# must / have to



## slow

Hi

Could does anyone explicate to me the difference between must and have to?

I have been reading something about it on the net but it doesn't make clear to me.

Regards

_<< Moderator note: Several threads with the exact same question have been merged, and the thread has been closed because none of the questions provided a specific sample sentence. Please refer to  the forum rules regarding context. >>_


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## Gabriel

Maybe because there is no difference?
At least, I use any of them to say the same sort of things:

We all have to/must die (inevitability)
Citizens have to/must be 18 years old or later to apply (requirements)
You have to/must do your homework (obligation)
It has to be / must be almost midnight (probability)

But only have to can be used in future or past tenses:
Why did you did that?  I had to do it.
If you accept, you will have to follow this agreement word by word.

But you also have:
What time was it when the phone rang? I must have been almost midnight / It had to be almost midnight (debe haber sido casi medianoche / debió ser casi medianoche)


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## Fritzybabe

Firstly let me say I am no expert.

I think the answer to your question might be the fact that English has evolved from many other languages, (French, Germanic, Latin etc.).

To have to is probably borrowed from Latin/French as in Spanish tener que whereas must comes from the German Mussen.

Any etymologists who know?

Fritzybabe.


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## Padawan

Yo creo que la diferencia más notable (si es que marca una diferencia) es que HAVE TO es más enfático que MUST. Es como si el que lo dijera estuviera más decidido a hacer algo que piensa que está obligado a hacer (moralmente).

Espero que te sirva


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## el_novato

Ahmmmm, tengo entendido que la expresión usada para enfatizar mas fuerte o mas claro, es MUST = HAVE TO, y que los dos tienen el mismo peso.  Por lo que no existe diferencia de nivel en ámbas; pero si lo que dices es correcto, pues es algo nuevo para aprender.

Me gustaría que alguien mas ahondara en este tema.

Saludos.





			
				Padawan said:
			
		

> Yo creo que la diferencia más notable (si es que marca una diferencia) es que HAVE TO es más enfático que MUST. Es como si el que lo dijera estuviera más decidido a hacer algo que piensa que está obligado a hacer (moralmente).
> 
> Espero que te sirva


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## JitterJive

slow said:
			
		

> Hi
> 
> Could does anyone explicate to me the difference between must and have to?
> 
> I have been reading something about it on the net but it doesn't make clear to me.
> 
> Regards


Hi Slow,
Could anyone explain to me the difference between _must_ and _have to_?  I have been reading something about it on the net but it doesn't make sense to me.

Give me the URL to the web page and I'll try to put it together for you.


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## el_novato

.                  . 



			
				el_novato said:
			
		

> Ahmmmm, tengo entendido que la expresión usada para enfatizar mas fuerte o mas claro, es MUST = HAVE TO, y que los dos tienen el mismo peso.  Por lo que no existe diferencia de nivel en ámbas; pero si lo que dices es correcto, pues es algo nuevo para aprender.
> 
> Me gustaría que alguien mas ahondara en este tema.
> 
> Saludos.






			
				Padawan said:
			
		

> Yo creo que la diferencia más notable (si es que marca una diferencia) es que HAVE TO es más enfático que MUST. Es como si el que lo dijera estuviera más decidido a hacer algo que piensa que está obligado a hacer (moralmente).
> 
> Espero que te sirva


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## slow

JitterJive said:
			
		

> Hi Slow,
> Could anyone explain to me the difference between _must_ and _have to_?  I have been reading something about it on the net but it doesn't make sense to me.
> 
> Give me the URL to the web page and I'll try to put it together for you.



Hi Jitterjive,

This one is what surface on the web page

Diferencia entre have + to + infinitivo y 'must' 

'Must' en su sentido de obligación, se usa para dar órdenes o para hacer que alguien o uno mismo cumpla con un cierto compromiso: 

You must stop smoking / Tiene que dejar de fumar (Dice el médico)

Cuando se trata de órdenes externas impuestas, (leyes, normas, etc) o dictadas por terceros, es más usual el empleo de 'to have to' 

The doctor says I have to stop smoking / El médico dice que tengo que dejar de fumar. 

En forma negativa, 'must not' expresa una prohibición. En cambio, 'don't have' to indica que algo no es necesario, es decir, que no existe obligación.

You mustn't listen to other people's conversations. 
No debes escuchar las conversaciones de otras personas.
You don't have to listen to the speech if you don't want to. 
No tienes que escuchar el discurso si no quieres.

is this right?

Regards


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## vesna

That's it! A very nice explanation. All the basics is there.
No se trata de que uno sea mas fuerte que otro.


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## el_novato

Thanks for the lesson, Slow.   

I have learned a something new.


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## atignirgal

In my opinion, must/ought/should = deber; have to = tener que

you have to [do such and such] = tienes que...
you must [do such and such] = debes...
you should/you ought to [do such and such] = deberías...
you must [be tired] = debes de estar cansado/estarás cansado


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## toniga

SLOW:

May I make some corrections?  Here they go:

"Could does anyone explicate to me ?"
"Could anyone explain to me...?"  Is it possible that some  do it for me?
Either could anyone explain... or
Does anyone explain, but not the TWO TOGETHER.  For questions you only need one auxiliary.

"but it doesn't make clear to me."
"but it is still not clear to me..."
"but it doesn't make any sense to me"
"but it doesn't make it clear to me" (sounds weird, though)

EL NOVATO:

"I have learned a something new"
I have learned something new" (without "a", something is indefinite by itself) : "I have learned a new thing"


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## slow

Thanks Toniga

You help me very much.

Regards


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## jacinta

Well...yes, I agree with the web page explanation but...with the negative use of "must" or "mustn't", it is rarely used.  (I'm speaking of American English so please excuse any differences in the language.)  Mustn't is replaced by shouldn't.  To be more emphatic, "Can't" is used.

"you mustn't smoke here" -rare    More common are:
"You can't smoke here"
"You shouldn't smoke here".

"You mustn't listen to other people's conversations". rare
"You shouldn't listen to other people's conversations" more common

As far as the positive use, must is absolutely used.  Must and to have to have the exact same meanings:

"Wow!  That must have hurt!"  or
"Wow!  That had to have hurt"

"You must have had a lot of work to do.  Is that why you're late?"

One more thing:  generally, "to have to" is more widely used than "must" but then again, they are both used and are correct.


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## el_novato

Gracias toniga




			
				toniga said:
			
		

> ...
> EL NOVATO:
> 
> "I have learned a something new"
> I have learned something new" (without "a", something is indefinite by itself) : "I have learned a new thing"


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## Manuela

In my humble opinion,

the main difference is that MUST is less used; it belongs to an older English.
We use you HAVE TO most of the time or more slangly GOT TO.
However I really liked SLOW's explaination


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## te gato

Manuela said:
			
		

> In my humble opinion,
> 
> the main difference is that MUST is less used; it belongs to an older English.
> We use you HAVE TO most of the time or more slangly GOT TO.
> However I really liked SLOW's explaination


Hola;
I agree....Pero...MUST is used when you want to be listened to more...."YOU MUST!!!" where as "you HAVE to" can be ignored more....
For example: When I tell my son "*you MUST"* clean your room, he knows that I am not going to negotiate the matter...When I tell him "*you HAVE"* to clean your room, he will do it when ever that day....I hope I have not confused anyone.
check ya later
karen


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## tuvir

there are a lot of explanations about these verbs but very confuse . Can somebody explain it  but very extensive? I have read a lot about this modal verbs but I would like other opinions. thanks


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## Mita

Hola Tuvir, 

La explicación que yo te daría es bastante breve: según lo que sé, must significa "deber" y "have to" significa "tener que". Y para mí "must" expresa un sentido de obligación más fuerte que el de "have to".
Ejemplo: You must eat -> Debes comer.
............You have to eat -> Tienes que comer. 

"Must" también puede significar "deber de", en un sentido de suposición. Por ejemplo:
A: Where is Anna? -> ¿Dónde está Anna?
B: She must be there -> Debe de estar ahí.

Ojalá que se entienda y te sirva 

Saludos,


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## Jhorer Brishti

Mita lo ha explicado bien y sucintamente. Quiero anadir que aqui en los estados unidos usar "must" para significar la primera definicion(asi tendria la misma definicion que "have to") no es muy comun. Pareceria un poco extrano(a menos que sea algo oficial, algo dicho por el presidente, las noticias,etc.), anticuado y se pensaria que tu estabas bromeando(es igual que el uso limitado casi invisible de "shall" aqui en EEUU).


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## gvergara

Otra diferencia, que es una de las más difíciles de entender, es que _have to_ se usa cuando es una obligación impuesta externamente (como una orden de otra persona, una regulación, una regla), mientras que _must_ se utiliza cuando se trata de una decisión personal.Ejemplo: 

_ _I *must *go and talk to the principal_. Acá, quien habla siente la responsabilidad moral, autoimpuesta, de ir a hablar con el director. Uso subjetivo.
_ _I *have to* go and talk to the principal_. Acá, alguien le dijo, le ordenó al hablante que debe ir a hablar con el director (puede que haya sido un profesor, el mismo director, un inspector, etc) No es una decisión de propia voluntad. Uso objetivo.

Saludos

Gonzalo


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## tuvir

MUchisimas gracias Gonzalo ésa es la explicación clara que quería


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## gvergara

De nada, nos vemos

Chao


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## jacinta

No es común decir "I must..." Se dice más, "I have to..." en cualquier situación.  Tienen el mismo significado.


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## gvergara

jacinta said:
			
		

> No es común decir "I must..." Se dice más, "I have to..." en cualquier situación. Tienen el mismo significado.


 
Hola Jacinta:
La verdad es que, reconociendo que en muchos casos _must_ y _have to_ son equivalentes, hay otros en los que debe(ría) hacerse una diferencia entre ellos. Uno de esos casos es el que ya expuse, el punto es que los nativos muchas veces no nos damos cuenta de las reglas que rigen nuestros idiomas y ahí surge la duda si una lengua debe hablarse como ordenan los libros de gramática o si lo correcto es aceptar al idioma como es hablado en el día a día por sus habitantes. Yo, mientras tanto, seguiré haciendo diferencias entre _must_ y _have to_....Saludos, nos vemos

Gonzalo


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## jacinta

Hola, Gonzalo,

No disputo ningún dato que nos diste. Es muy informativo.  Sólo que 
les hablo como nativa y digo cómo es en el habla diaria.  Es importante saber la gramática, es cierto, pero a la vez me gusta saber cómo se habla verdaderamente.  Creo que siempre que uno esté estudiando un idioma, quisiera saber cómo se dice en realidad, ¿no lo crees?

Saludos y buenas noches


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## gvergara

jacinta said:
			
		

> Hola, Gonzalo,
> 
> No disputo ningún dato que nos diste. Es muy informativo. Sólo que
> les hablo como nativa y digo cómo es en el habla diaria. Es importante saber la gramática, es cierto, pero a la vez me gusta saber cómo se habla verdaderamente. Creo que siempre que uno esté estudiando un idioma, quisiera saber cómo se dice en realidad, ¿no lo crees?
> 
> Saludos y buenas noches


 
Así es, estoy de acuerdo contigo. Nos vemos, Jacinta

Gonzalo


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## Fonεtiks

Gonzalo, interesante tu definición. Déjame ver si entendí:

must = sollten (autoimpuesta)
have to = sollen (impuesta)


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## gvergara

Fonεtiks said:
			
		

> Gonzalo, interesante tu definición. Déjame ver si entendí:
> 
> must = sollten (autoimpuesta)
> have to = sollen (impuesta)


 
Holas:
La respuesta a tu pregunta es no, aunque sí hay una correspondencia entre los modales alemanes e ingleses (observar, claro está, que nunca hay correspondencias perfectas entre idiomas). _Müssen_ corresponde, a grandes rasgos, a _must_, mientras que _sollen_ corresponde a _have to_ ¿Alguna vez te dijeron que _sollen_ se ocupa para reportar lo que otra persona dijo? Es por lo que explicaba arriba. Compara:

_ Dina, du *musst* einkaufen gehen.===> el hablante opina que receptor (Dina) debe ir de compras.
_ Dina, Vater hat gesagt, dass du einkaufen gehen *sollst*.===> el padre, no el hablante, opina que el receptor (Dina) debe ir de compras. Se ocupa _sollen_ por la misma razón que en inglés se ocupa _have to_ (orden externa rather than obligación moral autoimpuesta por el hablante).

Por su parte, el Konjunktiv II de _sollen_, _sollte_, _es un análogo de _should_.
Dina, du *solltest* einkaufen gehen (,weil dir alle Lebensmittel ausgegangen sind) ===> es un consejo, en vista que el hablante ve que a Dina se le acabó la comida, pero en ningún caso es una obligación. En inglés: Dina, you *should* go....
Espero haber sido claro, saludos y nos vemos

Gonzalo


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## Fonεtiks

gvergara said:
			
		

> ¿Alguna vez te dijeron que _sollen_ se ocupa para reportar lo que otra persona dijo?


Sí, muchas veces:
ARZT: "Du solltest/müsstest nicht so viel Fett essen"
_Später_
MUTTER: "Also, was hast der Arzt dich beraten?"
LEIDENDE: "er hat mir gesagt, dass ich nicht so viel Fett essen soll"


			
				gvergara said:
			
		

> Dina, Vater hat gesagt, dass du einkaufen gehen *sollst*.===> el padre, no el hablante, opina que el receptor (Dina) debe ir de compras. Se ocupa _sollen_ por la misma razón que en inglés se ocupa _have to_ (orden externa rather than obligación moral autoimpuesta por el hablante)


Por lo tanto _have to = sollen = be supposed to_, como te decía, o al menos, se aproxima. 


			
				gvergara said:
			
		

> Por su parte, el Konjunktiv II de _sollen_, _sollte, _es un análogo de _should_.
> Dina, du *solltest* einkaufen gehen (,weil dir alle Lebensmittel ausgegangen sind) ===> es un consejo, en vista que el hablante ve que a Dina se le acabó la comida, pero en ningún caso es una obligación. En inglés: Dina, you *should* go....


Entonces _must = müssen,_ o al menos, se aproxima
Había puesto must = sollten para hacer una analogía entre sollen y sollten, pero claro, müssen y sollten son distintos.


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## gvergara

Entonces _must = müssen,_ o al menos, se aproxima
Había puesto must = sollten para hacer una analogía entre sollen y sollten, pero claro, müssen y sollten son distintos.[/quote]

_Entonces must = müssen, o al menos, se aproxima_ *Correcto*
_must = sollten para hacer una analogía entre sollen y sollten, pero claro, müssen y sollten son distintos.[/quote]_ *No entendí*

Nos vemos, saludos

Gonzalo


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## ferdi

Existe alguna diferencia entre *HAVE TO* y *MUST*?


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## Edwin

ferdi said:
			
		

> Existe alguna diferencia entre *HAVE TO* y *MUST*?



Creo no hay mucha diferencía...es parecido a la diferencía entre deber y tener que


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## vince

Sí que hay una diferencia en lo negativo:


"I don't have to do it" = no tengo una obligación de hacerlo
"I must not do it" = es imperativo que no lo haga.

si alguien me pudiera explicar cómo se distingüen estos dos casos en español, sería genial.


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## Chris K

"Must" es mas enfático y menos común. Creo que nadie diría "I must walk the dog" en vez de "I have to walk the dog," aunque ambos son "correctos."


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## ferdi

en la manera negativa lo tengo claro, por ejemplo:
*don´t have to:* cuando algo no es necesario o importante.
*must not:* cuando algo está prohibido, no debes hacerlo.


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## Edwin

vince said:
			
		

> Sí que hay una diferencia en lo negativo:
> 
> 
> "I don't have to do it" = no tengo una obligación de hacerlo
> "I must not do it" = es imperativo que no lo haga.
> 
> si alguien me pudiera explicar cómo se distingüen estos dos casos en español, sería genial.



!Muy sutil!

Quizás la misma diferencía entre:

No tengo que hacerlo.
No debo hacerlo.


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## vince

de veras?
entonces,

si no tengo que hacer algo, aún puedo hacerlo.
pero si no debo hacer algo, y lo hago, algo mal me va a acontecer?


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## ferdi

Tengo entendido que así es


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## Guess What?

Must es obligación y have es mas indicacion.
You have to take the train to get there
you must arrive on time.


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## leukar

hello everybody,
lately I´m having some problems with the difference in use of must and have to, could somebody tell me his/her opinion please? Thank you very much


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## dropofrain

I was taught that when you use "must" the obligation comes from outside.
Eg: (The doctor to a patient): You must lose some weight otherwise you'll have serious problems.
However when we use "have to" the obligation comes from ourselves.
I have to lose some kilos if I want to wear this dress next week.
Although I have seen just the opposite explanation in some American grammars.


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## urciman

MUST:internal obligation; it depends on the speaker's feelings.
_You must be back home by 12:00_ (obligación impuesta por el hablante, el padre o la madre).
HAVE TO:external obligation( laws,agreements,other people's orders).
_I have to be back home by 12:00_( lo dice el chico o la chica pero la obligación le viene impuesta desde fuera, del padre o la madre).
ESpero que te sirva.


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## FromPA

I've never heard of this internal/external obligation concept.  To me, the two have the same meaning, but the doctor is more likely to tell the patient "you have to lose some weight"  rather than "you must..." simply because "have to" is more colloquial.  "You must" seems like a phrase you see in contracts or that you hear used in old movies.


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## Sallyb36

I agree with FromPA, they are interchangeable.


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## MiCorazonEstaEnCadiz

I also agree. They have the same meaning.


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## leukar

thank you very much, but the problem is that although I´ve always heard people use them with the same meaning my daughter´s teacher only accepts *have to* for laws and rules, and *must* for the other obligations, besides, I learnt just the opposite.
So, my question is how we should use them if we had to attend an official examination, for example.


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## zetem

"Must" and "have to" are sometimes interchangeable and have the same meaning (more often in AmE than in BE), but sometimes they are not, as in the following examples:
(1) You must submit your report before 3 p.m. today. (= I want you to do it) The speaker has the authority to give orders.  
(2) You have to submit your report before 3 p.m. today. The obligation comes from outside, not from the speaker. (someone else with higher authority, or it is by law, or by some other rules or obligations.) The speaker only gives the information of what is to be done and how. 
(3) I must stop smoking (= I want to); "Have to" cannot be used for this meaning.
(4) I must see the dentist (= I have a toothache). 
(5) I have to see the dentist at 3 p.m. (= I have an appointment)
(6) You mustn't tell George (= Don't tell George)
(7) You don't have to tell George (= Tell him if you like, but it is not necessary)


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## geostan

> *zetem*
> (3) I must stop smoking (= I want to); "Have to" cannot be used for this meaning.


I see nothing wrong with using "have to."



> *zetem
> *(5) I have to see the dentist at 3 p.m. (= I have an appointment)


It could mean that, but it doesn't have to. I might say this even if I don't have an appointment.

As for the question about examinations, it is unfortunate, but whatever is prescribed by the examining authority has to be followed, even if it does not reflect reality

Cheers!


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## zetem

geostan, it is you choice to say what you want to and how you want to, your listener will understand you (sort of),  but here, I think, we are talking about the usage generally accepted by at least some grammarians. In informal American English, the distinction between the usage of "must" and "have to" is disappearing fast, and it is possible that in the future one of these terms will become redundant.


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## FromPA

zetem said:


> geostan, it is you choice to say what you want to and how you want to, your listener will understand you (sort of), but here, I think, we are talking about the usage generally accepted by at least some grammarians. *In informal American English, the distinction between the usage of "must" and "have to" is disappearing fast*, and it is possible that in the future one of these terms will become redundant.


 
I think it's long gone.  As I said above, the only place I see "must" is in contracts, so the fine distinctions you're drawing between the two would be completely lost on most Americans.


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## sepilicious

In the positive they are very similar. "Must" is used more frequently when we are talking about a logical conclusion rather than necessity/obligation.
For example: "Shelly worked 10 hours today. She must be really tired" (Since Shelly worked so much, I can deduce that she's tired)

In the negative there is an important difference:
- You don't have to help Shelly - lack of necessity (e.g. Shelly can do it by herself. Your help is not necessary)
- You must not help Shelly - prohibition (You are not allowed to help Shelly. She needs to learn to be independent. Or maybe she is my enemy...)


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## SevenDays

I’ve always thought there is a difference.  To me, “must” reflects a stronger obligation than “have to.”
 
I have to go to church.  (I really don’t want to, but my parents said I have to go).
I must go to church.      (It is urgent that I go. I need to confess, I don’t want to miss mass, etc.  It is a moral obligation.)
 
Also, must has no past form.
 
I had to go to church last Sunday.
 
For future obligations, it seems natural to use will have to rather than must
 
One day, I will have to go to church.
 
But I wouldn’t claim that these uses are universally accepted, or normally used.  
 
Cheers


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## sepilicious

Must does have a past form: you use have + participle

"Where is the car?"
"Jill must have borrowed it"

"Sam must have been very tired after he worked for ten hours yesterday"

In the past we only have "logical conclusions" and not necessity/obligation


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## dtbrooklyn

Just to add my two cents to this little debate.  As an American I almost never use "must", except in the cases of logical conclusions "no one answered the phone so she must not be at home", and with the negative where "must not" and "don't have to" have very different meanings. In terms of obligation or advice I use "have to" 99% of the time. I completely agree with the other poster who stated that differentiation between the two words that states one comes from an outside source and the other from the speaker has long since been forgotten in the US.  Honestly, when I hear "must" it sounds formal, stodgy, and quite British "You simply must try the cucumber sandwiches".  ha.... to these ears it sounds pretentious.


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## SevenDays

sepilicious said:


> Must does have a past form: you use have + participle
> 
> "Where is the car?"
> "Jill must have borrowed it"
> 
> "Sam must have been very tired after he worked for ten hours yesterday"
> 
> In the past we only have "logical conclusions" and not necessity/obligation


 
I said “must has no past form,” so let me point out that I was referring to the modal verbs “must” and “have to” when used to convey *necessity/obligation*, but I suppose I should have made that clear.
When used in that specific context (*necessity/obligation*), “must” doesn’t have a past form.  To refer to the past, you use “have to” (in the proper past form, of course).
 
I _had to_ get up early yesterday.
I _must_ get up early yesterday. (wrong)
I _must_ got up early yesterday. (wrong)
 
In other words, _had to_ is used to express _past_ obligation.
 
In the examples you cited, you are using “must” with the perfect infinitive (have + participle) to express *certainty* (or logical conclusion) about a past event.  It is a different context.
 
Cheers


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## spencerfox7

I often enjoy reading the input and the opinions of others because it can sometimes spark thoughts I would not have otherwise come up with. However, regarding contemporary American English, which I know and understand very well, there is not a whole lot of useful information in this thread.

I am not sure of the origen of that whole internal/external idea, but I have never heard of it, and it is in no way inherent in the language here. Perhaps that idea existed in Europe many centuries ago?

I agree with SevenDays that "must" has an element of obligation that is a little bit stronger than "have to." I also agree that "must" is a little bit more formal; "have to" is much more common in everyday conversation.

Again, things may have been different in the past, or they may even be different now in Canda or Europe; I am not sure. "Must" may sound better or work a little better in certain contexts, and vice versa, but the difference between the two is very, very small. In most instances, you could probably say that it is negligible. A situation or concept does not exist in which the two cannot be reasonably interchanged. There is no doubt in my mind that in the future, the two words will literally have no difference other than spelling.

In association with today's American English, the difference between "must" and "have to" is definitely not something with which you should worry yourself.

