Past modals of deduction

Rules

• Rule 1: must have + V3 = it surely happened

  When there's strong evidence and we're sure something happened, we use must have + V3.

  Pattern: subject + must have + V3

  Example: Kaan has a medal around his neck. He must have won the race.

  Example: The plates are empty. The guests must have enjoyed the meal.

• Rule 2: can't have + V3 = it can't have happened

  When we're sure something was impossible, we use can't have (or couldn't have) + V3. (In American English *must not have + V3* is also used for a negative guess: *He must not have seen us.* But for “definitely not”, can't have is the safest choice.)

  Pattern: subject + can't / couldn't have + V3

  Example: Selin can't have taken the bus. She was at home all day.

  Example: You can't have finished that book already! It's 500 pages long.

• Rule 3: might / may / could have + V3 = maybe it happened

  When we're not sure and something maybe happened, we use might / may / could have + V3.

  Pattern: subject + might / may / could have + V3

  Example: Zehra is late. She might have missed the bus.

  Example: I can't find my scarf. I may have left it on the train.

• Rule 4: could have + V3 = possible, but it didn't happen

  could have + V3 also describes something that was possible but didn't happen: a missed chance, or something that luckily didn't happen.

  Pattern: subject + could have + V3 (but it didn't)

  Example: We could have gone to the beach, but we stayed at home.

  Example: You could have called me! I was waiting.

• Rule 5: should(n't) have + V3 = regret / criticism

  For a past mistake, we use should have + V3 (you should have, but you didn't) or shouldn't have + V3 (you shouldn't have, but you did). In speech have is shortened: *must've, should've* (but never write ~~must of~~!).

  Pattern: subject + should / shouldn't have + V3

  Example: I should have charged my tablet. Now the battery is dead.

  Example: We shouldn't have left the cake in the sun. Now it's soft.

Common mistakes

• She must have went home. → She must have gone home.

  After have, use the V3: go – went – gone.

• I should studied more. → I should have studied more.

  For the past: should have + V3.

• It must rained last night. → It must have rained last night.

  A past guess: must have + V3; don't forget have.