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Must & Have To

Express obligation, necessity, and strong recommendations

What are Must and Have To?

"Must" and "have to" both express obligation and necessity, but they have subtle differences. "Must" often expresses personal conviction or internal obligation, while "have to" typically expresses external rules or requirements.

Compare: "I must study harder" (personal decision) vs. "I have to wear a uniform" (external rule).

When to Use MUST

Strong Internal Obligation (Personal Conviction)

Examples

  • I must stop smoking. (I feel this strongly)
  • We must finish this today. (personal commitment)
  • You must see this movie - it's amazing! (strong recommendation)
  • I must call my mother tonight.
  • She must study harder if she wants to pass.

Rules and Laws (Formal/Written)

Examples

  • All passengers must wear seat belts. (official rule)
  • You must be 18 to vote. (legal requirement)
  • Students must submit assignments by Friday.
  • Visitors must sign in at reception.
  • You must not smoke in the building. (prohibition)

Logical Deduction (Must Be True)

Examples

  • She's been studying all day. She must be tired. (logical conclusion)
  • You've been working for 10 hours. You must be hungry.
  • It's 10 PM and the lights are off. They must be sleeping.
  • He speaks perfect French. He must have lived in France.
  • The ground is wet. It must have rained.

When to Use HAVE TO

External Obligation (Rules, Requirements, Circumstances)

Examples

  • I have to wear a uniform at work. (company rule)
  • You have to show your passport at the border. (legal requirement)
  • She has to take medicine every day. (medical necessity)
  • We have to pay rent by the 1st of the month.
  • Children have to go to school.
  • I have to wake up early tomorrow. (circumstance)

Past Obligation (Only 'Had To,' NOT 'Must')

Examples

  • Yesterday I had to work late. (past obligation)
  • She had to cancel her trip.
  • We had to wait for two hours.
  • They had to call the police.

Questions About Obligation (Only 'Have To,' NOT 'Must')

Examples

  • Do I have to come to the meeting?
  • Does she have to work on weekends?
  • What time do we have to be there?
  • Did you have to pay?

Future Obligation (Both Work, but 'Have To' Is More Common)

Examples

  • I will have to study tonight.
  • She will have to find a new job.
  • We 'll have to leave early tomorrow.

Formation

MUST - Positive

Subject + must + base verb

Examples

  • I must go now.
  • You must try this.
  • She must study harder.
  • We must finish today.

MUST - Negative

Subject + must not (mustn't) + base verb

Examples

  • You must not smoke here. (prohibition - it's forbidden)
  • We mustn't be late.
  • Students must not cheat on exams.

HAVE TO - Positive

Subject + have/has to + base verb

Examples

  • I have to go to the doctor.
  • She has to work tomorrow.
  • We have to pay taxes.

HAVE TO - Negative

Subject + don't/doesn't have to + base verb

Examples

  • You don't have to come if you don't want to. (no obligation - it's optional)
  • She doesn't have to work on Sundays.
  • We don't have to hurry.

Common Mistakes

Common Mistakes

  • ❌ I must to go. → ✅ I must go. (no "to" after must)
  • ❌ You mustn't come. → ✅ You don't have to come. (mustn't = prohibited, don't have to = not necessary)
  • ❌ Must I go? → ✅ Do I have to go? (use "have to" for questions)
  • ❌ Yesterday I must work. → ✅ Yesterday I had to work. (use "had to" for past)
  • ❌ She musts study. → ✅ She must study. (no -s on modals)
  • ❌ I have to went. → ✅ I have to go. (base form after "have to")
  • ❌ You don't must smoke. → ✅ You must not smoke. (use "must not," not "don't must")
  • ❌ I must went yesterday. → ✅ I had to go yesterday.

Practice Tips

Practice Tips

  • ⚠️ Mustn't vs. Don't have to: "Mustn't" = prohibited (forbidden). "Don't have to" = not necessary (optional). VERY different meanings!
  • ⏱️ Time limitations: "Must" has no past form. Use "had to" for past: "I had to leave early yesterday."
  • ❓ Questions: Use "Do you have to...?" NOT "Must you...?" for natural English.
  • 💡 Strong advice: Use "must" for strong recommendations: "You must watch this show!"
  • 🔍 Deduction: Use "must" for logical conclusions: "She must be happy" (based on evidence).

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