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“must” is used with another verb in its infinitive form. “must” does not change for either person or count.

Pattern:

I / you / he, she, it / we / they “must” + V (inf. form)

The negative “not” comes between “must” and its verb:

“must not” + V (inf. form)

“must” is used in two different ways:

1 – to indicate something that we believe to be true
2 – to indicate that doing something is an obligation or necessity

1 – must: belief that something is true

In this sense, it is very similar to “probably”:

John dislikes driving, so I think he must take the train to work. (I think he probably takes the train to work, since he dislikes driving.)

You haven’t eaten all day? You must be hungry! (You are probably hungry!)

I called the Petersons, but no one answered. They must not be home. (They are probably not home.)

There are several newspapers on the neighbor’s driveway. They must be on vacation. (They are probably on vacation.)

2 – must: something is an obligation or necessity

You must be quiet in the library.

All drivers must stop at a red light.

If you want dessert, you must finish your dinner.

It’s quiet hours now in the dormitory. You must not play loud music.

Note: “must not” can be contracted: “mustn’t”

You mustn’t play loud music.

Note: We can also use “have to” in the positive sentences above:

You have to be quiet in the library.

All drivers have to stop at a red light.

If you want dessert, you have to finish your dinner.

For the negative, use “should not”:

It’s quiet hours now in the dormitory. You should not play loud music.

If we need the past tense, we use “had to” and not “must”:

You had to be quiet in the library.

All drivers had to stop at a red light.

If you wanted dessert, you had to finish your dinner.

Exercises:  Complete the sentences. Use “must be” and one of the following verbs.

Example:

Your sister had a new baby? Congratulations! You must be (hungry, happy, tired)!  ==> You must be happy!

1. Jack worked all night. He must be (hungry, happy, tired).
2. It must be (cold, raining, windy). I see everyone is using an umbrella.
3. Class is canceled today. Mrs. Smith must be (sick, hungry, short).
4. John just sits on the couch and sighs. He must be (busy, hot, bored).
5. Mary gets straight As every semester. She must be (dumb, very smart, tall).

Exercises:  Complete the sentences. Use “must” and one of the following verbs.

Example:

Everything in Susie’s room is pink She must (hate, like, know) the color pink.  ==> She must like the color pink.

1. Miss Brown teaches two kindergarten classes every day. She must (know, have, like) the patience of Job.
2. Tom studied for six hours last night. He must (know, write, see) all the material well enough for the test by now.
3. The Jones have a large vegetable garden. They must (drink, wash, eat) plenty of fresh vegetables in the summer.
4. Jane used to have long hair, but now it’s short. She must (have, be, seem) gotten a haircut.
5. Jack seems to know so much. He must (write, read, talk) a lot.

Exercises:  Complete the sentences. Use “must” and one of the following verbs.

Example:

You are going to Disneyworld for your vacation? You must (take, give, bring) a lot of pictures.  ==> You must take a lot of pictures.

1. Hospital visiting hours are over. You must (go, leave, stay) home now.
2. All passengers must (eat, have, read) their passports ready when going through Customs.
3. In most states, you must (have, be, am) 21 to drink alcohol.
4. You must (close, look, sign) this form before submitting it to the office.
5. You must (do, listen, work) your homework if you want to pass the test.

Exercises:  Complete the sentences. Use “must” or “must not”.

Example:

Jack never goes out after work. He (must / must not) like socializing.  ==> He must not like socializing.

1. Matt rides a bike every day, even in the winter. He (must / must not) have a car.
2. Jane has the flu. She (must / must not) feel very well.
3. Tom works at the zoo. He (must / must not) like animals.
4. Grandpa needs a magnifying glass to read the paper. He (must / must not) see very well.
5. Mary’s pie has won a blue ribbon at the county fair. She (must / must not) be a good cook.

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