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Unit 7.1

Must vs Have to

Modal Verbs

Both must and have to belong to the group of auxiliary modal verbs that have no meaning on their own but they modify the main verb, change its meaning and give more details about the action.

Must and have to are used to express certainty, necessity or strong obligation which comes from internal or external factors.

There are some structural differences between must and have to. With must the form is always the same, even for the third person singular.

Affirmative forms:

  • Must: Subject + must + verb + …
  • Have to: Subject + have/has to + verb + …

Negative forms:

  • Must: Subject + must + not + verb + …
  • Have to: Subject + do/does + not+ have to + verb + …

Interrogative forms:

  • Must: Must + subject + verb + …?
  • Have to: Do/does + subject + have to + verb + …?
  • Affirmative
    • I must stop eating sweets (I want to do it).
    • I have to stop eating sweets (my doctor ordered me to stop).
  • Negative
    • You mustn’t read this book (you are not allowed).
    • You don’t have to read this book (you have a choice to read it or not).
  • Interrogative
    • Must you wear the same suit every day (is it necessary for you)?
    • Do you have to wear a suit at work (is it obligatory at your workplace)?

Must is used when we want to show that there are personal circumstances which make the action obligatory, and the speaker has decided that is necessary. Must shows a stronger obligation than have to.

Have to is used when we want to show that somebody else has made something obligatory.

In the negative form there are different uses:

  • Mustn’t usually expresses prohibition;
  • Don’t have to usually expresses that something is not necessary to be done.

Must and have to are two modal verbs which are used to express strong obligation or the need to do something:

  • Must expresses strong obligation which comes from inside. Mustn’t usually expresses prohibition;
  • Have to is generally used to show that there is an obligation imposed by external factors. Don’t have to usually expresses that something is not necessary to be done.

For example:
— “I must start a diet, I do not like my appearance.” / “I have to start a diet, the competition is soon.” = In the first sentence the subject is obliged to start a diet because of personal reasons. In the second sentence the subject is obliged to start a diet because of external reasons.

NOTE: The form of must is always the same, even for the third person singular.

Let’s revise this content within the {Form} section. Take a look at the {Example} section that shows its use within a context.

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