We use modals for a range of different reasons. Here we look at must, might, may, could, can’t and couldn’t and see how to use them.
must have (past)
Must have + past participle is used when we are sure about something.
It must of been John who organised the party
It must have rained last night, look at the water!
might have / may have (past)
Might have / may have + past participle is for situations that you are not 100% sure about.
I think I might have left the oven on, let’s go back and check.
There may have been an accident this morning.
We can also use could have in this context.
can't have / couldn't have (past)
Can’t have / couldn’t have + past participle is used for situations we think didn’t happen.
She can’t have made all those cakes, she doesn’t have an oven.
I couldn’t have been there, I was in Ireland at the time.
We use must for situations that we are sure about.
This must be the correct answer, all the others are wrong.
I must run the fastest in the team.
might, may, could (present)
Might, may or could are used in situations we are not totally sure about.
I think the weather might be good tomorrow.
He may be a little late today.
It could be difficult to complete in that time.
May is more formal than might and could.
Can’t is used when we are sure something is not possible
It can’t be done before the weekend.
I can’t run that fast
He can’t come in today, it’s his day off