I was taught that there is a difference in the kind of obligation one can express through 'must' and 'have to'. If I say

I must do this.

I imply that I feel an inner urge to do this, whereas if I say

I have to do this.

the obligation is somewhat external, coming from somebody else, not necessarily as an inner conviction.

I am proofreading a book and I must say that in written language I definitely prefer 'must' rather than 'have to'. Yet my friend tells me: 'If I say must I feel obliged, if I say have to it comes from the heart.' English is her mother tongue, not mine. I just wonder if my instinct is right. Thank you for your help.

PS: Does not have to sound more spoken language than must?

  • 1
    "have to" expresses an obligation due to external circumstances (nothing to do with the heart) e.g. To go to the USA, you have to have a passport.
    – Patrick D
    Dec 4, 2020 at 11:13
  • My friend spend a long time in the USA actually. I wonder if this is not an American influence on her...
    – fev
    Dec 4, 2020 at 11:17
  • I'd guess that there is the most separation (emotional content vs unmarked) in imperatives. "You have to make the decision now.!" though even there, they're pretty much interchangeable. In negations, of course, 'must' is used ('You must not smoke in the library'). And in formal contexts ('Students must pay course fees by Jan 28th'). Jan 3, 2021 at 15:24
  • @EdwinAshworth: So, you wouldn't say 'Students have to pay course fees by Jan 28th' because it is not formal enough?
    – fev
    Jan 3, 2021 at 15:34
  • 1
    It would be hyperprescriptive to say 'Have to' must be eschewed in formal texts (in present simple) but I'd probably not choose it very often. Passivised 'Care has to be taken ...' sounds impeccable, though. Jan 3, 2021 at 19:53

1 Answer 1


I am not sure about the exact grammatical meaning of each expression, but in everyday American English, "must" and "have to" are used interchangeably for both internal and external obligations. For example, "To obtain a driver's license, you must be at least sixteen years of age" and "I have to help my friend" both sound correct to me, yet they contradict the usage that you were taught.

  • You see, for me 'I must help my friend' is much stronger than 'I have to help my friend.' In the first statement I mean that it is my inner conviction that I should help him no matter what, whereas in the second, I have to help him because he is my friend, he is in trouble, etc. As for the driver's licence, I agree that 'must' sounds right here. My intuition tells me that for conditions one must fulfil in order to enjoy rights or services, we should rather use 'must', but this might be a different meaning altogether of the use of 'must'.
    – fev
    Dec 4, 2020 at 12:00
  • @fev I agree that "must" is stronger than "have to", but my point is that either can be used to describe either internal or external obligations. "I must help my friend because they are in trouble" and "I have to help my friend no matter what" are both correct. I think "must" is used a bit more often in legal writing because it is stronger and a bit more formal, but it would not be incorrect to use "have to" instead.
    – user407452
    Dec 4, 2020 at 12:34

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