| FUNCTION
| VERB
| INFINITIVE
| USAGE
| EXAMPLES
|
| ability, capability
| can
| simple
| reference is made to the present and future
| I can play chess.
We can go for a walk in the evening.
|
| could
| simple
| reference is made to the past
| I could spend more time with my friends before.
|
| simple
| to express unreality with reference to the present and future
| She has very nice pronunciation. She could help you to improve your phonetics.
|
| simple
| reference is made to the past, and we don’t know whether the action was fulfilled
| She could help him.
|
| perfect
| reference is made to the past, and the action wasn’t realized
| She could have called Jim to inform him about the cancellation of the meeting.
|
| be able to
| simple
| time reference is not clear from the context or we need to stress that the action refers to the future
| He’ll be able to phone us from home.
He’ll be able to buy the car he wants just in a few months.
|
| simple
| reference is made to the past, and we know the action was realized
| Carol was able to suggest her own way out of this situation.
|
| achievement
| be able to, manage
| simple
|
| I was able to complete the work.
|
| advice
| can
|
|
| You can ask Mary.
|
| could
|
|
| You could ask Mary.
|
| ought to obligation (advisability, desirability)
| + / -- / ?
| simple
| reference to the future
| You ought to visit granny.
|
| simple / continuous
| reference to the present (stative / durative verbs)
| You ought to be studying hard.
|
| +
| perfect
| desirable action wasn’t fulfilled
| You ought to have kept this secret to yourself.
|
| --
| perfect
| undesirable action was fulfilled
| You oughtn’t to have shouted at your mother.
|
| should
| + / -- / ?
| simple
| reference to the future
| We should discuss the matter over.
|
| simple / continuous
| reference to the present (stative / durative verbs)
| You should be doing up accurately.
|
| +
| perfect
| desirable action wasn’t fulfilled
| You should have accepted the offer.
|
| --
| perfect
| undesirable action was fulfilled
| You shouldn’t have bought this awful sofa.
|
| might
| simple
|
| You look tired. You might ask her for help.
|
