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Master English Grammar

Modal Verbs: Must and Have to for Necessity

Learn how to use the modal verbs must and have to to express necessity and obligation.

What Are Must and Have to?

Must and have to are used to express strong necessity or obligation. They are often interchangeable but have slight differences in usage.

Why Is This Important?

Understanding when to use must and have to correctly helps in giving clear instructions and expressing rules or personal obligations accurately.

Key Points

  • Use must for strong personal obligations
    • I must finish my work before I leave.
    • You must call your mother today.
  • Use have to for external rules and requirements
    • We have to wear a uniform at school.
    • She has to take an exam to pass the course.
  • Use the negative form for lack of necessity
    • You don’t have to come if you don’t want to.
    • He must not touch that—it’s dangerous!

Rules for Using Must and Have to

  • Use must when expressing strong personal obligations or urgent necessity.

    • I must go to the doctor today.
    • You must finish your assignment before the deadline.

  • Use have to for obligations imposed by outside forces.

    • She has to wear a seatbelt while driving.
    • We have to follow the company rules.

  • Use must not to indicate prohibition.

    • You must not enter this restricted area.
    • He must not eat too much sugar.

  • Use don’t have to when something is not necessary.

    • You don’t have to wake up early on Sundays.
    • She doesn’t have to attend the meeting.
ExampleModalUse
I must finish my work before leaving.MustStrong personal obligation
She has to follow the rules at work.Have toExternal obligation
You must not smoke in the building.Must notProhibition
We don’t have to work on Sundays.Don’t have toLack of necessity

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