8. Expressing ability and inability

Can is an auxiliary verb. We use can to:

 

- talk about possibility and ability
- make requests
- ask for or give permission

 

The main verb is always the infinitive.

 

 

 

Use of can
 
Possibility and Ability

 

We use can to talk about what is possible, what we are able or free to do:

 

Normally, we use can for the present. But it is possible to use can when we make a decisions about the future.

 

 

We often use can in a question to ask somebody to do something. This is not a real question - we do not really want to know if the person is able to do something, we want them to do it! The use of can in this way is informal (mainly between friends and family).

 

 

We sometimes use can to ask or give permission for something.

 

(Note that we also use could, may, might for permission. The use of can for permission is informal.)

 

 

Although we look at be able to here, it is not a modal verb. It is simply the verb be plus an adjective (able) followed by the infinitive. We look at be able to here because we sometimes use it instead of can and could.

 

We use be able to to talk about ability.

 

Structure of be able to: subject + be + able + infinitive

 

 

  

  

  

We use be able to to express an ability. "Able" is an adjective meaning: having the power, skill or means to do something. If we say "I am able to swim", it is like saying "I can swim". We sometimes use "be able to" instead of "can" or "could" for an ability. "Be able to" is possible in all tenses - but "can" is possible only in the present and "could" is possible only in the past when refering to an ability.