must be, might be, can’t be

Examples

1. Her car is outside, so she must be at home.

2. He might be on his way already.

3. That can’t be the right address.

4. She may not know about the change.

Common mistakes

• ✗Wrong: She must not be at home, the lights are off.

  ✓Right: She can’t be at home, the lights are off.

  The confident negative conclusion is can’t be; must not means forbidden.

• ✗Wrong: He must to be tired.

  ✓Right: He must be tired.

  A modal is followed by the base verb with no to.

• ✗Wrong: Maybe he can be at work.

  ✓Right: He might be at work.

  can states an ability; might states a possibility.

Practice questions

Try each one yourself first, then open “Show answer” for the solution and the reason.

1. 1Choose the correct sentence.

   1. AYou have been walking for hours — you must being exhausted.
   2. BYou have been walking for hours — you must to be exhausted.
   3. CYou have been walking for hours — you must be exhausted.
   4. DYou have been walking for hours — you can be exhausted.
   Show answer

   Answer: C You have been walking for hours — you must be exhausted.

   Strong evidence, so a confident conclusion with must be.

2. 2Choose the correct sentence.

   1. AIt can’t be Sara — she is in Spain this week.
   2. BIt must not be Sara — she is in Spain this week.
   3. CIt is not can be Sara — she is in Spain this week.
   4. DIt can’t to be Sara — she is in Spain this week.
   Show answer

   Answer: A It can’t be Sara — she is in Spain this week.

   Confident that it is impossible: can’t be.

3. 3Choose the correct sentence.

   1. AI am not sure — she might have my number.
   2. BI am not sure — she must have my number.
   3. CI am not sure — she can have my number.
   4. DI am not sure — she might to have my number.
   Show answer

   Answer: A I am not sure — she might have my number.

   might is the honest middle when you do not know.

4. 4Choose the correct sentence.

   1. AThey must not have got the letter, I am only guessing.
   2. BThey can not have receive the letter yet as a guess.
   3. CThey might not to have received the letter.
   4. DThey may not have received the letter.
   Show answer

   Answer: D They may not have received the letter.

   may not says it is possible that they did not.

5. 5Fill in the gap.

   The office is dark, so everyone _____ gone home.

   1. Amust have
   2. Bcan have
   3. Cmust to have
   4. Dmight not have
   Show answer

   Answer: A The office is dark, so everyone must have gone home.

   Dark windows are strong evidence, so must.

6. 6Fill in the gap.

   I _____ be wrong, but I think the shop shuts at five.

   1. Amust
   2. Bcan’t
   3. Cmight
   4. Dam able to
   Show answer

   Answer: C I might be wrong, but I think the shop shuts at five.

   Hedging your own claim takes might.

7. 7Fill in the gap.

   That _____ be his brother — they look identical.

   1. Acan’t
   2. Bis must
   3. Cmust
   4. Dmay not
   Show answer

   Answer: C That must be his brother — they look identical.

   Looking identical is evidence for a confident yes.

8. 8Fill in the gap.

   She _____ be forty — she was in my class at school.

   1. Acan’t
   2. Bmust
   3. Cmay
   4. Dmight
   Show answer

   Answer: A She can’t be forty — she was in my class at school.

   Knowing her age makes the claim impossible.

9. 9Put the words in the right order.

   He might be stuck in traffic

   Show answer

   Answer: He might be stuck in traffic.

   Modal + base verb, with no to between them.

10. 10Put the words in the right order.

    That can’t be the right platform

    Show answer

    Answer: That can’t be the right platform.

    can’t be is the confident negative.