Must vs Have to

The Uses of Must and Haveto

The modal auxiliary must, and the semi–modal, have to, express the same meaning. We use both terms to express compulsion, obligation or necessity in the presentOpens in new window or future tenseOpens in new window.

Sometimes it doesn’t matter which one of the pair we chose to use. Although must is personal and as a result, it is appropriate when we share personal feelings. Have to is considerably impersonal, we use it to express facts or factual related issues.

Survey the difference in the following expressions:

Must
  • You must do something
    → (says ‘the speaker’ because it is necessary)
  • She’s a really nice person. You must meet her.
    →(says I ‘the speaker’ because it is necessary)
Have to
  • You have to do something. (because of a rule)
  • You can't turn right here. You have to turn left. (because of the traffic system)

However, in cases of questions Opens in new window and negative sentences Opens in new window with ‘have to’, we usually use either member of this group ‘do/does/did’, as the following example sentences illustrate:

  • What do I have to do to get a driving license? (not ‘What have I to do?’)
  • Why did you have to go to hospital?
  • Gretchen doesn’t have to work on Sundays.

Note the meanings in the following expressions:

  • Mustn’t have to do something →means (It is not necessary to do it.)
  • Don’t have to do something →means (Don’t need to do it.)
  • I promised I would be on time. I mustn’t be late →means (I must be on time.)
  • I’ve cancelled the trip. I don’t have to visit Memphis just yet →means (I don’t need to be there.)
Some Examples of Have to
  • I have to resume at the office by 9 a.m. (Because it is in my terms of employment)
  • He has to catch the 2:00 o’clock train.
  • You have to obey the traffic rules.
  • We have to obey the doctor’s advice.
  • We have to stop late night’s meals according to the doctor’s recommendation.

Some Uses of Must

1.  Uses of Must to express Obligation:
  • We must express respect to our elders.
  • You must obey your parents.
  • You must build a relationship with God.
  • You must study your school works.
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2.  Uses of Must to express Compulsion:
  • We must be there on time.
  • You must make the delivery before noon.
  • We must schedule a meeting to address this issue.
  • You must cook dinner tonight.
3.  Uses of Must to express Determination:
  • We must get through the examination.
  • We must bring home the trophy.
  • This term I must make mum and dad proud.
  • I must stay true, be myself, and put God first in everything.
4.  Uses of Must to express Conviction:
  • She must be back shortly afterwards.
  • Dad must be home by now.
  • It must be morning in California.
  • I must excel in flying colours.
Important Hint!  

Note that the past tense Opens in new window of ‘must’ is ‘had to’ and the future tense Opens in new window is ‘will or shall have to’. Ponder the following expressions:

  • We had to wait for them for two hours. (Past Tense)
  • You will have to reach the station by 3:50 p.m. to catch the 3:55 p.m. train. (Future Tense)

Must is not used in sentences that convey interrogative Opens in new window or negative sense Opens in new window. The expression “Must have” indicates the meaning of a past or completed action. Consider the following:

  • Gretchen must have finished cooking by now.
  • It must have been past mid-night when Daddy returned home

Mustn’t is used to express prohibition. Consider also the following:

  • He mustn’t come back here again.
  • You mustn’t disobey your parents.

Mustn’t also tends to express compulsion, obligation, etc., as the examples illustrate:

  • Students mustn’t skip classes.
  • You mustn’t take more than you give.