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Can

Can: forms​

Affirmative (+) form​

Can comes first in the verb phrase (after the subject and before another verb):

  • We [verb phrase] can take the train to Birmingham.

Can is never used with another modal verb:

  • He can hear the music from his room sometimes.
  • Not: He can might hear the music … or He might can might hear the music …

Negative (−) form​

The negative form of can is can’t. We don’t use don’t/doesn’t/didn’t with can:

  • I can’t believe you said that!
  • Not: I don’t can believe you said that!

We can use the full form cannot (one word) in formal contexts or when we want to emphasise something:

  • I cannot understand why she behaves like that.
See also
  • Modality: forms

Question (?) form​

warning

The subject and can change position to form questions. We don’t use do/does/did:

  • Can this really be true?
  • Not: Does this can really be true?
  • Can’t you ask for another day off work?

We use can and can’t in question tags:

  • You can’t take photos inside the museum, can you?
  • Abby can speak Japanese, can’t she?

Can: uses​

Permission​

We often use can to ask for or give permission:

  • Can I take Daisy for a walk?
  • Students can use calculators during the exam.

We use can’t to forbid (say what you must not do):

  • You can’t park there.
  • You can’t just take the day off work. You have to have permission in advance.
See also
  • May

Ability​

We often use can to talk about ability to do something in the present or future:

  • I can sing one song in Polish.
  • Can you sleep on your back?
  • We can go swimming after school tomorrow, if you like.

We often use can with verbs of perception such as hear, see, smell, taste, and mental process verbs such as guess, imagine, picture, understand and follow (in the sense of ‘understand’):

  • I can hear you.
  • I can see her coming down the road now.
  • Can you smell something burning?
  • I can guess why you’re angry.
  • We can’t follow these instructions for installing this new DVD player. (We can’t understand these instructions.)

General truths​

We use can to talk about things which we think are usually, but not always, true:

  • Reducing cholesterol through diet can be difficult. (It’s not always difficult for everyone, but in general it is difficult.)
  • Fireworks can frighten pets.
  • Swans can be very vicious.

We don’t normally use could to talk about what we believe to be true in the present.

Compare

Exercise can help reduce stress.I believe this is a general truth or fact.
Exercise could help reduce stress.I see this only as a possibility.
Finding a hotel in August can be difficult.I believe this is a general truth or fact based on my experience or knowledge.
Finding a hotel in August could be difficult.I see this only as a possibility.
See also
  • Could

Possibility​

We use can to express possibility or to question possibilities:

  • We can go to Rome in June because both of us have a week off work. (It is possible for us to go to Rome because we don’t have to work in June.)
  • Well, how can you be on a diet if you buy so much chocolate? (I don’t think it’s possible that you are on a diet because you still buy lots of chocolate.)

Guessing and predicting: can’t as the negative of must​

When we want to guess or predict something, we use can’t as the negative form of must. We use can’t have + -ed form as the negative form of must have + -ed. Can’t and can’t have + -ed form express strong possibility:

  • A: Who owns this blue coat? It must be yours.
  • B: It can’t be mine. It’s too big. (A uses must to guess that the coat belongs to B. He sees this as a strong possibility. B uses can’t to express strong negative possibility. The coat is too big, so it isn’t his.)
  • A: Roy must have made a lot of money.
  • B: He can’t have done. He doesn’t even own a house. (A makes a deduction that Roy has made a lot of money. B sees this as very unlikely and so expresses it as a negative possibility.)
See also
  • Must
  • Could

Requests​

We use can as a question form to make requests:

  • Those cakes look so good. Can I try one?
  • Can I have your surname?
  • Can you help me with this form?
See also
  • Could
  • Requests

Reproaches​

We use can’t as a question form to ask people to stop doing something we don’t want them to do, or to do something they are not doing which we want them to do:

  • Can’t you stop making that awful noise?
  • Why can’t you just be nice to her instead of upsetting her?

Offers​

We use can as a question form to make offers:

  • Can I help you lift that?
  • Can we do anything for you?
See also
  • Offers

Can: past​

The past of can is could:

  • In those days, you could buy everything in the local shop. Now we have to go to the big supermarket for everything.
  • We asked the security guards if we could go backstage to meet the band.

When we question the possibility of something in the past, we use can’t have +-ed form:

  • You can’t have arrived here earlier than me.

Can: typical errors​

We write cannot as one word:

  • The children cannot be left unsupervised at any time.
  • Not: The children can not be left unsupervised …

We use could, not can, to talk about ability in the past.

  • They could see a light on in the house as they drove past at 10 pm.
  • Not: They can see a light on in the house …