видеть и на примерах с сложноподчиненными предложениями (в прошлом и будущем):

As he was not interrupted, he finished (was able to finish, managed to finish, succeeded in finishing) the work by evening.
If people did not interrupt him, he could (would be able to) finish the work by evening.

If he is not interrupted, he can (will be able to) finish the work by evening.
If he had not been interrupted, he could have finished (would have been able to finish) the work by evening.

Как и в русском языке, сослагательность придает высказываниям более вежливый оттенок и/или неуверенность:

Could you please give me a stamp?
Where shall we go tomorrow? We could go to the restaraunt.
Come when you like. I could see you at any time.
You could go now if you like(d).
Could I borrow your pen?
Could you lend me five pounds until tomorrow?
Do you think you could help me for a few minutes?
When you've finished the washing-up you can clean the kitchen. Then you could iron the clothes, if you like.
If you haven't got anything to do you could sort out your photos.
Excuse me. Could you tell where the theatre is?
Do you think I could use your pen?
I wonder if they could help us.
Could I have the sugar, please? (за столом)
I could mend your bicycle for you, if that would help.

2. Could может выражать неудовольствие:

You could ask before you borrow my car (ты мог бы меня спросить…).

 
1. В отношении будущего, can употребляется, когда возможность в будущем прямо связана со способностями, решениями или ситуацией в настоящем:

She [canwin] the race tomorrow if she really tries.
I've bought the tent, so we [can go] camping next weekend if we want to.
I haven't got time today, but I [can see] you tomorrow.
Can you come to a party on Saturday?

В остальных случаях предпочтительнее will be able to:

I'll be able to speak French at the end of this course. (не ‘I can speak French...’)
I'll be able to use a typewriter perfectly after a few more lessons.
One day people will be able to go to the moon on holiday. (или ‘…it will be possible to go...’ )

Причем когда речь идет о возможности, полученной благодаря обстоятельствам (а не личным способностям), обычно можно употреблять и can и более явно выразить будущее время:

We can sit at home tomorrow and watch the match in comfort.
We’ll be able to sit at home tomorrow and watch the match in comfort.

2. Could может относиться к будущему (здесь «смесь» возможности и вероятности):

There could be another rise in prices next month.

■ Сan может выражать разрешение что-либо делать (=I am allowed to), т.е. употребляться вместо may:

Permission has been granted. We can go now.
You can drive for a year in Britain with an international license.
If you're under 18, you can't drive a car in Russia.

С помощью вопроса ‘Can I . . . ? ’ можно спросить о разрешении:

Can I borrow your pen for a moment? Ответом может быть ‘Yes, you can’ или ‘No, (I'm afraid) you can't’.

3. Could /be allowed to можно употреблять для выражения разрешения в прошлом, если имеется ввиду разрешение вообще. Говоря о «единичном» разрешении употребляется was/were allowed to, но не could:

Anyone was allowed to fish in the lake when the council owned it. (или ‘...could fish...’)
Although he didn't have a ticket, Ken was [allowed to come in]. (не ‘...could come in’.)
When I was a child, I [could watch] TV whenever I wanted to.
Yesterday evening, Peter [was allowed to watch] TV for an hour. (не ‘...Peter could watch TV for an hour’.)

В отрицательных таких предложениях можно употреблять и wasn't/weren't allowed to и couldn't в обоих случаях:

We couldn't open/weren't allowed to open the presents until Christmas morning.
Peter couldn't watch TV yesterday because he was naughty.

4. Could употребляется в условных предложениях, выражая сослагательность:

He could borrow my car if he asked (я бы ему разрешил).

Сослагательность, выражаемая с помощью could, делает вопрос более вежливым (но в ответах обычно употребляется только can):

Could I ask you something? – Yes, of course you can. (не ‘... of course you could’)

В вопросах с целью получить разрешение может также употребляться may/might, но это звучит более формально.

5. Can и could обычно употребляются вместо may, когда речь идет о правилах и законах:

Can everybody park here? (не ‘May everybody park here?’)

6. Could также употребляется в косвенной речи:

She said I could come as often as I liked.

7. Can в этом значении может относится к будущему:

Permission is granted. We can go next week (или ‘we’ll be allowed to go…’).

■ C помощь can можно выразить обычные или типичные события:

Scotland can be very warm in September.
Ann can really get on your nerves sometimes.

