Modal Verbs of DEDUCTION

Hi English learners. Welcome to a new lesson. We will talk about the modal verbs of deduction: may, might, could, can’t, must.

We talk about deduction when we use the available information to say how certain we are about something. The modal verbs we use to indicate the level of certainty are:




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Modal verbs of deduction: may/might/could

We can use the modal verbs may, and might when we think that something is not certain.

  • Sara is not at home. Where is she? She may be at work. She might be in the supermarket. 
  • I’ll ask the neighbour. He may know where she is.
  • I’m coming, but I might be a few minutes late.
  • Susan is not answering the phone. She may be sleeping.

Learn more about the modal verbs may and might on this link

You can use could in the same way.

  • Monica hasn’t arrived to work yet. She could be stuck in traffic.
  • The hotel could hire more staff, but nothing is sure yet.
  • Mildred could be interested in working abroad.

The modal verb of deduction: can’t

We can use the modal verb can’t when we are sure that something is impossible.

  • They can’t be at home. The lights are out.
  • Peter can’t know many people here. He’s just moved in.
  • He can’t be a rich man, living in that shabby house.

The modal verb of deduction: must

We normally use the modal verb must when we are sure that something is true.

  • He must have a lot of money, driving that expensive car.
  • Sandra is not at home. She must be at the gym.
  • David must be feeling unhappy after his parents got divorced.

Modal verbs of deduction in the past

To use the modal verbs of deduction in the past you can use the structure 

May/might/could/can’t/must + have + past participle
  • Susan is not in her office. She may have gone for lunch.
  • Martin wasn’t answering his phone when I called him earlier. He might have been busy.
  • I can’t find my wallet. I could have left it at work.
  • I can’t have forgotten to lock my car because it was locked.
  • The man we saw in the street was looking at the map. He must have been a tourist.

Do the exercise to perfect your knowledge:

  1. There was a lot of noise coming out of neighbour’s house last night. They __________ (must / have) a party.
  2. I can’t find my phone. I ________ (might/leave)
  3. Nobody is answering the phone. They ________ (must/be)
  4. They left a few minutes ago. They ______ far. (can’t/be)
  5. You’ve been working all day. You _____ exhausted. (must/fell)
  6. That man can’t speak English. He  ______ be a foreigner. (might/be)

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Download the worksheet about modal verbs of deduction

Answer key:

1) must have had 2) might have left 3) must be 4) can’t be 5) must feel 6) might be

Modal verbs of deduction
Modal verbs of deduction

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