Difference between must and have to

Must and have to- are two frequently used modal verbs in the English language that are used when talking about future obligations or intentions. Both verbs have similar applications, especially when it comes to the first person where, in its practical sense, they have the same meaning.

However, there are structural differences between these two verbs, which we will point out in this article after the definition and description of each of them.


Must is a modal verb that is used in the present and future tense, to express an obligation and/or a prohibition. Therefore, when this verb is used, the sender imposes an obligation. It can also be used to express advice or persuasion emphatically.

In its negative form, it implies that something should not be done and is expressed with the contraction mustn´t (must + not). In its interrogative form, the formula to express a question with the modal verb must is: Must + subject + main verb.

In addition to these applications, the verb must is used to express a moral duty, a strong need, or an affirmative deduction.


  • You run up very fast. You must be tired (You ran very fast. You must be tired) – in this case it expresses an affirmative deduction.
  • You must respect your teachers (you must respect your teachers) – in this case it expresses a moral duty.
  • You mustn’t smoke because you´re very sick – in this case it is a negative sentence.

Have to

Have to is a semi-modal verb (verbs that share some particularities with ordinary verbs and with modal verbs) that is used in the past, present and future tense to express an obligation that is not imposed but transmitted by the sender.

This is formed with have to + the verb in the infinitive. Also, the correct formula for interrogative sentences of this verb is: Do + subject + have to + main verb.

On the other hand, in its negative form, it expresses that it is not necessary to do something and is represented with -Don’t have to-. This verb is also used to express necessity, in which case they are used in other tenses apart from the present, in which the verb must is used.


  • You don’t have to go to that meeting (it is not necessary that you go to that meeting) – negative sentence.
  • I have to do my homework (I have to do my homework) – affirmative sentence of previously imposed obligation.
  • I have to go to the bathroom (I have to go to the bathroom): express need.

Once the applications and uses of these verbs have been described, we find that the most important differences between them are:

Must have-to
It is a modal verb (verbs that are used to express different functions such as obligation, ability, necessity, deduction or prohibition). It is a semi-modal verb (verbs that share some particularities with ordinary verbs and with modal verbs).
It expresses an obligation imposed by the speaker. It conveys an obligation that already exists.
Work with present and future verb tenses. Work with past, present and future verb tenses.

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