We can use modal verbs to talk about ability (either general ability or specific ability in a particular situation). The modal verbs of ability are ‘can’, ‘could’, and ‘be able to’. Ability can be expressed in the past, present, or future.
Ability in the present
‘Can‘ is a modal verb that describes what someone is able to do, i.e. general ability in the present. It is used in different forms to describe past and present abilities.
- Peter can cook Italian food.
In positive statements we put ‘can‘ between the subject and the main verb in its base form:
subject + can + the verb (infinitive without ‘to’)
- I can ride a bicycle.
- They can help you with building your house.
The negative form of ‘can‘ becomes ‘can not’ or contracted ‘cannot’ (‘can’t’):
- Jeffrey cannot play the piano.
- She can’t go with us because she’s sick.
Questions with ‘can‘ are formed by swapping the subject and the modal verb:
Can + subject + the verb (infinitive without ‘to’)
- Can Jane play tennis?
- Can he drive a car?
Ability in the past
To talk about ability in the past we use ‘could‘, which is the past form of ‘can‘.
- I can’t dance rumba now (present ability), but I could when I was younger (past ability).
- I could read when I was four.
The negative form of ‘could‘ is ‘could not (couldn’t)’. ‘Couldn’t‘ can be used to describe general and specific ability in the past:
- I couldn’t go to that restaurant because it was too expensive. (general ability)
- My grandfather couldn’t swim. (general ability)
- He called us because he couldn’t find the house. (specific ability)
- I couldn’t open the window. (specific ability)
Was able to
To talk about for specific ability in a particular situation in the past we can also use ‘was able to‘. The negative form of ‘was able to‘ is ‘wasn’t able to’ or ‘was unable to‘.
- When the computer crashed yesterday, I was able to fix it. (not ‘I could fix it’)
- She was able to pass the exam, even though she hadn’t studied much. (not ‘she could pass’)
Could have + Past Participle
To talk about an ability someone had in the past, but didn’t use, we can use ‘could have + Past Participle‘:
- I could have passed the test well but I didn’t practise enough.
- He could have come earlier.
Ability in the future
We don’t use ‘can‘ to describe general ability in the future. Instead, we use ‘will be able to’:
- Peter can play the accordion quite well (present ability). In a year or two he will be able to give concerts (future ability).
- Next Sunday I will be able to see the new fountains in the park.
Negative statements about future ability are formed using ‘won’t be able to’ or ‘will be unable to’:
- If you don’t study well, you won’t be able to find a good job.
- Sorry, I’ll be unable to call him at 2 PM. I’ll be in a meeting at that time.
BUT sometimes we can use ‘can‘ to describe a specific future ability:
- I can help you tomorrow.
- I can’t come to the party.
Watch this video from mmmEnglish to see how the modal verbs of ability are used: