Dave's ESL Cafe's Student Discussion Forums

[Andie]

I'm looking for clear examples to illustrate the difference between "have to" and "must". It is clear to me that you use "have to" when there's an obligation that is imposed from outside (laws-rules), whereas "must" expresses what the speaker thinks is necessary. But browsing through different books, I've found examples such as, "In England you must drive on the left." Examples like these ruin my explanation contrasting the external-internal point. I wonder if anyone can help me. Thanks!

[lotus]

A really good question Andie,

It all depends on individual preference. But, my instincts sense that there may be some common instances where one might be used over the other. It's really hard to pinpoint, but I'll give it a try.

"Must", I believe, is used when you are commanded or forced by an outside entity to do something that you don't necessarily want to do.

"Have to", I think, is used when you yourself have decided that you should do something (even though you may not want to) to mitigate a possible negative consequence.

Here are some examples:

I have to study to get good grades. (your personal choice to study hard)
I must study to get a good grade. (you're scared someone might give you a bad grade)

In England, I must drive on the left side. (a law imposed upon the driver)
In England, I have to drive on the left side. (a good decision by the driver)

I have to get to the theatre on time. (you simply don't want to be late)
I must get to the theatre on time. (if you're late, they might not let you in)

We must be kind to others. (a global mandate, the consequences would affect everyone)
We have to be kind to others. (a personal edict, we couldn't live with ourselves otherwise)


--lotus

[Andie]

Lotus,

Thank you so much for your answer, but now I'm a bit confused... You're saying exactly the opposite to what I said!!

What about Michael Swan's examples?

I must make an appointment with the dentist. (Internal obligation: I've got toothache.)
I have to see the dentist tomorrow. (External obligation: I have an appointment.)

So, you can't say that "must" is used EXCLUSIVELY when there are outside rules. And it is at this point that I get confused: can "must" be used with things both coming from inside and outside the speaker? How do you explain this to your students? It's rather confused!

Still I can't plan my class because I don't know how to go about this difference.

Thank you anyway!!

[alan.es]

i know it's no help to you, Andie, in planning your class but I'm quite pleased that other teachers have the same dilemma as I have had.

I use 'must' for outside obligations - by someone else, teacher, police, parent etc.

- and 'have to' for internal obligations - when the person themselves sees the sensible necessity to do it.

Every textbook that I've used and read always says the opposite.

I've always taken a 'practical' view with students and told them to learn both - the book way for exams and 'my' way for speaking English.

The difference betwen them is very fine and often confused or ignored (grammatically) by native speakers. As an old hand at teaching and in years, I often think that sometimes these grammatical explanations are very finely drawn and not really worth spending too much time on.

The use of 'must' and 'have to' in the tenses is much more fundamental and worth the time.

[Andie]

It's weird, but I never had any queries when using either "have to" or "must". It was only when I was planning my class that I realised that I didn't know how to explain the difference between them! But if Alan.es says that even native speakers aren't sure... then I don't feel quite bad! Anyway, I've decided to stick to the way I've always used them and tell my students that the difference is a bit blurred. Thanks anyway!

[LucentShade]

I don't know if this external vs. internal obligation rule is used by native speakers. To me, it's just a question of formality: "must" has a more formal tone than "have to" (or "got to," "gotta," etc.), so it's used in "legal" talk, rules, or signs. However, the difference between the negatives, "don't have to" and "must not" is very clear.

[alan.es]

I agree completely that the difference between the negatives is very clear and needs to be known well.

Must not : a prohibition

Don't/doesn't have to : not a prohibition. It means "don't/ doesn't need to do so - only need to do so if the person wants to do so.

[MrPedantic]

I also find the internal/external distinction slightly at odds with usage:

1. In England, you have to drive on the left (external requirement).
2. I enjoyed that! We'll have to do it again some time (no external requirement).

Also, "must" seems to convert quite happily into "has to", e.g. in reported speech:

3. "No, I'm sorry, I must go. I have to be home by twelve." (internal + external)

[Later.]

"What happened to MrQ?"
"Oh, he said he had to go. He has to be home by twelve."

(Here, we can't tell whether MrQ was subject to an external or internal requirement "to go".)

MrP