Level: beginner
Possibility and impossibility
We use could to show that something is possible, but not certain:
They could come by car. (= Maybe they will come by car.)
They could be at home. (= Maybe they are at home.)
We use can to make general statements about what is possible:
It can be very cold here in winter. (= It is sometimes very cold here in winter.)
You can easily get lost in this town. (= People often get lost in this town.)
We use can't or cannot to say that something is impossible:
That can't be true.
You cannot be serious.
Level: intermediate
We use could have to make guesses about the past:
It's ten o'clock. They could have arrived by now.
Where are they? They could have got lost.
We use could to make general statements about the past:
It could be very cold there in winter. (= It was sometimes very cold there in winter.)
You could easily get lost in that town. (= People often got lost in that town.)
We use can't have or couldn't have to say that a past event was impossible:
They know the way here. They can't have got lost!
If Jones was at work until six, he couldn't have done the murder.
Ability
Level: beginner
We use can and can't to talk about someone's skill or general abilities:
She can speak several languages.
He can swim like a fish.
They can't dance very well.
We use can and can't to talk about the ability to do something at a specific time in the present or future:
I can see you.
Help! I can't breathe.
We use could and couldn't to talk about the past:
She could speak several languages.
They couldn't dance very well.
Level: intermediate
We use could have to say that someone had the ability or opportunity to do something, but did not do it:
She could have learned Swahili, but she didn't want to.
I could have danced all night. [but I didn't]
Permission
Level: beginner
We use can to ask for permission to do something:
Can I ask a question, please?
Can we go home now?
could is more formal and polite than can:
Could I ask a question please?
Could we go home now?
We use can to give permission:
You can go home now.
You can borrow my pen if you like.
We use can to say that someone has permission to do something:
We can go out whenever we want.
Students can travel for free.
We use can't to refuse permission or say that someone does not have permission:
You can't go home yet.
Students can't travel for free.
Requests
We use could you … as a polite way of telling or asking someone to do something:
Could you take a message, please?
Could I have my bill, please?
can is less polite:
Can you take a message, please?
Offers
We use can I … to make offers:
Can I help you?
Can I do that for you?
We sometimes say I can ... or I could ... to make an offer:
I can do that for you if you like.
I could give you a lift to the station.
Suggestions
We use could to make suggestions:
We could meet at the weekend.
You could eat out tonight.
Questions and negatives
We make questions by putting the subject after can/could:
| Can I ...? Could I ...? etc. |
Can you ...? Could you ...? |
The negative form is can't in spoken English and cannot in written English.
We sometimes say cannot, but it is very emphatic.
The negative form of could is couldn't in spoken English and could not in written English.
- can and could: possibility 1
- can and could: possibility 2
- can and could: other uses 1
- can and could: other uses 2
Hello Yigido,
All of the modal verbs have several different meanings and uses. In this case, it sounds to me as if 'couldn't' is speaking about a hypothetical situation: if he wanted to be a basketball player, he could not be one because he isn't tall enough.
Does that make sense?
All the best,
Kirk
The LearnEnglish Team
Hello Yigido,
I think I'd recommend you ask your teacher about this one, as he or she will know what exactly the mean to say. In general, though, 'could' refers to ability in the past, or, as I mentioned, it can refer to a hypothetical situation (with the meaning of 'would be able to').
Hope this helps.
All the best,
Kirk
The LearnEnglish Team
Hello Mison,
It's fine to use 'could' in that way. Well done!
Peter
The LearnEnglish Team
Hello aliakar86,
I'm afraid that it's not correct to use 'mustn't have' in the ways you ask about because in English you can't prohibit something that already happened. For example, it's not correct to say to your friend 'You must not have gone outside' -- instead, you should say 'You shouldn't have gone outside'.
Similarly, to your friend who got poor exam results, you should say 'You should have studied more' instead of 'You must have studied more'.
It is correct to use 'must have' for deductions. You can see more about this on our Modals – deductions about the past page. I think that should be quite clear, but if you have any more questions, please let us know.
