Modals of Obligation


What are modals of obligation?

  • We use modals of obligation to discuss responsibilities and to give advice.

  • The three most common modals of obligation are must (strong obligation), have to (strong to medium obligation) and should (weak obligation).

    • I must take my father to the hospital right now!

    • I have to go to work tomorrow.

    • I should clean my room.

How do we use modals of obligation?

  • Must

    • We use “must” to express a strong obligation which usually comes from the speaker themselves.

      • I am sick all the time! I must stop smoking.

      • My mother misses me. I must call her tomorrow.

    • Be careful when negating “must.” “Mustn’t” refers to something that is not allowed or something that shouldn’t be done. (You mustn’t smoke in the hospital.) If you want to show a lack of obligation, you need to use “don’t have to.”

      • You don’t have to stop smoking now. Why don’t you wait until next week?

      • I don’t have to call my mother, but I want to.

  • Have to

    • We use “have to” when we are talking about strong obligations that come  from someone else, not the speaker. This usually refers to a rule or a law.

      • My mom said I have to clean my room tomorrow.

      • She has to start paying attention in class.

      • We have to talk about our taxes.

      • I don’t have to go to work tomorrow. Let’s play tennis instead!

  • Should

    • We use “should” when we are referring to weak obligations or when we are giving advice.

      • You should stop smoking.

      • We should call grandma today, it would make her very happy to hear our voices.

      • She shouldn’t talk during class.


I. Fill in the blank with the correct modal of obligation

  • The concert isn’t free. You _______ pay to get in.

  • You _______ run with scissors.

  • Children ________ never talk with their mouths full.

  • I ______ go to the doctor right away.

  • We have a lot of errands to do tomorrow. You ______ wake up late.

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