Have to, don’t have to, must, mustn’t

Grammar / A2 Grammar lessons and exercises / Have to, don’t have to, must, mustn’t

✏️ Exercises

Must / Mustn’t, Have to / Don’t Have to: Form & Use

Grammar comparison chart highlighting the differences between 'must' and 'have to' in affirmative, negative, and question forms, with correct and incorrect usage examples for A2 English grammar.

📝 Must / Mustn’t — Form

Use must + infinitive without to

Must is a modal verb. Modal verbs are followed by the base form of the verb (infinitive without “to”).

  • ✘ Incorrect: I must to go to the doctor.
  • ✔ Correct: I must go to the doctor.

No -s after he/she/it

Modal verbs do not add -s in the third person singular.

  • ✘ Incorrect: He must comes with us.
  • ✔ Correct: He must come with us.

Use must/mustn’t in negatives and questions

Must is an auxiliary verb. Do NOT use “do/did” in questions or negatives.

  • ✘ Incorrect: We don’t must arrive early.
  • ✔ Correct: We mustn’t arrive early.
  • ✘ Incorrect: Do we must arrive early?
  • ✔ Correct: Must we arrive early?

Past and future forms

Must has no past or future form. Use “had to” or “will have to” instead.

  • ✘ Incorrect: Yesterday, I must take a taxi.
  • ✔ Correct: Yesterday, I had to take a taxi.
  • ✘ Incorrect: You will must take a taxi if it rains tomorrow.
  • ✔ Correct: You will have to take a taxi if it rains tomorrow.

📝 Have to / Don’t have to — Form

Use do and did in negatives and questions

The verb “have” in “have to” is not a modal verb. Use auxiliary verbs (“do,” “does,” “did”) for questions and negatives.

  • ✘ Incorrect: Have you to get up early tomorrow?
  • ✔ Correct: Do you have to get up early tomorrow?
  • ✔ Correct: Did you have to buy a new sound card?
  • ✔ Correct: We don’t have to stay until the end.

No contraction with ‘ve

“Have to” cannot be contracted to “’ve to.”

  • ✘ Incorrect: I ’ve to study for the exam tomorrow.
  • ✔ Correct: I have to study for the exam tomorrow.

Past and future forms

“Have to” works in all tenses — unlike “must.”

  • Past: She had to leave early.
  • Future: They will have to wait outside.

💬 Must vs Have to — Use: Obligation

Have to — Rules and obligations

We use “have to” to talk about rules and obligations — something that is necessary because of external factors.

  • I have to get to work before 7 tomorrow.
  • The car broke down and we had to call a taxi.

Must — Rules and obligations

“Must” is very similar to “have to.” We use “must + infinitive” to talk about rules and obligations.

  • I must go to the doctor.
  • I must get up early tomorrow.

Must — Obligation from the speaker

We normally use “must” when the obligation comes from the speaker’s opinion — they think it’s necessary.

  • Manager: “You must get up early tomorrow. The meeting is at nine.”
    → The manager thinks it’s necessary.
  • Doctor: “You must stop smoking.”
    → The doctor’s advice/opinion.
  • Smoker: “I must stop smoking.”
    → The smoker believes it’s necessary.

Have to — External obligation

We use “have to” when the obligation comes from outside the speaker — rules, laws, or other people.

  • Worker: “We have to get up early tomorrow. The meeting is at nine.”
    → The boss made the rule — not the worker’s own idea.
  • Smoker: “I have to stop smoking.”
    → Because the doctor said so (external requirement).

⚠️ Mustn’t vs Don’t have to — Use: Prohibition vs Lack of Necessity

Don’t have to — Not necessary

“Don’t have to” means there is no obligation. You can do it, but you don’t need to.

  • You don’t have to pick me up at the station. I can take a taxi.
    → It’s optional.
  • You don’t have to wait here.
    → You can wait, but it’s not required.

Mustn’t — Prohibition

“Mustn’t” means it is forbidden. You are not allowed to do it. It’s necessary that you don’t do it.

  • You mustn’t call me before 8.
    → You are not allowed to call before 8.
  • I mustn’t lose my concentration now.
    → It’s dangerous — I’m not allowed to lose focus.
  • You mustn’t wait here.
    → It’s against the rules — you cannot wait here.

🔁 Remember: Mustn’t ≠ Don’t have to
→ Mustn’t = “You are forbidden.”
→ Don’t have to = “It’s okay if you don’t.”

💡 Quick Summary

  • Must = strong obligation (speaker’s opinion), no past/future, no -s, no do/did
  • Have to = external obligation, works in all tenses, uses do/did, no contractions
  • Mustn’t = prohibition — you are not allowed
  • Don’t have to = no obligation — you don’t need to
  • Mustn’t and don’t have to have opposite meanings