Must vs. Have to | Must Not vs. Don’t Have to

Last updated on August 1, 2024 by Grammargeek

Understanding the nuances of English modal verbs can be tricky, especially when it comes to “must” and “have to.” Both expressions convey the idea of obligation or necessity but are not always interchangeable. This reference will cover the definitions, general usage, and helpful tips for the correct use of these terms.

By reading this reference, you will gain a clear understanding of when to use “must” or “have to” accurately in your writing and speech.

Must vs. Have to: Understanding the Basics

Must vs. Have to, Must Not vs. Don't Have to
Must vs. Have to, Must Not vs. Don’t Have to – Created by 7ESL

Definition of Must and Have to

When talking about obligations in English, “must” and “have to” are often used. These expressions describe duties, responsibilities, or necessities.

  • Must: Used when talking about a requirement or necessity that comes from the speaker or writer. It is a modal verb, showing personal determination or obligation.
  • Have to: Used when the obligation comes from an external source, such as laws, rules, or someone else’s decision. It is formed by the auxiliary verb “have” plus the infinitive “to.”

General Usage of Must and Have To

You use must to express a strong obligation usually coming from yourself. For example:

  • We must remember to lock the doors before leaving.
  • You must follow the instructions carefully.

Have to is often used for obligations imposed by external circumstances, such as rules, laws, or situations beyond personal control:

  • We have to pay our taxes by April 15th.
  • She has to attend the meeting because it’s mandatory.

Helpful Tips for Correct Use

When deciding between must and have to, consider the source of the obligation.

  • Use “must” for personal obligations or strong recommendations:
    • We must remember to water the plants.
  • Use “have to” for obligations from external authorities, like laws or rules:
    • We have to wear a helmet when riding a bike.

Examples

Examples of “Must”

  • You must wear a helmet when riding a motorcycle for your safety.
  • She must complete her assignment before she can go out with her friends.
  • We must conserve water during the drought.
  • He must apologize for his behavior before the situation escalates.
  • Students must attend the lecture to understand the material.

Examples of “Have to”

  • I have to wake up early tomorrow to catch my flight.
  • They have to finish the project by the end of the week to meet the deadline.
  • You have to take your shoes off before entering the house.
  • She has to take medication every four hours for her condition.
  • We have to be at the theater by 7 PM if we want to see the show.

Practice and Application

Fill-in-the-Blank 

  1. You _____ wear a helmet when riding a motorcycle. (must/have to)
  2. I _____ finish my homework before I can go out tonight. (must/have to)
  3. She _____ attend the meeting; it’s mandatory. (must/have to)
  4. They _____ get their car repaired; it’s making a strange noise. (must/have to)
  5. We _____ obey the rules while we are in school. (must/have to)
  6. He _____ see a doctor if his symptoms continue. (must/have to)
  7. Passengers _____ check in at least two hours before the flight. (must/have to)
  8. You _____ be kidding me! That can’t be true. (must/have to)
  9. We _____ take care of the environment for future generations. (must/have to)
  10. She _____ be at the office by 9 AM for the conference call. (must/have to)

Answers

  1. You must wear a helmet when riding a motorcycle.
  2. I have to finish my homework before I can go out tonight.
  3. She must attend the meeting; it’s mandatory.
  4. They have to get their car repaired; it’s making a strange noise.
  5. We must obey the rules while we are in school.
  6. He has to see a doctor if his symptoms continue.
  7. Passengers must check in at least two hours before the flight.
  8. You must be kidding me! That can’t be true.
  9. We must take care of the environment for future generations.
  10. She has to be at the office by 9 AM for the conference call.

Frequently Asked Questions

What is the main difference between “must” and “have to”?

  • Must imply a personal obligation.
  • Have to suggest an external requirement.

Can “must” and “have to” be used interchangeably?
Generally, yes, in the present tense when expressing obligation. But “must” often conveys stronger necessity.

Do “must” and “have to” change in the past tense?

  • Must does not change.
  • Have to change to “had to”.

Examples of “must” and “have to” in use:

  • You must stop at the red light. (personal feeling of obligation)
  • You have to stop at the red light. (legal requirement)

Does “must” make a statement sound more formal?
Yes, “must” can sound more formal or emphatic.

Can “must” be used for deductions?
Yes, you can use “must” for deductions or assumptions.
E.g., She must be the manager because she’s giving orders.

Verb Usage Example
Must Personal obligation We must eat healthier.
Have To External obligation We have to pay taxes.
Must Deductions/assumptions They must be away.
Have To General obligation, past tense Yesterday, we had to leave early.

Is “must” used in questions about obligation?
Rarely. “Do you have to…?” is more common than “Must you…?” in questions.

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