# can't / musn't [mustn't]



## jmalguacil

Hola, no entiendo muy bien la diferencia entre musn´t y can´t de prohibición.
¿Qué diferencia hay, por ejemplo, entre estas dos oraciones?
- You musn´t cross the road with red traffic lights.
- You can´t take photos using a flash in this museum.
En ambas, hay prohibición, ¿son iguales?


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## toc

You mustn't = no debes / no se debe

You can't = no puedes / no se puede


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## zelan

A lo mejor en la primera, además de prohibición, hay otra cosa, y es que el sentido común te dice que si pasas en rojo te pueden atropellar, no debes porque pones en peligro tu vida y no se puede tampoco porque está prohibido.

Por ejemplo, pregunto yo, si en una playa está prohibido el top less sería "*you can't go topless*", simplemente, no se puede. Hay una orden exterior que lo impide. Pero si vas a una playa nudista sí que puedes.
En esa misma playa hay bandera roja. Entonces *you mustn't swim*. It is dangerous (and also forbidden). Even if it wasn't a red flag you mustn´t.

En esa misma playa hay bandera verde, pero no sabes nadar:
*You can´t swim*. No puedes , no por una orden externa sino porque no sabes.
Si están arreglando la playa y no está permitido bañarse, pero *no es peligroso*:
No danger for you but maintenance work and forbidden:
*You can´t swim*.

Is that correct?


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## chamyto

jmalguacil said:


> Hola, no entiendo muy bien la diferencia entre musn´t y can´t de prohibición.
> Qué diferencia hay, por ejemplo, entre estas dos frases?
> - You musn´t cross the road with red traffic lights.
> - You can´t take photos using a flash in this museum.
> En ambas, hay prohibición, son iguales?


 
You mustn´t cross the road with red traffic lights= Prohibition, it usually comes from law or government.

You can´t take photos using a flash in this museum= The prohibition comes from norms of the museum.


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## Tazzler

En realidad, _can_ no se utiliza para permiso y hay que utilizar _may_. De hecho, la primera frase me suena más leve, casi como una sugerencia. Además, la contracción _mustn't_ es un poco antigua. Ya no se utiliza con frecuencia. Pero la primera frase me suena como si una niñera estuviera regañando a un niñito.


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## chamyto

No estoy de acuerdo en lo que te refieres a lo de _mustn´t_ al menos en BE.

Vamos a ver: Explícate en qué sentidos se usa _may  _en vez de _can _como permiso, pues no es en todos los casos.


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## toc

chamyto said:


> No estoy deacuerdo en lo que te refieres a lo de _mustn´t_ al menos en BE,


Tienes razón, pero es mucho más común que se use con el sentido de suposición (p.ej. "John mustn't be at home" - "John no debe de estar en casa") que para denotar obligación/prohibición (que sí puede sonar un poquito old-fashioned, al menos para mí).



Tazzler said:


> Pero la primera frase me suena como si una niñera estuviera regañando a un niñito.


A mí también.


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## Miinniie

Hello. I have a question...
When I use musn't and when I use can't ? Thanks for help me!!


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## Zarcero

_*musn't*_ - prohibido hacerlo (pero a veces con permiso).
_*can't*_ - incapaz de hacerlo.


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## Agró

Solo una corrección: mus*t*n't (con 't', aunque no se pronuncie).


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## Zarcero

Agró said:


> Sólo una corrección: mus*t*n't...


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## gengo

Miinniie said:


> I have a question...
> when I use musn't and when I use can't ?



In American English we rarely, if ever, use mustn't.  It sounds very British.


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## Zarcero

gengo said:


> In American English we rarely, if ever, use mustn't.  It sounds very British.



I've heard it quite a bit in the mid-Atlantic states.  Almost never out west.


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## gengo

When it _is_ used in the US, it sounds snobbish.

You mustn't cry:  British
Don't cry:  American


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## spatula

gengo said:


> When it _is_ used in the US, it sounds snobbish.
> 
> You mustn't cry: British
> Don't cry: American


 
What if it's not a direct demand and, instead, advice - would you say 'shouldn't'?


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## cyberpedant

Although I can't think of any specific context in which one shouldn't use "mustn't" (or when one mustn't use "shouldn't," for that matter), perhaps a sentence or two would help us with the nuances.
Welcome to the forum, Miinniie.


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## gengo

spatula said:


> What if it's not a direct demand and, instead, advice - would you say 'shouldn't'?



