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To me "I must help her" sounds wrong. I feel that I would rarely say this.

On one website they say that 'must' is more for personal obligations (e.g. I must help my mother.) and that 'have to' is for external obligations (e.g. my boss says I have to finish the report.)

Is it that simple (and vague)? Or does anyone have a better explanation?

Istable
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3 Answers3

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Mmmm, that's a subtle distinction that I think the website is inventing or imagining. To my ear, "must" is simply more formal.

Michael Lorton
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  • I concur, on both counts. – Brian M. Scott Sep 15 '11 at 08:19
  • @Malvolio that's how I feel as well. I just don't want to step into a classroom and say "in my opinion" and have no proof that I am correct! – Istable Sep 15 '11 at 08:23
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    In matters of connotation, I don't know what else you can do -- short of assembling a panel of experts -- other than say "in my opinion, as a native speaker, ..." Actually, I just got an official english.SE t-shirt in the mail today, so I guess you could try, "According to a guy wearing a convincing t-shirt..." – Michael Lorton Sep 15 '11 at 08:30
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    @Malvolio: I want a t-shirt that says "According to a guy wearing a convincing t-shirt ..." – Peter Shor Sep 15 '11 at 13:12
  • Agreed; I would hardly ever use "must" in ordinary conversation, unless referring to an attic. – JeffSahol Sep 15 '11 at 13:19
  • I agree. Compare "I have to go to the bathroom." with "I must visit the lavatory." If you switch the verbs in these sentences, it sounds a bit wrong to me. – Peter Shor Sep 15 '11 at 13:36
  • Why isn't "I have to" so formal? – Rookie Programmer Aravind Apr 02 '12 at 15:04
  • I don't know if there's ever a real answer to a usage question starting with "why". It seems that constructions that repurpose existing words ("have to", "used to") often are considered less formal than the auxiliary words that they replace, but that may just be an artifact of the way they were coined. – Michael Lorton Apr 02 '12 at 22:04
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they say that 'must' is more for personal obligations.

That is not true; when somebody says "you must show your ID card," it is referring to an external obligation (e.g. by a law) not to an obligation you personally have because your ideas.

apaderno
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For me "I have to" can transport a unwillingness to do the task.

Sorry I can't come. I must help my Mum.

This is more formal and the speaker is more or less happy to help.

Sorry I can't come. I have to help my Mum.

More informal and can express that the speaker isn't happy with helping.

Portree Kid
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