In all their beauty...
can express different things: ability, willingness permission, intention possibility, certainty obligation / necessity advice, suggestions requests, offers & invitations... meaning depends on the context
She can play three instruments. He can speak five languages, while I can’t speak any. She can go to music room to practice. we use can to say that something is possible: that someone has an ability or an opportunity negative is cannot or can’t in formal contexts we use be able to I will be able to come if I finish on time. He is good with computers, he is able to write programs.
for ability and opportunity in the past we use could or was/were able to She could play the piano when she was four. OR She was able to play the piano when she was four. if the ability or opportunity resulted in a particular action, we use was/were able to, not could The car was able to stop before the crash. He was able to come because he finished on time.
asking permission (can, could, may): Can I use your pen? Could we borrow your ladder, please? (more polite) May I see the letter? (rather formal) giving permission (can, may): You can wait there if you like. Could I borrow your pen? – Of course you can. You may telephone from here. (a written notice)
refusing permission (can’t, may not): Can we stay here? – I’m afraid you can’t. Bicycles may not be left here. (a written notice) talking about permission/rules (can, could, be allowed to): Each passenger can take one bag onto the plane. In the 1920s you could drive without taking a test. It isn’t allowed to smoke in here.
we use must & have to to say that something is necessary i.e. there is an obligation to do it You are leaving school soon– you must think about your future. I have a lot to do so I have to work at weekend, too. must is used only in the present, in all other structures we use have to I had to take fifty exams to get a degree. He will have to finish work next week.
we use must when the speaker feels that something is necessary; the obligation involves the speaker’s opinion – it’s personal You must exercise. (I’m telling you.) We must be quiet. (He’s telling us.) we use have to when the situation makes something necessary; it is a general obligation based on a law or rule or on someone’s authority – it’s impersonal I have to exercise. (The doctor told me.) We have to be quiet. (That’s the rule.)
have to has all forms, must does not He must go. – He has to go. negatives do not have the same meaning mustn’t means that something is forbidden; don’t have to expresses absence of obligation You don’t have to buy anything, you can just look. You mustn’t steal other people’s things – it’s wrong. have got to means the same as have to have got to is informal & used mainly in the present I’ve got to make some sandwiches for dinner.
should & ought to express mild obligation, suggestions or advice – they express what is, in the speaker’s opinion, the best thing to do we often use them with I think or I don’t think... You are always asking for money. I think you should spend less. And you ought to be more careful with money. I don’t think you should take the driving test here. You shouldn’t smoke that much. You’ll get ill!
we use mustn’t to say that something is a bad idea or even forbidden You mustn’t drop these glasses. They’ll break. You mustn’t wear your best clothes for gardening! we use needn’t when something is not necessary You needn’t wash those glasses. They’re clean. You needn’t wear your best clothes. Put on whatever you want!
there is a difference in meaning between didn’t need to and needn’t have we use didn’t need to when something wasn’t necessary and, therefore in most cases, wasn’t done Mark didn’t need to hurry. There was plenty of time. I didn’t need to go to the shops because there was enough food. we use needn’t have when something was done but it wasn’t necessary and it was a waste of time Mark needn’t have hurried, he arrived half an hour early. I needn’t have gone to the shops, dad already went.
for polite requests we use can, could, will & would there are two ways of asking things: Can you help me? Could you give me a hand? Will you pass the salt, please? Would you mind waiting here? OR Can I talk to you? Could I have a word with you? can is more familiar, while could is more formal Could I & Could you can be used in all kinds of situations
to express suggestions we use shall/should Shall we go for a walk? Should I open the window? It’s a bit stuffy. to express offers we use will & can I will carry that bag. Just leave it here. I can give you a lift to the station. to offer food or drink we use would like Would you like a piece of pie? Would anyone like more coffee?
we use will & won’t to express what we believe is true about the present or to predict a future action the truth or certainty is taken more or less for granted I’ll see you later. His new book will be out next month. we use must & can’t for what we see to be the most logical or rational interpretation of the situation can’t in this use is the negative of must less certain than will I had my keys a minute ago, they must be here. Nick can’t be in London, I saw him this morning.
should expresses what may reasonably be expected to happen it means if everything has gone according to plan it has the idea of what we want to happen & it isn’t used to express negative or unpleasant ideas Our guests should be here soon. (if they haven’t got lost) We should be moving into the new house next month. You should pass the exam, you worked really hard.
we use may to say that something is possible or quite likely might is more tentative & less certain than may we can use them for the present or the future It may/might be the postman. (=Perhaps it’s him.) I may/might go out tomorrow. (=Perhaps I’ll go.) we use could to say that something possible but not very likely; the meaning is similar to might The story could be true, I suppose. You could win the lottery!
may not & might not express that something negative is possible He may not get the job. She might not be in. couldn’t expresses something impossible He is afraid of heights and couldn’t climb the roof. I’m completely unfit and couldn’t run a marathon.
we express past probability with modal verb + perfect infinitive (= modal + have + past participle) the degrees of certainty are the same as in the present/future will have done is the most certain, and may/might/could have done the least certain would have thought is common to express an assumption or supposition It must have been a great party. Everyone stayed until dawn. Where is he? He should have been here ages ago! You’d have thought she’d remember her first boyfriend.
should have done & ought to have done express advice or criticism about a past event; the sentence expresses what is contrary to facts You should have listened to my advice. She shouldn’t have told you that. I ought to have drawn you a map. You wouldn’t got lost then. should have done can be used for comic effect – the suggestion is because it was so funny / interesting You should have seen his face when she told him. You should have been here yesterday.
could have done expresses an unrealized past ability; somenone was able to do something but he/she didn’t We could have won the match but we didn’t try hard. it also expresses a past possibility that didn’t happen Don’t you ever drive like that! We could have got killed. it is used to criticize people for not doing things You could have told you’ve got the tickets for the show. He could at least have done the dishes after lunch.
might have done expresses something similar to should have done You might have helped, you know. You might have as well passed those exams. it also expresses a typical action of someone or something She might have known he would cheat on her. I might have known he wouldn’t be there on time.
by Irene, 2009