What's the difference?

[LarryLatham]

Mmmmm, no! I just got my Larson-Freeman grammar book back*, and checked what she says about must and have to. Unfortunately she's not very clear on the subject. She points out that, "You must not go", and "You don't have to go" are clearly different, as "the modal is a prohibition, while the phrasal form offers the addressee a choice." (p.144) What is obvious to me, but Larson-Freeman doesn't say, is that a prohibition clearly has to come directly from the speaker, or from someone or something the speaker is representing as an agent.

L-F also reminds us that in North American speech, have got to is most often reduced to gotta, and is most often used to express affect on the part of the speaker. [I must admit I don't really quite understand what that means. I suppose it means an expression of emotion or feeling, as in, "You gotta lend me five bucks!", especially when the gotta is emphasized as I've done in this example.]

She also points to a 1983 unpublished master's thesis by a S. L. Melrose at UCLA suggesting that "most native American speakers reserve the use of must for expressing inference (present and past):

You must have the wrong number!
John must have been joking when he said that." (p.150)

Melrose, in her study, also concluded that "have to is used in speech to express both external and internal social necessity" (p.150). This tends to contradict my view of the matter, as I believe use of have to expresses an external necessity, if what is meant by that is that the speaker conceives, at the moment of speaking, that the source of necessity resides outside his control. In opposition, in my view, must is selected by the speaker who believes, momentarily, that he is himself the source of social necessity.

But who cares!

Larry Latham

*The Grammar Book, Marianne Celce-Murcia and Diane Larson-Freeman, 2nd Ed., 1999, New York, Heinle & Heinle.