All the best,
Kirk
The LearnEnglish Team
Hello IsabelTim_123,
'may be', 'might be' and 'could be' would all mean the same thing in this sentence: these animals are possibly dangerous, but I'm not sure. You might say this, for example, when you see some animals you're unfamiliar with (e.g. wild pigs) and you really don't know anything about them. But since they are wild animals, there is the possibility that they are dangerous.
'can be' is used to speak more about a possibility we are familiar with -- it suggests that you know something about the animals. If, for example, you see those wild pigs and know for a fact that in some situations they are dangerous --perhaps your grandfather told you this -- and using 'can' would express this idea. Perhaps they won't be dangerous in this situation, but you know that in some cases they are.
Hope this helps you make sense of it.
All the best,
Kirk
The LearnEnglish Team
Hi smit,
Yes, that's right! To work out which meaning is intended by a speaker or writer, we need to consider the context. That includes other things the speaker or writer says, and details about the situation (e.g. the place, the time, the relationship between the speakers, other topics in the conversation).
The examples above are isolated sentences, so they don't have much contextual information. For example, one sentence above is:
But, in real speaking or writing, it would have more context, for example:
The context gives us clues (e.g. when she was little) to show that could means 'past ability' here, and not 'possibility'.
Does that make sense?
Best wishes,
Jonathan
The LearnEnglish Team
Hi smit,
In this example, could doesn't work. Could is for a past ability (not present ability). Could can mean possibility in the present, but speaking English is an ability, not a possibility.
If I'm not 100% sure, I would say: She might be able to. (Might shows a lack of certainty.)
Best wishes,
Jonathan
The LearnEnglish Team
Hello IsabelTim_123,
In 1 and 2, 'could' is also possible and I'd understand it to mean the same thing. In 3, there is nothing grammatically wrong with saying 'can', but it's not really an appropriate response to the question. The question asks for ideas and usually we use a hypothetical form like 'could' to answer such a question, not a form that speaks about ability. In 4, 'cannot have' is not correct because the sentence is speaking about an unreal past, i.e. a past condition that didn't really exist. 'cannot have' makes a statement about a real past action which we think did not occur.
All the best,
Kirk
The LearnEnglish Team
Hello Anisha00329,
Yes, you could use 'can' is all three of those sentences to mean the same thing.
As for the sentences about a rash, both 'can' or 'may' are also possible here if you're speaking about a general possibility, but 'could' is also fine if, for example, you're a concerned parent looking at the rash and deciding whether to take that person to the hospital.
All the best,
Kirk
The LearnEnglish Team
Hello dkbc,
Those forms are possible for all full modals; verbs like need and dare are not always treated as modal verbs, and in fact are slowly transitioning to being normal verbs rather than modal verbs. Verbs like have to and ought to are, at best, semi-modals, and used to is generally described as a marginal modal.
For some modals it's hard to imagine a context in which they would be used because of the particular meaning of the verb. For example, while can have done is a possible form, it is very hard to imagine a context in which it would be used naturally.
Peter
The LearnEnglish Team
Hi Lucas_xpp,
In your first sentence, could is used to show possibility. You could replace it with may or might but not with can, which would show ability, not possibility.
In your second example, could is used to show past ability. You could use can here, but it would change the meaning to present ability. Given that the situation is still unresolved, can works fine here.
In your third example, you could use would. Both could and would can be used in this type of polite request.
Peter
The LearnEnglish Team
Hi Anisha00329,
In the first sentence, could not shows inability in the past. You might argue that the situation (cutting jobs) is a present situation, not a past one. But by using the past form could not, the speaker frames it as a past action. It may be referring to the time that the job cuts were decided (which is a time before the current announcement, i.e. a past time).
In the second sentence, could is used to show hypothetical possibilities, not real ones. It's not claiming that this thing actually is or can be interpreted or understood in all these ways in reality.
Best wishes,
Jonathan
The LearnEnglish Team
Hi AsahiYo20,
I'll try to answer your questions in turn.
Does that make sense?
