Complete use of MUST in English

Must is a modal auxiliary verb that helps the main verb in a sentence. In this post, we learn the complete usages of the modal must in English. Let’s study all the usages of must.

1. To talk about an obligation/necessity

We use must to talk about an obligation (law, rule, or order). The obligation can be internal too: you are pushing yourself to do something to an extent that it starts feeling like an obligation. We also use must when you understand the importance of doing something and know it is the right thing to do.


  • You must pass this test to sit in interview. (obligation)
  • We must change our game plan. This does not seem to be working. (necessity)
  • We must return his money. He will call the police on us if we don’t. (necessity)
  • You must wear a seat belt while driving. (obligation)
  • You must achieve the targets set for the month, or you will not get the salary. (obligation)
  • We must join his class. I think we will fail the subject if we don’t. (necessity)
  • I must find a new place to live. This is eating all my money. (necessity)

NOTE: if we are talking about something that is not an obligation or a necessity, use the following expressions:

  • Don’t have to or Doesn’t have to
  • Needn’t (need not)


  • You don’t have to pass the test to sit in the interview. (= it is not required or necessary to pass the test in order to sit in the interview)
  • You needn’t vacant the flat. (= it is not required or necessary to vacant the flat)

Note that using ‘must not‘ to render the same meaning will be a mistake.

2. To give opinions

The modal must is sometimes used to give opinions. 


  • We must stand against the bullies. This is the only way to deal with them.
  • The government must close down the unauthorized liquor shops.
  • Students must follow the people who have done something significant in society.
  • I must tell you, you are quite good at this.
  • I must admit that the party was amazing.

Notice that when we use must to give opinions, the opinions sometimes may look like an obligation or a strong suggestion. To avoid this confusion, use the modal should:

  • Students should follow the people who have done something significant in society.
  • The government should close down the unauthorized liquor shops.

3. To give recommendation

We often use the modal must to give strong recommendations. We recommend someone to do something as we want the person to experience what we have already experienced and enjoyed.


  • You must listen to Gary Vee for once. Your life will not be the same after that.
  • You must watch this movie. It is mindblowing.
  • You must try the mix sauce pasta from this place. It is heavenly.
  • You must take your family to this place. It is a beautiful place for a vacation.

NOTE: we use ‘should not’ for a negative recommendation.

  • You should not watch this movie. It is boring. (not recommending to do something)

4. To give suggestions/advice

We use must to give a suggestion or a piece of advice. Using must here makes the suggestion/advice very strong.


  • He must stop hanging out with him. He is into criminal activities.
  • You must take some rest now; you will pass out soon if you keep working.
  • You must take this seriously, or you will lose your job.
  • She must call the police and get them locked up.

NOTE: if the suggestion or advice is negative, use should not:

  • He should not hang out with him. He is into criminal activities.
  • You should not leave this job.

5. To talk about certainty

We use must to talk about something that we think is true but don’t know for sure. Here, we make logical assumptions based on evidence to predict a situation: to deduce or conclude it.


  • He does not usually take a day off. He must be sick.
  • Someone just rang the bell. It must be Rohan.
  • She is not picking up my call. She must be busy.
  • It is Sunday today. The market must be petty crowded.
  • The ground looks wet. It must have rained last night.
  • Aaru did not call me last night. She must have been mad at me.
  • He was late to work. He must have gotten stuck in traffic.

NOTE: if your assumption is negative. Don’t use must not, use the following:

Jon: Someone just rang the bell. It must be Simi.
Ashish: No, it can’t be Simi. She has gone shopping.

Aarushi: I was getting a call from an unknown number last night. It must be Mangesh.
Ashish: It couldn’t be Mangesh. He does not call anyone at night.

6. MUST changes to HAD TO in indirect speech

Must in the direct speech changes to ‘had to’ in the indirect speech.


  • Direct speech: He said, “You must complete the task before Sunday.”
  • Indirect speech: He said that I had to complete the task before Sunday.
  • Direct speech: Jon told me, “I must take this offer.”
  • Indirect speech: Jon told me that he had to take this offer.

7. To forbid something (must not)

We use must not to forbid someone from doing something.


  • You must not park your car here. 
  • You must not play music after 10 pm.
  • You must not consume liquor while driving.
  • Students must not use phones in the examination.
Complete uses of MUST in English
Complete uses of MUST in English

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Ashish found his first love—the English language—a few years back. Since then, he has been immersed in the language, breaking down the language and teaching it to passionate English learners. He has a flair for listening to the English language (podcasts, sitcoms, stories), observing the nuances, and making it easy for English learners. He is known for breaking down complex English topics and making them easy to be understood.

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