Have To and Must: Form, Uses and Differences
Have to and must both talk about obligation, but they are not always the same. The biggest trap is the negative: mustn't and don't have to have very different meanings.
By LearnLingo Team · Updated
Form
| Subject | Affirmative | Negative | Question |
|---|---|---|---|
| I, you, we, they | I must go. | I mustn't go. | Must I go? |
| He, she, it | She must go. | She mustn't go. | Must she go? |
Must is a modal verb: it never changes (no -s), and it is followed by the base verb without to. Questions with must are rare and sound formal; most people ask Do I have to...? instead.
| Subject | Affirmative | Negative | Question |
|---|---|---|---|
| I, you, we, they | I have to go. | I don't have to go. | Do I have to go? |
| He, she, it | She has to go. | She doesn't have to go. | Does she have to go? |
| Past (all subjects) | They had to go. | They didn't have to go. | Did they have to go? |
| Future (all subjects) | We'll have to go. | We won't have to go. | Will we have to go? |
Have to works like a normal verb: it changes for he, she and it, and it uses do, does and did in negatives and questions. In British English you will also hear have got to: I've got to go.
| Form | Meaning | Example |
|---|---|---|
| must, have to | It is necessary. | You must show your passport. You have to show your passport. |
| mustn't | It is not allowed. Don't do it. | You mustn't smoke in here. |
| don't have to | It is not necessary. You can choose. | You don't have to come, but you can if you want. |
Must and have to for obligation
Both must and have to say that something is necessary. In many sentences you can use either one and the meaning is almost the same: I must finish this today and I have to finish this today.
They are built differently. Must is a modal verb, like can and should: it has the same form for every subject and is followed by the base verb without to. Have to is a normal verb: she has to, he doesn't have to, do you have to?
I must remember to buy milk.
She has to get up at five for work.
We have to be at the airport two hours early.
You must be over 18 to enter.
A written rule on a sign or form.
The difference in feeling
In British English especially, there is a small difference in who decides. Must often shows the speaker's own opinion or decision: I feel it is necessary. Have to shows an obligation from outside: a rule, a law, a boss or a timetable.
Compare: I must stop eating so much chocolate (my own decision) and I have to wear a tie at work (my company's rule). Must is also common in written rules and notices: Passengers must wear seat belts.
In American English, have to is much more common in speech, and must can sound very strong or formal. If you are not sure, have to is the safe choice in conversation.
I really must call my grandmother this week.
Nurses have to work at night sometimes.
You must try this cake. It's amazing!
Must for a strong recommendation.
Visitors must sign in at reception.
Mustn't and don't have to
This is the most important part of the topic. In the positive, must and have to are similar. In the negative, they are completely different.
Mustn't (must not) means it is not allowed or it is a bad idea: Don't do it! Don't have to means it is not necessary: you can do it if you want, but you are free to choose.
You mustn't use your phone in the exam (it is forbidden). You don't have to stay until the end of the exam (you can leave early if you finish). Mustn't is mainly British; in American English people usually say can't or shouldn't, or use the full form must not.
You mustn't touch that wire. It's dangerous.
You don't have to bring anything. We have plenty of food.
He doesn't have to work on Saturdays.
We mustn't be late for the interview.
You can't park here.
In American English, can't is the usual way to say something is not allowed.
Past and future forms
Must has no past or future form. For the past, use had to: Yesterday I had to work late. Do not say I musted.
For the future, use will have to: Next year you'll have to pay for the course. For a future obligation that is already arranged, must and have to in the present can also work: I have to see the dentist tomorrow.
Also be careful with must have + past participle: it is not an obligation in the past. It means you are almost sure something happened: She must have missed the bus. That is a different use, explained in modals of deduction.
When I was a child, I had to walk to school.
Did you have to wait long at the doctor's?
We didn't have to pay. It was free.
You'll have to speak to the manager about that.
Have to, must and should
Have to and must are strong: something is necessary. Should is weaker: it is a good idea, a piece of advice. You have to show your ticket (a rule). You should arrive early to get a good seat (advice). Read more in should and ought to.
For commands, we often use imperatives instead: Show your ticket, please. And to ask for permission, use can: Can I go now? See can and could for more.
You have to have a visa to work here, and you should apply early.
You should see a doctor about that cough.
Children must be with an adult in the pool.
In real life
In everyday speech, have to is far more common than must. People also say have got to in British English, and gotta in very informal American English (I gotta go). Do not write gotta in formal texts.
The sound changes in fast speech: have to often sounds like hafta, and has to like hasta. Must is common in friendly recommendations: You must come and visit us! It sounds warm, not like an order.
Sorry, I have to go. My bus is coming.
I've got to finish this report by five.
Very common in British English and also used in American speech; it means the same as have to.
Do we have to dress up for the party?
You must come for dinner some time!
Common mistakes
You don't have to smoke here. It's a hospital.
You mustn't smoke here. It's a hospital.
Don't have to means it is not necessary. To say something is not allowed, use mustn't or can't.
She must to work tomorrow.
She must work tomorrow.
Must is a modal verb, so it is followed by the base verb without to. Have to has to, but must does not.
He have to wear glasses.
He has to wear glasses.
Have to is a normal verb, so it takes -s for he, she and it: has to.
I musted leave early yesterday.
I had to leave early yesterday.
Must has no past form. Use had to for obligation in the past.
Do you must wear a uniform?
Do you have to wear a uniform?
Must does not use do in questions. Ask with Do you have to...? or, more formally, Must you...?
Practice quiz
10 questions. Pick an answer to see if it is right and why.
1. You ___ use your phone during the exam. It's against the rules.
2. Tomorrow is a holiday, so I ___ get up early.
3. My sister ___ wear a uniform at work.
4. Choose the correct sentence about the past.
5. What does You don't have to pay mean?
6. ___ you have to show your ID at the door?
7. Which sentence shows the speaker's own decision?
8. Next year, students ___ pay for parking.
9. Choose the correct sentence.
10. You ___ try the fish here. It's the best in town!
0 of 10 answered
Show all answers
- mustn't
- don't have to
- has to
- Last week I had to work late.
- Paying is not necessary.
- Do
- I must stop drinking so much coffee.
- will have to
- He doesn't have to come.
- must
See what the A2 English course covers, or test your level first.
People also ask
What is the difference between must and have to?+
In the positive they are very similar. Must often shows the speaker's own feeling or a written rule, and have to shows an obligation from outside, like a law or a job. In the negative they are different: mustn't means not allowed and don't have to means not necessary.
Is must more formal than have to?+
Often, yes. Must is common in written rules and notices, and in American English it can sound strong in conversation. Have to is the everyday choice in both British and American speech.
What is the past tense of must?+
Must has no past form for obligation, so we use had to: I had to work yesterday. Must have + past participle (She must have left) is not an obligation; it means you are almost sure something happened.
What does have got to mean?+
Have got to means the same as have to. It is common in informal British English: I've got to go now. It is used mainly in the present, not for the past.
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