modals + have

We use a modal verb with have and the past participle:

 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.