No, shouldn't is a bit different, I think.  And, yes, we change the advice to a command.  I agree that some measure of nuance may be lost in this case, but that's the situation.  We just don't say it.  (I know that it was said above that it is used in some states, but I think I would hear it used on TV and in movies if that were the case.)

Furthermore, we don't use the positive "must" as often as the British do.

British:
-You must be brave.
American:
-Be brave.
-You've got to be brave.
etc.

I won't say that we never use must this way, but I hear it much more often in British speech than in American speech, in which it has a fairly high register.  It is therefore use in formal speeches and so forth, where it has the desired effect.


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## Zarcero

I think *gengo* is kinda right.  When I moved from L.A. to Maryland, *mustn't *was used more in the Northeast.  The further north I went, like college in New York, the more I heard it.  There is more "Britishness" on the Eastern Seaboard than there is in the rest of the US, in my opinion.


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## gengo

For the archive, I should point out that "must" is very much alive and well in the sense of "deber de + inf," for example.

-Who is that at the door?
-It must be the mailman.
Debe de ser el cartero /  Será el cartero.


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## spatula

Bandama said:


> I would say (in my experience as a non-native speaker) that even in British English, "must" is less and less used today. This is particularly the case with "mustn't", which it's hardly ever heard nowadays.
> 
> Do you British speakers agree?


 
Hmmm.  I'm not so sure Bandama.  In my experience it's very much alive and well in both its positive and negative forms.  It's a real eye-opener to learn that it's rather less so in the States; I had no idea.


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## Bandama

spatula said:


> Hmmm.  I'm not so sure Bandama.  In my experience it's very much alive and well in both its positive and negative forms.  It's a real eye-opener to learn that it's rather less so in the States; I had no idea.



In which situations dou you really say "mustn't"? Think of examples that don't sound a bit stilted, at least when talking to adults.


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## spatula

Bandama said:


> In which situations dou you really say "mustn't"? Think of examples that don't sound a bit stilted, at least when talking to adults.


 
_A. 'You mustn't (shouldn't) let him get to you, he's not worth it.'_
_B. 'You mustn't (can't) have heard her correctly, that's not what she said.'_
_C. 'You mustn't (can't) be doing it properly because doesn't look right.'_

I'm too close to it to see if there's pattern here - do you see one?  I've put what the alternative could be in brackets, but in each of these I'd both use and expect to hear 'mustn't' first and foremost in BE.


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## gengo

A is different from B and C here. What I wrote in post #13 above applies to  B and C, while A is related to what we were discussing above, in the sense of advice.

Here is how these would be said in standard American English.

_A. 'You shouldn't/can't let him get to you, he's not worth it.'_
_B. 'You must not have heard her correctly, that's not what she said.'_
_C. 'You must not be doing it properly because it doesn't look right.'_

We don't contract "must not" to mustn't, as a rule.


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## spatula

gengo said:


> A is different from B and C here. What I wrote in post #13 above applies to B and C, while A is related to what we were discussing above, in the sense of advice.


 
Different or not, they are all examples of how 'mustn't is used in BE.


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## mancunienne girl

I would add that although the abbreviation is often heard, it is seldom contracted in written language in the UK. Spoken language often differs from written language.


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## spatula

mancunienne girl said:


> I would add that although the abbreviation is often heard, it is seldom contracted in written language in the UK. Spoken language often differs from written language.


 
Just as well, given that it's such an ugly looking word .  Ah well, _mustn't grumble._


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## mancunienne girl

Bandama said:


> I would say (in my experience as a non-native speaker) that even in British English, "must" is less and less used today. This is particularly the case with "mustn't", which it's hardly ever heard nowadays.
> 
> Do you British speakers agree?


Yes, I certainly do. I would also say that "don't cry" is no more American than British. We are far more likely to say "don't cry" than "you mustn't cry", which sounds like something from an old weepy film set in the 40s....... so terribly old fashioned and formal....


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## DWO

At my (British) English Academy, they taught us the following:

you mustn't = no debes = "no debes hacer eso" (as in "puedes, pero no debes")
you can't = no puedes = "no puedes hacer eso"
you shouldn't = no deberías = "no deberías hacer eso"


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## lantern

I would only use "mustn't" in the sense of "*no deber de* + inf.":

He mustn't be at home; they mustn't have heard you; she mustn't be well, etc.

"Mustn't" with the meaning of "prohibido hacerlo" is not something you'd hear very often where I live. You might be regarded as "posh" if you spoke that way. I think when Americans talk about something sounding "British", they are often thinking of the stereotypical posh English accent (heard in TV programs and films), which is not how most people here talk.


