Must and have to
How to use must and have to for obligation, why must not and do not have to mean opposite things, and how have to changes with tense.
When you use it
Must and have to both say that something is necessary. Must usually comes from the speaker: a rule you set, a strong personal feeling, something you tell yourself. Have to usually comes from outside: a law, a timetable, an employer, a situation. In everyday conversation have to is the more common of the two, and in the past and the future only have to can be used. The negatives are the important part: must not forbids, do not have to says there is no need.
How it is formed
Must is a modal: one form for all subjects, base verb after it, no do in questions and negatives. Have to behaves like an ordinary verb: it changes with the subject and takes do for questions and negatives.
| must | have to | |
|---|---|---|
| Affirmative | I / she must wear a helmet | I have to wear a helmet; she has to wear a helmet |
| Negative | I must not wear it (it is forbidden) | I do not have to wear it (it is not necessary) |
| Question | Must I wear it? (rare) | Do I have to wear it? Does she have to wear it? |
| Past | (no past form) | I had to wear it |
| Future | (no future form) | I will have to wear it |
Short forms: mustn't, don't have to, doesn't have to, didn't have to. British English also uses have got to in speech: I've got to go. It has the same meaning as have to but only a present form.
| Meaning | Form | Example |
|---|---|---|
| Necessary, speaker's own authority | must | You must be home by ten. |
| Necessary, outside authority | have to | I have to show my passport at the border. |
| Forbidden | must not | You must not smoke here. |
| Not necessary | do not have to | You do not have to pay; it is free. |
| Necessary in the past | had to | We had to wait an hour. |
In signs and written rules must is the normal choice; in conversation about your own life have to sounds more natural. The two often overlap, and choosing the wrong one is rarely a real error. Choosing the wrong negative is.
Examples
- You must wear a seatbelt in the car.
- I have to finish this report by Friday; my manager is waiting for it.
- Anna has to work on Saturdays this month.
- You must not forget your keys again.
- Tom does not have to get up early tomorrow; it is a holiday.
- We had to pay for the tickets in cash.
- Do you have to be at the office at eight?
- I must call my mother tonight; I promised.
Common mistakes
- ✗ You mustn't pay; it is free.
✓ You don't have to pay; it is free.
This is the mistake that changes the meaning. Both Ukrainian «не повинен» and Russian «не должен» can mean "forbidden" or "not required" depending on context. English splits them: must not means prohibited, do not have to means optional. - ✗ She must to go now. / ✗ She musts go now.
✓ She must go now.
Must is a modal: no to after it and no ending on it. The verb that follows is always the base form. - ✗ Yesterday I must work late.
✓ Yesterday I had to work late.
Must has no past. In Russian «должен был» simply adds «был»; English switches to have to and puts that verb in the past. - ✗ Do you must work on Sundays? / ✗ Must you to work?
✓ Do you have to work on Sundays? / Must you work on Sundays?
Do goes with have to, never with must. The question with must is grammatical but sounds formal; most speakers ask with have to. - ✗ She have to study. / ✗ He don't have to come.
✓ She has to study. / He doesn't have to come.
Because have to is an ordinary verb, it needs -s with he, she, it and does in the negative. Learners who treat it like a modal forget the agreement.
Try it
- You ___ (not) talk during the exam. It is against the rules.
- Tom ___ (not) cook tonight; Anna has already made dinner.
- Last year I ___ take the bus every day because my car was broken.
- ___ Anna ___ wear a uniform at work?
- I ___ remember to buy milk; there is none left. (my own decision)