Ability
Can: something is possible, someone has an ability --> Natasha can play the piano.
Could:
ability or opportunity in the past --> Natasha could play the piano when
she
was
four.
Be able to:
an
ability or opportunity resulted in a particular action --> The plane was able to take off at eleven o’clock after the fos had lifted.
Permission
Can:
informal-->
Can I use your
pen?
Could:
polite --> Could we borrow your ladder, please?
May:
formal -->
May
I see
the
letter?
Be allowed to: Permission resulted in a particular action --> I was allowed to leave work early yesterday.
Possibility and certainity
May:
low
possibility
Might:
lower
possibility
Could:
possible
Must:
something is certainly true -->
She
isn’t
answering the phone. She must be out.
Can’t:
something is impossible --> We haven’t walked far. You can’t be tired yet.
Necessity
Must:
the
speaker feels
that
something is necessary --> You must think about your future. (I’m telling you.)
Have to:
the
situation makes something necessary --> We have to be quiet (that’s the rule.)
Mustn’t: something is a bad idea -->
You
mustn’t forget my key, or I won’t get in.
Needn’t: something is not necessary --> You needn’t was those glasses, they’re clean.
Don’t have to
and don’t need to: same meaning as needn’t.
Didn’t need to: something was not necessary --> Mark didn’t need to hurry because he had lots of time.
Needn’t have: something we did which we now know was not necessary --> We needn’t have gone to the supermarket. We already had a pizza for
tonight.
Advice
Should: what is the best thing or the right thing to do. --> You’re not very well. Perhaps you should see a doctor.
Ought to:
what
is
the
best
thing
or
the
right
thing
to
do. -->
Your
uncle
was
very
kind
to
me. I ought
to
write
him
a letter of thanks.
Had better: to say what is the best thing to do in a situation. --> It’s cold. The children had better wear their coats.
Be supposed to: talking about the normal or
correct way of doing things. --> The guests are supposed to buy flowers for the hostess.
Modal Perfects
We use the Modal + a present perfect to talk about advice, possibilities, etc in the past.
Could (possibility): The captain could have tried to to fight the pirates.
Should (advice): They should have caught the pirates.
Must (we think something was true): The experience must have been terrible.
May/might (low possibility): A real government might / may have prevented piracy.