Good Luck!


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## BocaJuniors

FromPA said:


> I've never heard of this internal/external obligation concept. To me, the two have the same meaning, but the doctor is more likely to tell the patient "you have to lose some weight" rather than "you must..." simply because "have to" is more colloquial. "You must" seems like a phrase you see in contracts or that you hear used in old movies.


 
Same here, never ever heard of any obligations, not even in college. In every day use, they mean the same thing.


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## Argónida

urciman said:


> MUST:internal obligation; it depends on the speaker's feelings.
> _You must be back home by 12:00_ (obligación impuesta por el hablante, el padre o la madre).
> HAVE TO:external obligation( laws,agreements,other people's orders).
> _I have to be back home by 12:00_( lo dice el chico o la chica pero la obligación le viene impuesta desde fuera, del padre o la madre).
> ESpero que te sirva.


 
That's exactly what I was always thaught in my English lessons. Are my teachers and books wrong then?

Regards.


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## FromPA

Argónida said:


> That's exactly what I was always thaught in my English lessons. Are my teachers and books wrong then?
> 
> Regards.


 
Yes, they are - if you are in the US.  I don't know what the rest of the English-speaking world thinks.


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## zetem

Argónida, "That's exactly what I was always thaught in my English lessons. Are my teachers and books wrong then?"

It is very likely that your teachers taught you the grammar of standard British English. If so, your books are good but it is still wise to know and appreciate the differences between American and English grammar. It is always good to say what usage (American or British) we are talking about, before asking the questions of what is right or wrong. Regards.


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## Forero

_Must_ = "deber" o "deber de" (en tiempo presente).  _Must_ is a defective verb, so:

"Debe": _musts_ , _must_ .
"Ha debido": _have musted_ , _must have_ .
"debería": _would must_ , _must_ .

_Have to_ = "tener que" (en tiempo presente). _Have to_ is not defective, but the _to_ acts like part of the verb and cannot separate from the _have_/_has_.  The final _v_/_s_ sound is devoiced.

_M__ust__ not_ do something means "has to not" do it, not "does not have to" do it.

_Must_ can mean "deber de".  When _must_ means "deber de", _must not_ means we can surmise that something is not so, not that we cannot surmise it is so:

_That must be Tina._ = _That has to be Tina. _= Eso debe de ser Tina.
_That must not be Tina._ = Eso no será Tina. [No puede ser Tina.]

Otherwise, _must_ and _have to _/ _has_ _to_ are practically equivalent:

_What must I do to be saved?_ = _What do I have to do to be saved?
_
I say "practically equivalent" because context can make a big difference.  In some contexts, for example when referring to duty, _must_ can be stronger, almost as if "shall" were part of the meaning.


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## zapateado

I like that  have to  literally shows the idea of something being there to do, having to do, I have it to do. (In Spanish there is the word quehaceres, lit. those to do, very close to have to, meaning chores or even assignments)  And must for me has the feeling of necessity.  Interestingly  have to  is often pronounced as if it were haf to.


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## Argónida

zetem said:


> Argónida, "That's exactly what I was always thaught in my English lessons. Are my teachers and books wrong then?"
> 
> It is very likely that your teachers taught you the grammar of standard British English. If so, your books are good but it is still wise to know and appreciate the differences between American and English grammar. It is always good to say what usage (American or British) we are talking about, before asking the questions of what is right or wrong. Regards.


 
I know that the English we learn here in Spain is mainly British English, but I'm not sure if the distinction between "must" and "have to" I've been taught is due to geographical differences, since in this thread British speakers have said that "must" and "have to" are interchangeable (post 5).

Regards.


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## zetem

Argónida, the BE you've been taught is known as Standard British English, as well as Written English, International English. You can hear that English on BBC (News) and is typical for professional middle class in GB. The grammar books you have are based on this English.  I suspect that some opinions you read are the usage typical for informal British English. I live in Canada and rarely use "must" in speech, myself. My point is that one should first learn Standard British English (from grammar books) and then twist his knowledge and use any way he likes. I have a few educated coleagues who would say "I says", or "he don't", but they will always write "I say" and "he doesn't". This little game may be good for the natrives but the learners should stick to the knowladge from grammar books. Just my opinion. Regards
PS: Note that I said "one ...he" (informal). Standard BE usage is "one ...one".


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## bluejazzshark

Argónida said:


> I know that the English we learn here in Spain is mainly British English, but I'm not sure if the distinction between "must" and "have to" I've been taught is due to geographical differences, since in this thread British speakers have said that "must" and "have to" are interchangeable (post 5).
> 
> Regards.



We have to be careful here. "must" and "have to" have different uses, but when it is being used to express *obligation* then they *are* interchangeable in the UK.

Don't forget that the negatives mean totally different things. "Don't have to" means you are free from obligation and "must not" means you are prohibited from doing something.

