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

Have to, must, should: Obligation, prohibition, necessity, advice

Choose the correct option to complete the sentences below.
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.

Have to, must, should: Obligation, prohibition, necessity, advice

Choose the forms that mean the same as the underlined words.
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.

Have to, must, should: Obligation, prohibition, necessity, advice

Complete the following sentences with the most appropriate modal verb from the list below. Remember that ought to is more formal than should. Use ought to (and NOT should) in the more formal sentences
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.