■ Can/could always означает: «можно, если нет ничего лучше»:

I don't know what to get Mark for his birthday. – Well, you can always give him a book token.
What are we going to eat? – We could always warm up that soup.

■ Часто употребляется оборот can't help:

She's a selfish woman, but somehow you can't help liking her.
Excuse me – I couldn't help overhearing what you said.
Sorry I broke the cup – I couldn't help it.

В американском английском с тем же смыслом употребляется ‘can’t help but + infinitive’:

I can't help but wonder what I should do next.

 
Could (но не can) может употребляться для предположений о будущем:

It could rain this afternoon. (не ‘it can rain this afternoon’)
It could rain later this evening, perhaps. (не ‘it can rain later…’)
I could possibly have a new job soon. (не ‘I can possibly have…’ )

Но can't можно употреблять, выражая негативную уверенность:

It can't be true. (= It is not possible that it is true.)

 
May употребляется для выражения разрешения/отказа в разрешении что-либо сделать и в вопросах с целью разрешение получить (в формальной речи):

May I take a swim? Yes, you may.
You may enter.
He may go to the park tomorrow if he behaves himself.
May I put the TV on? – Yes, of course you may.
May I borrow the car? – No, I'm afraid you may not.
Students may not use the staff car park.
Borrowers may not (are not permitted to) take out of the library more than two books at a time.

Так как глагол may звучит достаточно формально, то в разговорном языке вместо него обычно употребляется can:

Can I go for a swim this afternoon, mother?
Can I go out and play? No, you can't.

Can I look at your paper? (разговорно)
Excuse me, may I look at your newspaper for a moment?(очень формально)

ПРОШЛОЕ

Might как правило, не употребляется для выражения разрешения в прошлом и это передается другими способами:

You could/were allowed to take every Friday off last year.

Но might может употребляться в косвенной речи в качестве «заменителя» may:

The Manager says that we may leave our coats in the downstairs toilet.
She told him yesterday he might not go on the trip.
What are you doing here? – Peter said that I might look round (звучит очень формально).

 
1. Might выражает «сослагательность» (как русское «бы»):

Might I speak to you for a moment?
Might I borrow your pen?

Такие вопросы звучат очень формально и несколько естественнее употреблять косвенные вопросы:

I wonder if I might have a little more cheese (более естественно, чем ‘Might I have ...?’)

Ответ ‘Yes, you might’ также звучит достаточно неопределенно, но зато ‘No, you might not’ выражает вполне твердый отказ.

2. С помощью might+have+past participle выражается, что что-то могло произойти, но не произошло:

You were stupid to try climbing up there. You might have killed yourself.
If she hadn't been so bad-tempered, I might have married her.
You oughtn't to have driven that car with the brakes out of order. You might have had a serious accident.
Не might have come if we had asked him (но мы не просили).

(иногда употребляется May+have+past participle, но это считается не очень правильным: ‘You were stupid to try climbing up there. You may have killed yourself’.)

Так можно выразить неудовольствие:

You might have asked me to your wedding! (звучит формально)
She might have told me she was going to stay out all night (также довольно формально).
She's gone without us. She might/could have waited!
You might/could have done the ironing instead of leaving it all to me.

(на might/could часто падает ударение).

3. Часто между may+have+past participle и might +have+past participle есть существенная разница:

Не may have been hurt (это возможно, но неизвестно).
Не might have been hurt (но не был).

Но обе формы могут быть использованы для предположения (это обычно ясно из контекста):

Do you think Jean may/might/could have completed the report by now?
Don't play with knives. You might get hurt.
(см. употребление may/might для предположений)

 
1. May может явно относится к будущему времени:

You may take next Friday afternoon off.

■ May и might, как правило, не употребляются, когда речь идет об уже полученных разрешениях/отказах, правах что-то делать, когда их уже имеют и правилах/законах. В этом случае употребляются can/could и be allowed:

These days, children can/ are allowed to do what they like (не ‘...children may do what they like’.)
I could / was allowed to read what I liked when I was a child. (не ‘I might read what I liked... ’)
Can you / Are you allowed to park on both sides of the road here? (более естественно, чем ‘May you park...’ ?)

2. May может употребляться для выражения возможности в значении очень близком к can/be possible (в достаточно формальном языке):

You may go (you can go/ it is possible to go) from A to В by changing trams at C, or you may (can) go by way of D, but you cannot go (it is impossible to go) there direct.
Specimen copies of these textbooks may be obtained on application to the publisher.
A plan of the new housing estate may be seen at the offices of the Town Council.
The weather has been excellent and we may expect a good harvest.
Не said he thought we might expect a good harvest.
With such a strong Ministry we may hope for an improvement in the country's affairs.