I'd also say that "must" as obligation is more formal than "have to". "have to" is used far more frequently in the spoken language than "must". It's like the difference between saying "tienes que hacer algo" and "Es imprescindible que hagas algo".

Also, "must" is used for "supposition" whereas "have to" isn't.

There are only two chocolates left. John must have eaten one. CORRECT
There are only two chocolates left. John had to have eaten one. WRONG

Finally, I think this distinction between internal and external obligation is a load of rubbish to be frank. "I have to go to work every day" = "I must go 
to work everyday."

- Blue.


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## zetem

bluejazzshark:  "I have to go to work every day" = "I must go 
to work everyday."

Suppose you say to your boss "I have to work every day". How, in your opinion, your boss should understand this statement? If I were your boss, I would say "No, you don't".


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## leukar

thank you very much for all your explanations, they are really useful
regards


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## Argónida

zetem said:


> Argónida, the BE you've been taught is known as Standard British English, as well as Written English, International English. You can hear that English on BBC (News) and is typical for professional middle class in GB. The grammar books you have are based on this English. I suspect that some opinions you read are the usage typical for informal British English. I live in Canada and rarely use "must" in speech, myself. My point is that one should first learn Standard British English (from grammar books) and then twist his knowledge and use any way he likes. I have a few educated coleagues who would say "I says", or "he don't", but they will always write "I say" and "he doesn't". This little game may be good for the natrives but the learners should stick to the knowladge from grammar books. Just my opinion. Regards
> PS: Note that I said "one ...he" (informal). Standard BE usage is "one ...one".


 
Thank you, *zetem*. I understand now and I agree with you.




bluejazzshark said:


> We have to be careful here. "must" and "have to" have different uses, but when it is being used to express *obligation* then they *are* interchangeable in the UK.
> 
> Don't forget that the negatives mean totally different things. "Don't have to" means you are free from obligation and "must not" means you are prohibited from doing something.
> 
> I'd also say that "must" as obligation is more formal than "have to". "have to" is used far more frequently in the spoken language than "must". It's like the difference between saying "tienes que hacer algo" and "Es imprescindible que hagas algo".
> 
> Also, "must" is used for "supposition" whereas "have to" isn't.
> 
> There are only two chocolates left. John must have eaten one. CORRECT
> There are only two chocolates left. John had to have eaten one. WRONG
> 
> Finally, I think this distinction between internal and external obligation is a load of rubbish to be frank. "I have to go to work every day" = "I must go
> to work everyday."
> 
> - Blue.


 
Thank you, *Bluejazzshark*. Fortunately, this time my books agree with your explanation about other uses of "have to" and "must" and about its negative forms.
Then the distinction between "must" and "have to" is not a geographical but a formal/informal language matter. I think something similar happens in Spanish, because we usually say "tener que" rather than "deber" in everyday speech.

Regards.


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## Forero

For surmising, I think _must_ and _have to_/_has to_ are equivalent (except for the defective verb issue):

_There are only two chocolates left. John must have eaten one._ CORRECT.
_There are only two chocolates left. John has to have eaten one._ CORRECT, same essential meaning.
_There were only two chocolates left. John must have eaten one. _CORRECT. _Must_ has no past tense, so present substituted for past.
_There were only two chocolates left. John had to have eaten one. _CORRECT. _Have_ is not defective, so tenses can match.


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## zetem

According to my grammar book (see below), "have to" and "must" are interchangeable (with the same meaning) only in two cases:

(A) Logical Necessity
(1) There must be some mistake (BE). There has (got) to be some mistake (especially in AmE). The speaker has drawn a conclusion from things already known or observed. "Has to" is considered here more emphatic than "must".
(B) Root Necessity (no human control)
(1) To be healthy, a plant must (has to) receive a good supply of both sunshine and moisture.

There is an interesting note regarding "Obligation". I quote "Some native speakers do not recognize the distinction between 'self-obligation' (I must) and 'obligation by external forces' (I have to)" End of quote.

Ref: A comprehensive Grammar of the English Language", Randolf Quirk, et al. Longman, 1986.


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## zapateado

zetem said:


> According to my grammar book (see below), "have to" and "must" are interchangeable (with the same meaning) only in two cases:
> 
> (A) Logical Necessity
> (1) There must be some mistake (BE). There has (got) to be some mistake (especially in AmE). The speaker has drawn a conclusion from things already known or observed. "Has to" is considered here more emphatic than "must".
> (B) Root Necessity (no human control)
> (1) To be healthy, a plant must (has to) receive a good supply of both sunshine and moisture.
> 
> There is an interesting note regarding "Obligation". I quote "Some native speakers do not recognize the distinction between 'self-obligation' (I must) and 'obligation by external forces' (I have to)" End of quote.
> 
> Ref: A comprehensive Grammar of the English Language", Randolf Quirk, et al. Longman, 1986.



