Combine must, might, may, can’t, or couldn’t with have been plus the -ing form to speculate about an action that was ongoing at a past moment, as in she must have been sleeping when the fire alarm went off. Must have been shows strong certainty, might/may have been shows possibility, and can’t/couldn’t have been shows strong certainty it’s untrue.
Grammar Rule
These modals combine with have been + -ing to speculate about an action that was ongoing at a past moment.
Past Modals of Deduction (Continuous): Rules and Examples
| Modal | Certainty | Example |
|---|---|---|
| must have been + -ing | strong certainty | She must have been sleeping when the fire alarm went off. |
| might/may have been + -ing | possibility | They might have been waiting outside for over an hour. |
| can’t/couldn’t have been + -ing | strong certainty it’s untrue | He can’t have been working all night; he looks far too energetic. |
Remember: modal + have been + -ing, for deduction about an action in progress at a past moment.
Practice Test
Instructions
Answer each question in the test below forming the correct past deduction with a continuous form. 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.
Advanced Past Modals of Deduction
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Frequently Asked Questions
How do you speculate about an action in progress in the past?
Use a modal plus have been plus the -ing form, as in she must have been sleeping when the fire alarm went off.
What does must have been + -ing express?
Strong certainty that something was happening, as in she must have been sleeping when the fire alarm went off.
What does might have been or may have been + -ing express?
A possibility, as in they might have been waiting outside for over an hour.
What does can’t have been or couldn’t have been + -ing express?
Strong certainty that something was not happening, as in he can’t have been working all night, he looks far too energetic.