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'can' and 'could'

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

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can and could: possibility 2

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can and could: other uses 1

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can and could: other uses 2

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Comments

Hi I want to ask about usage of '' Must not'' negative form of Must in past Can I use ''Mustn't have v3'' in Past strong advice and past prohibited.For exapmle can I say ''Last night you was sic.You must not have gone to outside'' (Strong advice) and talk about past prohibited can I say ''You mustn't have sold cigarette under 18 20 years ago'' ? İt may be still forbidden or not now.But that time it was forbidden.Last question Can I use ''must have '' past advice like ''should have'' for example can I say ''you failed exam you must have studied hard'' otherwise can I use ''mustn't have done'' only past strong deduction ? For Exapmle: I saw my friend's car in front of his home and I can say 'He mustn't gone work by his car''

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

These animals can be dangerous. - Is it the same as These animals may be dangerous?

Many thanks.

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

Could is use for past ability and for possibility, how we can know in what meaning could is used for in sentence

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:

  • She could speak several languages.

But, in real speaking or writing, it would have more context, for example:

  • Sara's so good with languages. Even when she was little, she could speak several languages.

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

Yes, but what about below example
You :- Sarah can speak English?
Me :- she Could (as I'm not 100% sure about answer)

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

Hi English Team,

Hope you are doing well. I have a few Qs

1. There are three possibilities: we can talk to a lawyer, we can go to the police, or we can forget all about it (How about 'could'?)

2. What shall we do? We can try asking Lucy for help (How about 'could')

3. What shall we do tomorrow? Well, we could go fishing (How about 'can')

4. This success could not have been achieved without your cooperation. (How about 'cannot have')

Thanks so much.

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

 

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