What’s a Must When Teaching “Must” and “Have To”?

At the request of a fellow teacher, I’m going to review and expand on a posting I shared about one year ago titled Teaching Modal Verbs: Function, Strength, and Formality. This time around, I’d like to focus specifically on must and the modal-like expression have to.

Points to cover when teaching must and have to:


  • They are equal in degree in the affirmative. They can express a high degree of necessity or certainty (close but not quite 100%). 

You must/ have to pay before you pump gas into your car.

You must/ have to be crazy!


  • Have to in the negative loses its strength and expresses the idea of choice, in other words, an action is not necessary but rather optional. 

You have to pay before you pump gas into your car. = It’s necessary to pay before you pump gas into your car.

You don’t have to pay before you pump gas into your car. = It doesn’t matter if you pay before or after.

  • When expressing necessity in the present, have to is preferred in informal (spoken) English and must is generally used in formal speech.  


  • When expressing necessity in the past, only have to is possible. Must have (+ past participle) expresses near certainty about the past. 

[necessity] We must/have to take the test today. BUT We had to take the test yesterday.

[certainty] The professor must have been very pleased with everyone’s results because he was smiling when he handed back the graded tests.

NOTE: The exception to the above would be using must have (+ past participle) to state a requirement that must be met in order for additional action to be taken. In other words, necessary action was taken at some point in the past, and as a result, the party who performed that action may now proceed with his or her plan. Example: [from the University of Wisconsin webiste.]

Applicants must have earned at least 24 applicable semester credits prior to transfer. Applicants must have completed high-school-level algebra and plane geometry, college preparatory math, and two high-school years or two college semesters of the same foreign language.


  • Speakers use not only shortened forms (contractions) of must and have (got) to, but also reduced forms*. The reduced forms are not considered correct in written form. Examples: 

Must not = mustn’t (“You mustn’t tell anyone.”)

Must have = musta* (“You musta been really worried. Weren’t you?”)

Have (got) to = I’ve got to/ I got to/ I gotta* (“I gotta go.”)

Have to= hafta*  (“I hafta to.”) 


In the next posting, I’ll try to offer ideas for exercises and/ or an activity on this topic.


One Comment Add yours

  1. wendy says:

    this is awesome, I need to give this kind of topic to my students in my micro teaching class.. Could you help me to find listening exercise concerning to this topic???

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