Modals of Deduction (Past)

• When we want to guess about something that happened in the past, we use modals of deduction. We choose the modal depending on how sure we are about our guess.
• Modal
• Meaning / Certainty
• Example
• must have + past participle
• Almost certain it happened (logical conclusion)
• He must have crashed into the pole.
• might have / could have + past participle
• Possible it happened (uncertainty)
• She might have left a note on the windscreen.
• can't have / couldn't have + past participle
• Almost certain it didn't happen (impossible)
• They couldn't have seen the security camera footage.
• Remember
• Use must have when you have strong evidence for a past event.
• Use can't have or couldn't have when you are sure a past event was impossible.
• Use might have or could have for possibilities in the past.
• Always follow the modal verb with 'have' and a past participle.
• Examples
• The car has a massive dent, so someone must have backed into it.
• Jessica can't have driven the car because she was in Boston.
• Mark might have forgotten his keys in the Chicago office.
• Common mistakes
• He must hit the other car.
• He must have hit the other car.
• They can't has seen the sign.
• They can't have seen the sign.

Complete the sentences

• The bumper is completely broken. Someone (must hit) ____ it yesterday.
• Emily wasn't in Seattle yesterday. She (can be) ____ the driver.
• Brian's car was dirty, so he (might wash) ____ it later.
• Sarah didn't see the truck. She (could look) ____ at her phone.
• Kevin's keys are missing. He (must leave) ____ them in Austin.
• The doors were locked. The thief (could enter) ____ through the front.

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