Modal verbs for past speculation

• What this is about
• Must have
• Might have / may have
• Could have
• Should have / shouldn't have
• Can't have
• Summary table

What this is about

We have already learned modal verbs for the present: can, must, should, may, might. Now we'll learn how to use them to talk about the past. We combine a modal verb with have + past participle.

Must have

Must have + past participle is used when we are almost certain something happened:

She must have forgotten. => I'm almost sure she forgot.

He's not here. He must have left early.

They must have been very tired after the trip.

Might have / may have

Might have or may have + past participle is used when something is possible but we're not sure:

He might have gone home. => It's possible.

She may have missed the bus.

They might not have received the email.

Could have

Could have + past participle is used for past possibilities - things that were possible but didn't happen:

We could have won the game. => But we didn't.

You could have told me!

She could have become a doctor. => But she chose something else.

Should have / shouldn't have

Should have + past participle is used for regret or criticism about the past - things that were the right thing to do but didn't happen (or vice versa):

You should have called me. => But you didn't.

I shouldn't have eaten so much. => But I did.

We should have left earlier.

She shouldn't have said that.

Can't have

Can't have + past participle is used when we are almost certain something did NOT happen:

She can't have said that. She's too polite.

He can't have finished already. He only started ten minutes ago.

Summary table

must have + pp => almost certain it happened (deduction)

might have / may have + pp => possible but not sure

could have + pp => was possible but didn't happen

should have / shouldn't have + pp => regret / criticism

can't have + pp => almost certain it didn't happen