Thursday, 19 July 2012

Modal Verbs: Can

The Forms, Meanings and Use of the Modal Verb CAN (COULD).

Can and could are modal auxiliary verb, like for example must, may and should. Like other modal verbs, 'can' has no –s on the third person singular (he can, not he cans); questions and negatives are made without do (Can I?, Could I? not Do I can?, Did I could?); these verbs are followed by the infinitive without to (e. g.: I can do it.). 'Can' and 'could' have no infinitive or participles (to can, canning do not exist).

Patterns. Read and memorize! 
Affirmative Interrogative Negative
I can swim.Can I swim? I cannot swim.
He can swim.Can he swim? He cannot swim.
She can swim.Can she swim? She cannot swim.
It can swim.Can it swim? It cannot swim.
We can swim.Can we swim? We cannot swim.
You can swim.Can you swim? You cannot swim.
They can swim.Can they swim? They cannot swim.
Note 1: - the modal verb 'can' has only two forms – can in the present and could in the past. The missing tense is supplied by the future of to be able.
E. g. : I shall be able to prepare for my exams.

Note 2: - There are contracted negative form can’t, couldn’t.
E. g.: I can’t understand.

Be careful about the pronunciation of 'can’t': in British English it has a quite different vowel from 'can'.
Can [kᴂnt]; can’t [kɑːnt] (GB), [kᴂnt] (US).


The modal verb CAN expresses:
1). physical ability

Key examples:
  1. Tom can lift heavy boxes.
  2. Tom can run long distance.
  3. Tom can climb high mountains.

 2). mental capacity
  1. Helen can read French books in the original.
  2. Helen can recite poems beautifully.
  3. Helen can speak many foreign languages.

3). permission or possibility
  1. You can join our circle.
  2. You can take part in the work of the club.
  3. You can choose a theme for your investigation.
  4. You can find some books on this topic.
  5. You can prepare a report by March.
  6. You can consult our professor.

3). supposition, doubt, uncertainty or disbelief (in interrogative or negative sentences).

can + Indefinite Infinitive (or Continuous Infinitive)

  1. Can John be 16 years old? He is a student already.
  2. Can he be planning this research? It is not in his line.
  3. Can it be stormy today? The forecast was good.
  4. Can it be raining today? It cannot be raining. The sky is cloudless.
Note: - The Indefinite (or Continuous) Infinitive refers the action to the present and future.

can + Perfect Infinitive

  1. Lanny can’t have hurt Helen. He is a very kind man and they are on friendly terms.
  2. Lanny can’t have spoken rudely. He is very polite.
  3. Lanny can’t have acted this way. I have known him for many years.
  4. Lanny can’t have deceived Helen. He is honest.
  5. Lanny can’t have offended Helen. He is a tactful man.
Note: - The Perfect Infinitive refers the action to the past.


Meaning: Could is used for 'general ability', to say that you could do something any time you wanted to. (Was/were able to is also possible).

E. g. :  My father could speak six ten languages.


Could + Perfect Infinitive

Sometimes 'could' is used to say that we had the ability to do something, but we did not try to do it. There is a special structure for this: could have + past participle . This structure also can be used to criticize people for not doing things.
E. g. :
You could have helped me! (= You were able to help me – why didn’t you?)
You could have told me you had invited people to dinner. (= Why didn’t you tell me …?)

Note: 'Can' and 'could' are both used with the perfect infinitive (have + past participle) for speculating and guessing about the past. 'Can' is only used in negative sentences and questions.
  • Where can she have gone
  • She can’t have gone to school – it’s Sunday. 
  • She could have gone off with some friends. (Not She can have gone ...) 

► 'Could' is not only the past of 'can'. This verb can be used to talk about the present and the future.
  • You could be right. 
  • Could I see you tomorrow? 

► 'Could' also has a conditional use.
  •  I could marry him if I wanted to.
  •  I could have won if I hadn’t fallen over.