I like this very much.  It is my sense of it, and it is laid out nicely.


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## Ynez

Forero said:


> _Must_ = "deber" o "deber de" (en tiempo presente).
> 
> "debería": *SHOULD/OUGHT TO*
> 
> _Have to_ = "tener que"
> 
> 
> _That must be Tina._ = _That has to be Tina. _= DEBE SER TINA/DEBE DE SER TINA/TIENE QUE SER TINA
> _That must not be Tina._ = NO DEBE SER TINA/NO DEBE DE SER TINA/NO SERÁ TINA



I made some changes, Forero.


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## Ynez

zetem, modern Grammar books (and I'm referring to British ones) do not mention that difference about internal/external obligation. If you think of it, that only causes confusion. It seems the same happens when teaching Spanish. 

I'll give you examples in Spanish.

P1- ¿Por qué no te montas en el autobús?
P2- Tengo que esperar a una amiga.


The idea of that "tengo que" is internal from my point of view. We could also say "debo esperar...", but the normal is "tengo que" and "have to" in English, if I'm not wrong.


"Deber" is used for instance in paperwork, in an office, a bank, etc.:

P1- Hola, buenas tardes. ¿Me podría explicar qué hay que poner en esta casilla?
P2- Ahí debe usted poner su número de la Seguridad Social.

If that person talked to you as "tú", he/she would probably say:

P2- Ahí tienes que poner el número de la Seguridad Social.

But for this the first example is more normal.

In English, "must" is used for these formal instructions (correct me if not) and it is not intrinsecal, but just formal.


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## zetem

Forero, When must is used for logical necessity, the opposite of must is cannot:

_That must be Tina._ = _That has to be Tina_.
_That cannot be Tina_. (not "must not")

You can use "must not" to negate must statements in examples when you urge someone to do, or not to do, something.
You must accept the idea that you are not loved.
You must not accept the idea that you are not loved.


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## urciman

Hello, YNEZ modern grammarians do mention that difference.Have a look at *Practical English Usage By Michael Swan,English Grammar by D. Beaumont & C. Granger,...*
Un saludo.


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## zetem

Ynez, I am a beginner in Spanish, and the difference between tener que and deber is as confusing to me as is the difference between "must" and "have to" to Spanish students of English. The books I use for references are at least 20 years old, and I muself suspect that they may be in some respects out of date. I am aware that some "modern" BE gramamar books offer different explanations and meanings from the ones in my books. I am aware that today BE is much closer to AmE then it was 20 years ago, but I still believe that Written English, or Formal English has not changed much. On the other hand, even 20 years ago there were quite a few grammar books written for different levels and learners, which would give different explantions and meanings for the same problems. Out of frustration, I bought Quirk's grammar (costed me more than $200 dollars at that time), because I was tired of all these books. This book is still the best, I think and hope.

To answer your question, "must" tends to be more formal than "have to" when you can use one or the other. For example, your boss may say "You have to do this by 3 p.m." (instead of "you must"), in an attempt to suggest that he is just your colleague and is helping you to do your job. But make no mistake, this is a formal order. Regards.


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## Ynez

zetem, believe me that, in general, Spanish and English are very similar at this (must= deber/have to= tener que). To explain farther than that we need to go through particular examples, but I've heard the "internal/external obligation" explanation in English and Spanish (so it is the same idea) and I find it misleading in both languages. 

urcima, _Practical English Usage_ is a great book, but it is not new. I don't know the other one.


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## BrokenButterfly

Hi! 
I just watched a lesson about modals..but there's something I don't have clear yet 
The differences between "must" and "have to"

I know both are used to express obligation.. but I think is more than that

Here in the grammar book says..

_Must+infinitive is used for strong obligations which express authority of the speaker or writer_
_Have to+infinitive is used for strong obligations which express the authority of a third person_


I think both can be used to express obligation when speaking of yourself
for example XD


I have to lose a couple of kilos this month. (this may not be an order from a third person)


Please write examples if possible, Thank you ^^


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## gengo

To me, they both have the same meaning, but their register is different.  "Have to" is more informal and colloquial.  Also, we use "must" in a different sense, to express probability.

I have to go.  (Tengo que irme)  informal and natural
I must go.  (Tengo que irme) very formal
You must be thirsty.  (Debes de tener sed)


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## flyingcabbage

Estoy de acuerdo con lo que dijo Gengo. *Must* es un poco más formal, y tiene también un segundo sentido (depende del contexto, claro).

Pero también: *Must sólo existe en el presente* (y el futuro de una tal manera), no existe ninguna otra conjugación. 

No se puede decir "_Last week, I must finish that essay_"  (hay que decir "_Last week, I had to finish that essay_" )  o _"If I got a pet dog, I would must walk it every day" _ (hay que decir "_If I got a pet dog, I would have to walk it every day _).


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