Use must have plus the past participle for a strong conclusion that something happened, as in she must have missed the bus, can’t have for a strong conclusion that it didn’t happen, and might have, may have, or could have for an uncertain possibility about the past. These modals make logical conclusions about the past.
Grammar Rule
Modal + have + past participle makes logical conclusions about the past, with different degrees of certainty.
Modals of Deduction (Past): Rules and Examples
| Modal | Certainty | Example |
|---|---|---|
| must have | strong certainty it happened | She must have missed the bus. |
| can’t have | strong certainty it didn’t happen | He can’t have finished already. |
| might/may/could have | uncertain possibility | They might have forgotten about the meeting. It could have been an accident. |
Remember: modal + have + past participle for deductions about the past.
Practice Test
Instructions
Answer each question in the test below using the correct modal of deduction for the past. You will get a new random set of questions every time you retake the test, plus a downloadable results summary with your name and score at the end.
Modals of Deduction – Past
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Frequently Asked Questions
How do you express near certainty about something in the past?
Use must have plus the past participle, as in she must have missed the bus.
How do you express that something almost certainly didn’t happen?
Use can’t have plus the past participle, as in he can’t have finished already.
Which modals express uncertain possibility about the past?
Might have, may have, and could have, as in they might have forgotten about the meeting.
What is the structure after these modals?
Have plus the past participle, the same structure for every subject, as in it could have been an accident.