Best wishes,
Jonathan
The LearnEnglish Team
Hello Sharath.v,
It's hard to be absulutely certain without knowing the context, but I think could is necessary here because the whole sentence is in the past, as shown by the past tense verb gave.
Peter
The LearnEnglish Team
Hello Najmiii3579,
Your first sentence looks rather odd to me. I think the normal form would be either [can't be > isn't wearing] for present meaning or [couldn't be > wasn't wearing] for past.
With your second sentence, it's difficult to say for sure without knowing the context and intention of the speaker. A word might be possible in theory, but change the meaning in such a way that it is highly unlikely, and we would have to describe each context in detail to explain.
If you can tell us what you want to say (i.e. what meaning you want to convey) then we'll be happy to help you to do so.
Peter
The LearnEnglish Team
Hello cms10,
In the first sentence, both may and can are possibly alternatives to could in terms of grammar, but they change the meaning. May would tell us that the persion is allowed to play - not prohibited. Can woud be more similar to could but would make the situation more real. If we use could then the situation is hypothetical. If we use can then it suggests that he has a real possibility of playing for any team - he has offers and can choose amongst them, for example. For this reason, could is preferable in this context.
The meanings would be the same in the second sentence: may would describe what is allowed (by the rules, for example); can would describe what is possible and likely or realistic; could would describe what is hypothetically or theoretically possible.
Peter
The LearnEnglish Team
Hello cms10,
As I see it, in this sentence, 'can' is used to speak about ability -- if I replace 'can' with 'are able to', the sentence still works. The phrase 'the earliest' somehow makes it clear that the sentence is not about a possibility, but rather is more like a prediction or even promise.
To convey the idea of a possibility you're not certain about, you could use 'may', 'might' or 'could': 'We might/could/may finish it next Friday'. Notice that it doesn't work to use the phrase 'the earliest' here.
Hope this helps.
All the best,
Kirk
The LearnEnglish Team
Hello PabloTT,
Yes, you could use 'could not hear'.
To be honest, I think the best phrase here would be 'would not hear' because it expresses the intention of the person (presumably the judge) making the decision.
Peter
The LearnEnglish Team
Hi MarciaBT,
Yes! When could you start? also works fine.
The versions with may or might are possible, but less common.
Does that make sense?
Best wishes,
Jonathan
The LearnEnglish Team
Hi MarciaBT,
No problem. Yes, could shows more politeness. Since a job interview is often the first time that the people have met, that's definitely the option I would choose.
Best wishes,
Jonathan
The LearnEnglish Team
Hi AsahiYo20,
Can works fine in each sentence. However, the use is different in each example. The first sentence uses can to express possibility. The second uses can to express ability. This affects whether or not could can be used.
Even though if is not used, the first sentence is a form of conditional, expressing a condition and a dependent result. Could would make the sentences hypothetical and would require changes in the first clause:
In the second sentence, could would have a past meaning (past ability), and so the verb in the first clause would also need to be past:
Peter
The LearnEnglish Team
Hello again AsahiYo20,
The first sentence does not express future possibility but rather describes the present situation. It could be an answer to a question such as 'Why isn't the restoration work being done?', for example.
The second sentence is also not about the future. It describes a person's job in general terms, not a particular future event. It would be an answer to a question such as 'What does your job entail?' and not 'What are you doing next week?'
Peter
The LearnEnglish Team
Hi brian1010,
I can't be absolutely sure without knowing the full context of the sentence. But I think it's fine to use Nobody could ... to mean impossibility in the present because it uses could – not couldn't. If we make a version of the sentence using couldn't:
It isn't equivalent in meaning. It would be understood as referring to a past ability, not a present possibility. As you've seen above, could and couldn't have nuances in their meanings and aren't exact opposites, so could with a negative subject (e.g. Nobody could) isn't the same meaning as couldn't (for the meaning of possibility, at least).
For other meanings, could and couldn't may be more direct opposites. The sentences below about ability do have the same meaning.
Does that make sense?
Best wishes,
Jonathan
The LearnEnglish Team