Past Tense Modals

Past tense modals talk about past possibilities, guesses, regrets, and missed opportunities.

Form

Use a modal + have + past participle.

Meaning	Form	Example
strong positive guess	must have	She must have forgotten.
strong negative guess	can’t have / couldn’t have	He can’t have seen us.
possible past	may have / might have / could have	They might have left early.
missed opportunity	could have	We could have taken a taxi.
past advice	should have	You should have called.

Must Have And Can’t Have

Use must have when evidence makes you almost sure.

The ground is wet. It must have rained.

Use can't have or couldn't have when something seems impossible.

She can't have received the email. She would have replied.

Might Have, May Have, Could Have

Use these when something was possible, but you are not sure.

He might have gone home.

You could have left your phone in the car.

Should Have

Use should have for a good idea in the past that did not happen.

I should have studied more.

Use shouldn't have for a past action that was not a good idea.

You shouldn't have told him.

Common Mistakes

Avoid	Use
She must has forgotten.	She must have forgotten.
He might left early.	He might have left early.
You should called me.	You should have called me.

Practice

1 / 6

The lights are off. They must have ___ home.

AgoneBisCwasDhas

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Summary

Use modal + have + past participle for past meanings. Must have shows a strong guess, can't have shows a strong negative guess, might/may/could have show possibility, could have can show a missed opportunity, and should have gives advice about the past.