English Grammar Basic Grammar and syntax

Full use of must in English

Full 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 full uses of the modal must in English. Let’s study all the uses of must.

1. To talk about an obligation/necessity

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


  • You must pass this test to sit in the 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)

NOTA: si estamos hablando de algo que no es una obligación o una necesidad, utilice las siguientes expresiones:

  • 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)

Tenga en cuenta que usar ‘must not‘ para traducir el mismo significado será un error.

2 To give opinions

The modal must be used sometimes 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.

Tenga en cuenta que cuando usamos must para dar opiniones, las opiniones a veces pueden parecer una obligación o una sugerencia fuerte. Para evitar esta confusión, use el modal debería:

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

3. To give recommendation

We often use the must modal to give strong recommendations. We recommend someone to do something because 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.

NOTA: usamos ‘no debería’ para una recomendación negativa.

  • 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 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.

NOTA: si la sugerencia o consejo es negativo, el uso no debe:

  • 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 we are not 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 struck in traffic.

NOTA: si su suposición es negativa. No use must not, use lo siguiente:

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 call anyone at night.

6. MUST change to HAD TO indirect direct

Must in direct speech changes to ‘had to’ in 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)

Usamos must not para prohibir que alguien haga algo.


  • 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.

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