Must vs Have to

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 action.

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

Below we can see structural differences between Must and Have To.

Affirmative

  • Must: Subject + must* + action;
  • Have to: Subject + have to + action (“has” for the third person).

Negative

  • Must: Subject + must* + not + action;
  • Have to: Subject + do + not+ have to + action (“does” for the third person).

Interrogative

  • Must: Must*subject + action + (?);
  • Have to: Do + subject + have to + action + (?) (“does” for the third person).

*The form is always the same, even for the third person.

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 choice: you can but it is not obligatory.)

Interrogative

  • Must you wear the same T-shirt 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 makes it 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 it obligatory (it is the external circumstances that make it so).

Negative form meaning differences:

  • 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 HAVE TO
A. Subject + must* + action. Subject + have to + action (“has” for the third person).
N. Subject + must*  + not + action. Subject + do + not+ have to + action (“does” for the third person).
I. Must*subject + action + (?). Do + subject + have to + action + (?) (“does” for the third person).

*The form is always the same, even for the third person.

They differ in meaning:

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

For example:
— “I must start a diet.” = The subject is obliged to start a diet because of  personal reasons.
— “I have to write an essay for mythology class.” = The subject is obligated to write an essay for mythology class (Mythology class = external factor).

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