(в отрицательных таких предложениях можно использовать cannot, но не may not).

3. В похожем значении may может употребляться в научном или формальном языке для выражения возможности с некоторой «примесью» вероятности (о типичных вещах):

The seeds from the plant may grow up to 20 centimetres in length.
A female crocodile may lay 30-40 eggs.
The flowers may have five or six petals, pink or red in colour.
Children of divorced parents may have difficulty with relationships.

В таких предложениях можно употреблять can, что будет звучать менее формально.

4. С помощью might можно выразить типичные случаи и в прошлом (звучит литературно):

In those days, a man might be hanged for stealing a sheep.
During the war, the police might/could arrest you for criticising the king.
Years ago children might/could be sent down mines at the age of six. (passive form)

5. May может употребляться в вопросительных предложениях такого рода (звучит формально):

And how much did you pay for your new car, if I may ask?
How far might that be from here? и далеко ли это отсюда?

Такие вопросы могут звучать иронично-высокомерно:

And what may you want?
And how old may/might you be?
And who may/might you bе?

6. Might употребляется в предложениях такого рода:

You might see if John's free this evening (мог бы узнать…).
You might try asking your uncle for a job (мог бы попросить..).

7. Might может употребляться для выражения недовольства:

You might ask before you borrow my car (мог бы и спросить).
You might try writing (могли бы и написать).
She might have told me she was going to stay out all night.
You might at least have offered to help.

8. May (но не might) употребляется для выражения пожеланий (звучит весьма формально):

I hope that the young couple may enjoy many years of happiness together.
Let us pray that peace may soon return to our troubled land.

May you both be very happy! May God be with you.
May the New Year bring you all your heart desires.
May God bless you!
May you have a long and happy life!
Long may you live to enjoy it!

В разговорном языке употребляют обычно повелительное наклонение:

May you have a good time! → Have a good time!
May you enjoy yourselves! → Enjoy yourself!

 
1. Как и все модальные глаголы (кроме shall) may/ might может употребляться для выражения предположения с большой степенью неуверенности (might выражает, вероятно, наибольшую степень неуверенности из всех модальных глаголов):

I may go to London tomorrow (может быть поеду, а, может быть, и нет)
Joe might come with me (даже значительно вероятнее, что не поедет)

It may rain tomorrow.
I may be away from home tomorrow.
Не may need to borrow money.
That may, or may not, be true.
It's so quiet (that) one may hear a pin drop.
If I ask him again, he may refuse.

Иногда (в том числе добавляя well), можно выразить и достаточно сильную уверенность:

I think it's going to rain. – You may well be right - the sky's really black.
He may well be a spy.

 
1. В придаточных предложениях might «работает», как форма прошедшего времени глагола may:

It was so quiet (that) one might hear a pin drop.
I was afraid that if I asked him again, he might refuse.
I may go to Scotland .. - What? - I said I might go to Scotland.
Не said he thought it might rain.

В остальных случаях в отношении прошлого might обычно не употребляется:

I felt very hot and tired. Perhaps I was ill. (не ‘... I might be ill’.)

Но might (как в примере в начале), как и may, может выражать предположения в отношении настоящего и будущего:

Take an umbrella. It will rain before evening.
You'd better take an umbrella. It may rain before evening.
I think you should take an umbrella. It might rain before evening.

He's going to the USA in May (согласно его планам).
He may/might go to the USA in May (возможно)

I think Labour are going to win. – You may be right.
Peter might phone. If he does, ask him to ring later.
Where's Emma? - I don't know. She might be out shopping, I suppose.
I'm not quite sure where to go for my holidays but I may go to the USA.
The weather forecast is not very good. It might snow this evening.
I might paint the kitchen purple.
If you went to bed for an hour, you might feel better (условное предложение).

2. Инфинитив после may/might может быть и в продолженной форме:

He may/ might be going to the USA in May .
Malcolm isn't in his office. He may/might be working at home today.
Don't come at 6. I may/ might be watching my favourite film on television.

3. Форма might добавляет «сослагательности» и обычно выражает меньшую уверенность, чем may.

