Definition can in British English

Can is usually followed by an infinitive without ‘to’: I can speak French. Sometimes it is used without a following infinitive: Come and help us, if you can.

Can does not change its form, so the third person singular form does not end in ‘-s’: She can speak Japanese.

Questions and negatives are formed without ‘do’: Can you swim?

The negative form of can is cannot: We cannot allow this behaviour to continue. Cannot is often shortened in conversation or informal writing to can’t: I can’t find my brown jacket.

Can is often used in question tags: They can’t hear us, can they?

Can has no participles and no infinitive form. Be able to is used as the infinitive to show ability or possibility: I want to be able to choose my own career.

Could is used as the past tense of can when it means that someone had the ability to do something, or that something was possible: New York was a place where anyone could start a business. But was/were able to is used for saying that someone actually succeeded in doing something: By climbing on the table he was able to reach the window.

There is no future tense of can, but will be able to is used for saying that someone will have the ability to do something or that something will be possible in the future, especially after a long time: She’ll be able to walk soon.A hundred years from now people will be able to visit Mars. Can is usually used when planning or deciding about the near future: We can go shopping tomorrow.

There is no perfect tense of can, so has/have been able to is used: I haven’t been able to phone my parents yet.

The negative form of the verb can is cannot. It is written almost always as one word, not as ‘can not’ (two words):

? The quality of the information can not be guaranteed.

✓ The quality of the information cannot be guaranteed.

? You can not buy true friends or health.

✓ You cannot buy true friends or health.