must it is a modal verb (modal verb) which in affirmative sentences can mean have to, to owe, to need and in negative sentences can indicate prohibition.
Examples:
- You must eat healthy food. (You must/need/have to eat healthy food.)
- She must not drink coffee so many times a day. (She shouldn't drink coffee that many times a day.)
As with all modal verbs, must it plays the role of auxiliary verb and, for this reason, it accompanies and influences the meaning of a main verb.
This main verb must be used in the infinitive without the I'm. Note that in the first example, the main verb is to eat, however, it was used without the I'm (eat).
when to use must?
As a general rule, we can say that when must is used in affirmative sentences, indicates the idea of obligation or deduction. In negative sentences, the idea indicated by must it's from prohibition.
- She must stop tuxedo. (She has to stop smoking.) – HAVE/OBLIGATION
- they must help him. (They should help you.) – DUTY/OBLIGATION
- he must be sleeping. (He must be sleeping.) – DUTY/DEDUCTION
- You must be here at 8 am. (You need to be here by 8:00.) – NEED/OBLIGATION
- You must not drink and drive. (You must not drink and drive.) – DUTY/PROHIBITION
How to use must?
The verb must can be used in sentences affirmatives, negative and interrogatives.
Check the table below with the conjugation
| AFFIRMATIVE | NEGATIVE | INTERROGATIVE |
|---|---|---|
| I must study You must study He/she/it must study we must study You must study they must study |
I must not/mustn’t study You must not/mustn’t study He/she/it must not/mustn’t study We must not/mustn’t study You must not/mustn’t study They must not/mustn’t study |
Must I study? Must you study? Must he/she/it study? Must we study? Must you study? Must they study? |
IMPORTANT
- If so, we use the must for all people, including he/she/it. the rule of Simple Present which requires the addition of the –s for third-person inflections is not applied here.
- To form sentences in negative form, we can use must not or the contracted form mustn’t. The meaning of both forms is the same.
- When making sentences with must in the interrogative form, just change the position of this modal verb in the sentence: unlike what happens in the affirmative, in the interrogative the verb must must be positioned before the subject.
Difference between must and have to
In affirmative sentences, both the verb must as for the verbal construction have to (or has to for he/she/it) can be used in the same sense.
Examples:
- she has to wake up early. (She has to get up early.)
- she must wake up early. (She has to get up early.)
- We have to call the director tomorrow. (We have to call the director tomorrow.)
- We must call the director tomorrow. (We have to call the director tomorrow.)
must and have to can be used to reference the gift and to future. However, to refer to the past, we can only use have to.
Like most modal verbs, must it doesn't have a past form.
- she had to wake up early. (She had to get up early.)
- We had to call the director yesterday. (We had to call the director yesterday.)
While in affirmative sentences we can use must or have to without changing the meaning, the same does not happen in negative sentences.
In negative sentences, the meaning will be different depending on the verb used.
Examples:
- Paul must not go. (He shouldn't go.)
- Paul doesn’t have to go. (He doesn't need to go.)
Note that in the first sentence, with must, Paul must not do what is being referred to: go to a certain place. In the second sentence, he doesn't need to go, but if he does, he doesn't have a problem.
In other words, the use of must not indicates practically a categorical order and the use of don’t have to (with I, you, we and they) or I dont have to (with he, she and it) indicates an optional situation.
That said, it follows that the difference between the use of must and have to is related to negative sentences, where each verb gives a certain meaning in the sentence.
In affirmative sentences, the use of one form or another is indifferent and the meaning remains.
Video
Watch the video and see a summary of using must.
Exercises
Fill in the gaps with the correct form.
1. You _____________.
a) must smoke
b) must not smoke
c) have to smoke
d) has to smoke
Correct alternative: b) must not smoke
2. She she _____________ on time.
a) mustn’t arrive
b) must not arrive
c) have to arrive
d) has to arrive
Correct alternative: d) has to arrive
3. We _____________ the bill yesterday.
a) must pay
b) must not pay
c) have to pay
d) had to pay
Correct alternative: d) had to pay
4. Your mom is really tired. You _____________ her with the housework.
a) must help
b) must not help
c) has to help
d) mustn’t help
Correct alternative: a) must help
5. You _____________ junk food everyday.
a) must eat
b) have to eat
c) must not eat
d) has to eat
Correct alternative: c) must not eat
Learn more about English verbs:
- How to use the modal might?
- verb to have
- Verb to be
- English auxiliary verbs
- Phrasal verbs
- simple past
- ought to
- Should