May have + past participle употребляется для предположений в отношении прошлого и будущего. Might have + past participle также может употребляться в этом же смысле, а не только для выражения того, что могло произойти, но не произошло (He might have been killed!).

3.1. Прошлое

Polly's very late. She may have missed her train. (= It is possible that she missed ... )
Не isn't back yet. He may have had an accident.
I can't find my key anywhere. - You may have lost it while you walked with your dog.
I wonder why Ann didn't answer the doorbell. - Well, I suppose she may have been in the bath.
What was that noise? - It might have been a cat.
I can't find my bag anywhere. - You might have left it in the shop.
Why didn't she answer the phone? - She might have gone shopping.
Why didn't he say hello when he passed us in the street? - He might have been day-dreaming.

3.2. Будущее:

His maths may/might have improved by the time the exam comes round.
When i go to vienna I may/might be staying with richard, but i'm not sure yet.
By the end of this year I might have saved some money.

 
ОТРИЦАНИЕ

Необходимо помнить о разнице в употреблении may/might not (= ‘perhaps ... not ...’) и can/could not (часто означает ‘it is certain that ... not...’)

You might win. (= Perhaps you will win.)
You might not win. (= Perhaps you won't win.)
You can't win. (= You certainly won't win.)

She may be at home. (= Perhaps she is at home.)
She may not be at home. (= Perhaps she is not at home.)
She can't be at home. (= She is certainly not at home.)

It may/might not rain tomorrow. (= Perhaps it will not rain.)
It can't/couldn't possibly rain tomorrow. (= It will certainly not rain.)

It may not be true. (= Perhaps it is not true.)
It can't be true. (= It is certainly not true.)

He may/might not have understood. (= Perhaps he did not understand.)
He can't/couldn't have understood. (= He certainly did not understand.)

ВОПРОСЫ

В значении, выражающем предположение may не употребляется в прямых вопросах:

Do you think you'll go to the Alps? (не ‘May you go...?’)

Are you likely to go camping this summer? (не ‘may you go camping...?’)
Are you likely to be in Spain again this summer? (не ‘May you be in Spain...?’)
Has Emma gone shopping, I wonder? (не ‘May Emma have gone shopping? ’)
Could it be that you don't want to leave? (не ‘may it be that you...?’)

Но may может употребляться в косвенных вопросах (когда вопрос выражается придаточным предложением – например, после ‘Do you think...’).

Do you think you may go camping this summer?

Might может употребляться и в прямых вопросах, но это звучит формально:

Might you go camping? (более естественно: ‘Do you think you may/might...?’)
Might they be persuaded to change their minds?

■ May и might могут выражать и возможность и вероятность:

You may/might walk miles and miles through the forest without meeting anyone.

■ May/might может употребляться, выражая цель или результат в придаточных предложениях с глаголами ‘hope’, ‘trust’, ‘fear’ и т.п. после ‘that’ и ‘so that’ (как правило, есть оттенок случайности). Такие конструкции звучат достаточно литературно и в разговорной речи вместо них употребляются обороты с will/would:

I trust that this arrangement may (will) meet with your approval.
Не trusted that the arrangement might (would) meet with our approval.
I hope he may succeed (succeeds/ will succeed).
I hoped he might succeed (would succeed).

■ Употребляется оборот may/might ... but:

He may be clever, but he hasn't got much common sense.
It may be a comfortable car, but it uses a lot of petrol.
She might have had a lovely voice when she was younger, but...
The painting may not be a masterpiece, but you've got to admit that the colours are striking.
She might not have danced very gracefully, but she had a lot of energy and enthusiasm.

В этом обороте may/might может относится к тому, что является фактом, а не предположением:

You may be my boss, but that doesn't mean you're better than me.

■ Оборот may/might as well выражает идею, что можно что-то сделать просто за неимением лучшего:

- Where shall we go tonight?
- I don't know. Any ideas?
- Well, there's a party at Brigs. A lot of people will be there.
- We [might as well go] there then. There's nothing else to do.

We [may as well go] to the party. We've nothing else to do.
Shall we go shopping now? - We [might as well].
There's nobody interesting to talk to. We [may as well go] home.
I'll have to wait half an hour for the next train, so I [might as well walk].

(в таком обороте разницы между may и might почти нет).

Might as well употребляется также, чтобы сравнить две одинаково непривлекательные возможности:

This holiday isn't much fun. We [might just as well be] back home (ничего не потеряем).
You never listen – I [might as well talk] to a brick wall.