Explanation
Exercises
Must / Mustn’t vs Have to / Don’t have to — form & use

Quick meaning

  • must speaker’s own view → internal obligation / strong advice.
  • have to rule, timetable, situation → external obligation / necessity.
  • mustn’t = prohibition (it’s not allowed).
  • don’t/doesn’t have to = no necessity (optional). Not the same as mustn’t.

Forms you’ll need

MeaningPresentPastFuture
Obligationmust / have/has tohad towill have to
Negativemustn’t / don’t/doesn’t have todidn’t have towon’t have to
QuestionsDo/Does … have to…? (more common than Must…?)Did … have to…?Will … have to…?

⚠️ must has no past or infinitive forms; use have to instead (e.g., to have to, have had to, having to).

Use must

  • Internal obligation / the speaker’s opinion: You must see the new exhibition.
  • Strong advice: You must drink more water.
  • Negative prohibition: mustn’t You mustn’t park here.

Use have to

  • External obligation (rules, schedules, situations): We have to wear helmets at work.
  • All tenses are possible: I’ve had to work weekends since May.
  • Spoken BrE alternative: have got to → I’ve got to go now.

Don’t mix these up

mustn’t = prohibited

  • You mustn’t use your phone in exams. ✖ not allowed

don’t have to = not necessary

  • You don’t have to wait—I can email you later. ✔ optional

Synonyms: can’t / be not allowed to ≈ mustn’t.

Making negatives & questions

  • Have to uses do/does/did: Do you have to leave now? • She doesn’t have to work tonight. • Did you have to pay?
  • Must negative is mustn’t: You mustn’t be late.
  • Questions with must are possible but less common: Must we fill in this form?

Related verbs

  • should / shouldn’t = advice/opinion, weaker than must/have to.
  • need to = necessity. Negative: don’t/doesn’t need to ≈ don’t have to. BrE modal form: needn’t + base verb (e.g., You needn’t come).

Mini examples

  • Internal obligation: I must call my parents.
  • External rule: Visitors have to wear badges.
  • Future necessity: You will have to renew your visa.
  • Past necessity: We had to cancel the trip.
  • No necessity: You don’t have to print the form.
  • Prohibition: Employees mustn’t share passwords.
Exercises:
1
2
3

Must / Mustn't vs Have to / Don't have to

1
In the library you speak quietly.
2
Employees wear an ID badge at all times.
3
You look pale — you see a doctor.
4
You park here; it’s for ambulances only.
5
It’s going to be sunny, so we take umbrellas.
6
I finish the report by midnight yesterday.
7
Luckily we queue — our names were on the list.
8
If the strike continues, we work from home next week.
9
He leave early today — he has an exam at 8 a.m.
10
You eat so much sugar; it’s bad for your teeth.

Must / Mustn't vs Have to / Don't have to

1
You must wear a helmet here.
A.
B.
C.
2
Students don’t have to buy the textbook.
A.
B.
C.
3
You mustn’t feed the animals.
A.
B.
C.
4
We had to leave early yesterday.
A.
B.
C.
5
Visitors are not allowed to park here.
A.
B.
C.
6
You don’t have to call me back tonight.
A.
B.
C.
7
You should back up your files regularly.
A.
B.
C.
8
Employees must wear ID badges at all times.
A.
B.
C.
9
We must be at the airport by 6 a.m.
A.
B.
C.
10
You shouldn’t eat so much sugar.
A.
B.
C.

Must / Mustn't vs Have to / Don't have to

must mustn't should shouldn't have to don't have to ought to ought not to had to will have to
1
All passengers wear a seat belt while the plane is taxiing.
2
It’s getting chilly; you take a jacket.
3
Employees submit their expenses within five working days.
4
You smoke in the laboratory. It’s dangerous.
5
Visitors make an appointment; reception can register you on arrival.
6
Given the findings of the inquiry, the minister resign.
7
During the investigation, staff comment to the media.
8
My laptop crashed, so I present without slides.
9
If we want the permit, we file the application by Friday.
10
You eat so late at night; it can affect your sleep.