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Must, Have To and Should

Level: A2 · Free grammar guide

H1: Must, Have To and Should

Direct answer

Use must and have to to say that something is necessary or required. Use mustn't to say something is forbidden. Use don't have to to say something is not necessary. Use should to give advice or say what is a good idea — it is weaker than must.

The rule / form box

Must / Have to — obligation and necessity

Mustn't — prohibition (forbidden)

Don't have to — no obligation (not necessary)

Should — advice

Must vs Have to: In British English, there is a tendency to use must for rules you give yourself (personal obligation) and have to for rules from outside (school, work, law). But this is a tendency, not a strict rule — the two overlap a lot. In American English, must is rarely used for obligation; have to is the normal choice. Both must and have to are correct for obligation in any variety.

Must / Mustn't for strong advice: Must and mustn't can also give strong advice or insist: You must try this cake! You mustn't worry. Should is softer.

Past: Must has no past form. For past obligation, use had to: I had to work late yesterday.

Questions: Do I have to...? is the usual question. Must I...? is possible but formal.

Comparison table

MeaningExample
must / have toObligation — it is necessaryYou must stop at a red light.
mustn'tProhibition — it is forbiddenYou mustn't smoke in here.
don't have toNo obligation — it is not necessaryYou don't have to pay — it's free.
shouldAdvice — it is a good ideaYou should drink more water.
shouldn'tAdvice against — it is not a good ideaYou shouldn't eat so late.

The trap: Mustn't and don't have to look similar but mean opposite things. You mustn't go = don't go, it's forbidden. You don't have to go = you can stay home if you want, no problem.

Examples (10)

  1. You must show your passport at the airport. (Rule — required.)
  2. I have to get up at 6 a.m. for work. (Necessity from my job.)
  3. You mustn't park here — it's for ambulances only. (Forbidden.)
  4. You don't have to bring anything to the party. (Not necessary — just come.)
  5. You should wear a jacket. It's cold outside. (Advice.)
  6. You shouldn't leave your bag here. Someone might take it. (Advice against.)
  7. We had to cancel the trip because of the storm. (Past obligation.)
  8. Do I have to fill in this form? (Question about obligation.)
  9. Children must be quiet in the library. (Rule.)
  10. You should try the local food when you visit. (Recommendation.)

    11. Common mistakes

    ❌ You must to wear a helmet.

    ✅ You must wear a helmet. (After must, use the base verb with no to.)

    ❌ You mustn't go to school tomorrow — it's a holiday.

    ✅ You don't have to go to school tomorrow — it's a holiday. (Mustn't = forbidden. Don't have to = not necessary. School is closed, so going is not required — not forbidden.)

    ❌ I musted work late yesterday.

    ✅ I had to work late yesterday. (Must has no past form. Use had to.)

    ❌ You should to study more.

    ✅ You should study more. (After should, use the base verb with no to.)

    ❌ You don't must go.

    ✅ You don't have to go. / You mustn't go. (Don't must does not exist. Choose don't have to = not necessary, or mustn't = forbidden.)

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    Exercises (16)

    Instructions: Choose the correct answer. Each answer shows an explanation.

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    Exercises

    Choose the correct answer. You will see the explanation after checking.

    1. You ___ wear a seatbelt in a car. It's the law.
    2. You ___ smoke in this restaurant. It's forbidden.
    3. You ___ bring food — lunch is provided.
    4. You ___ see a doctor if the pain doesn't stop.
    5. I ___ work late yesterday because the project was urgent.
    6. You ___ park here. This space is for disabled drivers only.
    7. ___ I ___ this form now, or can I do it later?
    8. You ___ tell anyone about this. It's a secret.
    9. It's Saturday. You ___ get up early — there's no school.
    10. Students ___ hand in their homework by Friday.
    11. Choose the correct sentence:
    12. You ___ eat so much sugar. It's bad for your teeth.
    13. We ___ buy tickets in advance — we can buy them at the door.
    14. You ___ be quiet in the library.
    15. I ___ go to work yesterday — it was a public holiday.
    16. You ___ leave your passport at the hotel. Keep it with you.

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