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## mancunienne girl

gengo said:


> When it _is_ used in the US, it sounds snobbish.
> 
> You mustn't cry:  British
> Don't cry:  American



No. We tend to use the latter also in the UK.


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## lantern

Bandama said:


> I would say (in my experience as a non-native speaker) that even in British English, "must" is less and less used today. This is particularly the case with "mustn't", which it's hardly ever heard nowadays.
> 
> Do you British speakers agree?


Used in the way I've mentioned above, it sounds completely normal and is heard everywhere.


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## lantern

mancunienne girl said:


> Yes, I certainly do. I would also say that "don't cry" is no more American than British. We are far more likely to say "don't cry" than "you mustn't cry", which sounds like something from an old weepy film set in the 40s....... so terribly old fashioned and formal....


I agree. I don't think I've used "mustn't" in that way ever.


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## spatula

Well I don't think any BE speaker here has actually said that they *do* say _'you mustn't cry'_, so let's take it as read that this particular phrase isn't in use.  However, _'mustn't'_ in other situations such as those already suggested, is definitely in frequent use in BE.


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## Bandama

spatula said:


> _A. 'You mustn't (shouldn't) let him get to you, he's not worth it.'_
> _B. 'You mustn't (can't) have heard her correctly, that's not what she said.'_
> _C. 'You mustn't (can't) be doing it properly because doesn't look right.'_
> 
> I'm too close to it to see if there's pattern here - do you see one?  I've put what the alternative could be in brackets, but in each of these I'd both use and expect to hear 'mustn't' first and foremost in BE.



Hi.

What I meant was that I hardly ever hear "mustn't" *when it means prohibition*. Of course, it's a different thing when it works as a modal of probability expressing negative conclusion (examples B and C). 

Anyway, I'm not saying that it's not used at all (there are lots o set expressions with it like _mustn't grumble_), only that it seems to me that people tend to say more today "shouldn't" or "can't" (depending on the situation). My theory is that this probably happens because the sense of moral prohibition attached to "mustn't" is seen as something old-fashioned, only applicable to children.


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## *BamBina*

gengo said:


> No, shouldn't is a bit different, I think. And, yes, we change the advice to a command. I agree that some measure of nuance may be lost in this case, but that's the situation. We just don't say it. (I know that it was said above that it is used in some states, but I think I would hear it used on TV and in movies if that were the case.)
> 
> Furthermore, we don't use the positive "must" as often as the British do.
> 
> British:
> -You must be brave.
> American:
> -Be brave.
> -You've got to be brave.
> etc.
> 
> I won't say that we never use must this way, but I hear it much more often in British speech than in American speech, in which it has a fairly high register. It is therefore use in formal speeches and so forth, where it has the desired effect.


 
We use all of those forms in British English so I wouldn't say the last two are particularly American English, just that the first is used less in the States. I think 'must' is also quite formal in BE.

Bam


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## elprofe

toc said:


> Tienes razón, pero es mucho más común que se use con el sentido de suposición (p.ej. "John mustn't be at home" - "John no debe de estar en casa") que para denotar obligación/prohibición (que sí puede sonar un poquito old-fashioned, al menos para mí).
> 
> 
> A mí también.



?¿?¿?¿ A lo mejor os suena natural, pero "John mustn't be at home" no es correcto. _Mustn't_ sólo indica prohibición, y no hay nadie ni nada que le prohíba a John estar en su casa.
Esa oración debería ser: John can't be at home (because I have just seen him at the supermarket)
_Must_ en afirmativa sí que puede indicar suposición casi segura:
- It's 10am, John must be at the office. --- > correcto
- The lights are turned off, he must have left.----> correcto
- The lights are turned off, he can't be at home.---> correcto
- The lights are turned off, he mustn't be at home ---> Incorrecto


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## Vidar1984

toc said:


> Tienes razón, pero es mucho más común que se use con el sentido de suposición (p.ej. "John mustn't be at home" - "John no debe de estar en casa") que para denotar obligación/prohibición (que sí puede sonar un poquito old-fashioned, al menos para mí).
> 
> 
> A mí también.


 
This is also entering into a difference between US English and UK English.  In the US we would never say "John mustn't be at home."  We would simply never say it.


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## frida-nc

This is also entering into a difference between US English and UK English. In the US we would never say "John mustn't be at home." We would simply never say it.

A very late addition to what Vidar notes:
We could very well say, in the US: *John must not be home.  *[Parece que no está.]  It's the contraction we don't use, at least in this sense.  In point of fact, "you mustn't do that" (prohibition) is far more recognizable to me than "John mustn't be home."


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