We use a modal verb with have and the past participle:
|Jack and Jill||would||have||been||late|
We use a modal verb with have to refer back:
- … from a point of time in the past:
We were very worried. Someone might have taken the car.
- … from the present
It is nearly eight o’clock. They will have arrived by now.
- …or from the future:
We won’t eat until they arrive. They might not have had supper.
- or to refer to past time:
You should have helped her when she asked.
They might have got lost. Nobody knows where they are.