- To make someone do something
- To be compulsory.
Obligations imposed by the speaker
You must brush your teeth before you go to bed
Have to/Have got to
Obligations not imposed by the speaker
I´ve got to do some homework tonight (my teacher says so)
I have to do some homework tonight
Past and reported obligations
We were told we had to get a visa before we left on holiday
Should do/Ought to
No difference in meaning
You ought to/should write home more frequently
Should have done/Ought to have done
For criticism or regret, because an action didn´t happen.
We should have bought/ought to have
bought your sister a car for her birthday
ASKING FOR AND
- To allow someone to do
- To permit someone to do
- To let someone do
Can: More usual
Could: a bit more polite
May: Quite formal
Can/May/Could I borrow your bike?
Yes, you can/may
- To forbid someone to do something
- To ban someone from doing something
. To not allow someone to do something
- To not permit someone to do something
- To not let someone do something
- Don´t cycle on the pavement!
When something is forbidden
You musn´t cross the road without looking
Eliza can´t go out this evening (her father says so)
Was not to/Couldn´t
Speculate about something the speaker in unsure
I could be a sea eagle, though the feathers look too dark
The car must be doing eover 50 mph at least!
Certainty, in relation to impossible ideas and situations
They couldn´t possible be here before lunchtime
Questions, to speculate about something
Couldn´t it be a computer error?
Uncertainty, in the past
Could have/Might have/May Have
I think I may have met you before
Certainty that something in the past was impossible or didn´t happen
Couldn´t have/Can´t have
It can´t have been raining, as the path is completely dry
Near-certainty about something in the past
It must have been cold that winter
MAKING A SUGGESTION
It´s time.../It´s about time.../It´s high time...
Always in simple past, even when we are talking about the present or the future
- It´s time you went to bed (you need to go to bed now)
Infinitive with "to" after "it´s time...", if we are speaking in general termsIt´s time to go (everybody needs t go now)