The Uses of "Must" in English

The modal verb must is commonly used in English to express obligation, necessity, certainty, prohibition, or strong recommendations. It is a versatile word that conveys a sense of importance or certainty in a variety of contexts. In this article, we’ll explore the uses of must, its negative form, and provide examples and exercises.

1. To Express Obligation or Necessity

Must is often used to indicate that something is required or necessary. It conveys a strong sense of obligation.

Examples:

• You must wear a seatbelt while driving.

• Employees must arrive at work on time.

• We must finish this project before the deadline.

2. To Show Strong Certainty

Must is used to express that the speaker is sure about something based on evidence or reasoning.

Examples:

• She must be at home; the lights are on.

• You’ve been working all day—you must be tired.

• It must be cold outside; everyone is wearing coats.

3. To Give Strong Recommendations

Must can be used to emphasize that something is highly recommended or important.

Examples:

• You must try this dessert—it’s delicious!

• Visitors must see the Eiffel Tower when in Paris.

• You must read this book; it’s a masterpiece.

4. To Express Prohibition (in the Negative Form)

The negative form, must not or mustn’t, is used to express prohibition or to indicate that something is not allowed.

Examples:

• You mustn’t smoke in this area; it’s a non-smoking zone.

• Students must not use their phones during the exam.

• You mustn’t touch that—it’s dangerous!

5. To Express Rules or Formal Requirements

Must is commonly used in official documents, instructions, or formal guidelines to state rules or requirements.

Examples:

• Passengers must show their tickets before boarding the train.

• Applications must be submitted by the deadline.

• All visitors must sign in at the reception desk.

6. To Make Assumptions

Must can also be used when making logical assumptions about something that is likely to be true.

Examples:

• He left an hour ago, so he must be there by now.

• If she’s not answering, she must be busy.

• This must be the right place; the sign matches the address.

Grammar Notes

1. Must is always followed by the base form of the verb:

   • Correct: You must take your passport.

   • Incorrect: You must to take your passport.

2. Must is used with all subjects without any changes:

   • I must, you must, he/she/it must, we must, they must.

3. The negative form is must not or mustn’t, which expresses prohibition:

   • You must not park here.

4. For expressing past obligations, must is replaced by had to:

   • Present: You must attend the meeting.

   • Past: You had to attend the meeting.

Common Expressions with "Must"

• Must I...? (To ask about obligation or necessity)

  • Must I finish this today?

• You must be joking! (Used to express disbelief or surprise)

  • You must be joking if you think I’ll do that!

• Must-see (Something highly recommended to experience or visit)

  • This movie is a must-see!

Exercises

Exercise 1: Fill in the blanks with "must" or "must not."

1. You ________ bring your ID to enter the building.

2. Visitors ________ feed the animals in the zoo.

3. We ________ finish this work by tomorrow.

4. You ________ touch the paintings in the museum—it’s not allowed!

5. Everyone ________ be careful when crossing the street.

Exercise 2: Rewrite the sentences using "must."

1. It is necessary for you to drink plenty of water.

2. It’s against the rules to park here.

3. I am certain she is at home because her car is in the driveway.

4. It’s strongly recommended to visit the Grand Canyon.

5. It is a rule that employees wear their ID badges.

Exercise 3: Identify the use of "must" in each sentence.

1. You must complete your homework before watching TV.
   a) Obligation
   b) Certainty
   c) Prohibition

2. You mustn’t enter this room—it’s restricted.
   a) Obligation
   b) Prohibition
   c) Recommendation

3. She must be happy; she just got promoted.
   a) Certainty
   b) Obligation
   c) Rule