'must' for probability

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Explorer

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Is it correct to use 'must' for expressing probability in sentences like

'He must return, he's forgotten his umbrella.' (He will probably return, he's forgotten his umbrella)
'He's trained much, he must win the game'. (He's trained much, he will probably win the game)
 

abaka

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"Must" is indeed sometimes used to mark probability in certain informal contexts. Examples:

Given how well the Netherlands has been playing, they must surely win the championship this year.

He has many umbrellas. He must have a hard time picking one.

But it's not a good usage if there is the least possibility of confusion with the usual "must" of obligation or necessity. Therefore your second sentence is perhaps acceptable, although it should be avoided in formal writing. Your first sentence is very questionable, I think.
 

charliedeut

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abaka;896754 [I said:
Given how well the Netherlands has been playing, they must surely win the championship this year.[/I]

Which championship are you talking about? Surely not the Euro2012, they could have hardly done worse there :shock: ;-)
 

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5jj

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The use of 'must' to indicate logical certainty is not particularly informal.

It is not generally used if there is a possibility of ambiguity. When it is clear that the present moment is being spoken of, then there is no problem; 'must's uggesting obligation almost always applies to something that must be done after the moment of speaking.

'He must return, he's forgotten his umbrella.' (not for logical certainty)
'He must be very wet; he's forgotten his umrella.' (fine for logical certainty)
'They must win tomorrow, or I'll lose my bet.' (not for logical certainty)
'They must win tomorrow after all the money they've spent on new players'. (possibly ambiguous)
 

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One question more in this topic.
The sense of which expression of the two ones placed below is closer to the sense of 'He must be very wet...'
'He is certainly very wet...'
'He is probably very wet...'
?
 

5jj

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It's probably closer to 'certainly'. Will suggests more absolute certainty than must, which suggests a logically deduced certainty; that is stronger than probability.
 

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Thank you very much for your answer.

Please check the following examples whether they contain any ambiguity. In all of the sentences the speaker expresses certainty with respect to future events.

'His car is moving 10 Km/h faster, he must come up with Jon in an hour.'
'She dresses brightly, he must notice her right after he comes the hall.'
'She understands that her arguments are weak, she must change your opinion.'
'He has a strong influence on the community, they must accept his proposal after the first reading.'
'- I am afraid this problem may upset the plans. - Don't wory, Eddy is an inventive guy, he must arrive at a solution quickly.'
 

birdeen's call

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It's probably closer to 'certainly'. Will suggests more absolute certainty than must, which suggests a logically deduced certainty; that is stronger than probability.

Perhaps "logical deduction" rather than "logically deduced certainty"? I'm not sure it always expresses certainty. I actually think it can be found in sentences expressing uncertainty (without any irony).

I don't get it. With all the balloons and the funny hats and stuff, it must have been a lot of fun, right? How come then my son won't speak to me? He's acting like I've done something wrong.

Here, the speaker is deducing something, but they are not certain their deduction is correct. They see there's a problem they don't understand, and they accept that their may be a flaw in their deduction.
 

5jj

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Perhaps "logical deduction" rather than "logically deduced certainty"? I'm not sure it always expresses certainty. I actually think it can be found in sentences expressing uncertainty (without any irony).

I don't get it. With all the balloons and the funny hats and stuff, it must have been a lot of fun, right? How come then my son won't speak to me? He's acting like I've done something wrong.

Here, the speaker is deducing something, but they are not certain their deduction is correct. They see there's a problem they don't understand, and they accept that their may be a flaw in their deduction.
I see your point, but am not totally convinced. I think the speaker is very nearly certain (not absolutely certain - that's will). Given that near-certainty, they cannot understand why their son is unhappy. There is not necessarily a flaw in their deduction. The party may have been fun for everybody except their son. If that's the case, they want to know why.

One point about logically deduced certainty (or even absolute certainty) is that it is certainty, not fact, expressed by the speaker:

A: You co-authored a book with Arthur Nicholls once, didn't you?

B1: Yes, that was in 1969. (I remember that clearly. It was the year my daughter was born. My wife did some proof-reading in the maternity ward! Apart from that, I have shamelessly cited the book whenever I can, so 1969 is fixed in my mind.)
B2: Yes. That will have been in 1969. ( It was the last year we shared a flat together, and I am certain that that was 1969)
B3: Yes That must have been in 1969. (That was while we still sharing a flat. I left the following year to get married. I got married in 1970, so I am now certain, after logical deduction, that we wrote the book in 1969).

I readily concede that there is not a clear-cut difference between will have and must have in my examples, and that must have is possible for B2 and will have is not impossible for B3. My point is that must have is, in my opinion, closer to the idea of certainty than it is to the idea of probability and that, for each individual speaker, will have is more absolutely certain than must have.
 

birdeen's call

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I agree about your examples, but I think mine is less clear. I agree that your reading of it is possible -- I didn't think of it when I made it up. I understand you read the "right" as a kind of rhetorical question. But I think it could also be a genuine expression of doubt or even soliciting confirmation. I believe intonation and facial expression matter here. Imagine that the person is saying the "right" with a rising intonation and with a facial expression similar to this. (It's not exactly the expression I wanted, but I can't describe it, and that's the closest I've been able to find.) Perhaps a "surely" instead of the "right" would be more convincing, but it can also be pronounced in different ways denoting different modalities in my opinion. Even without the "right" or "surely", I believe uncertainty could be conveyed by the intonation of "must", perhaps accompanied with this gesture and the facial expression.
 

5jj

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I agree about your examples, but I think mine is less clear. I agree that your reading of it is possible -- [etc]
I cannot disagree with anything you say - and your excellent command of English makes it possible for you to understand that that does not necessarily mean that I agree with everything you say. ;-).
(It's not exactly the expression I wanted, but I can't describe it, and that's the closest I've been able to find.)
I understand exactly (please accept that I did not mean to sound smug/arrogant there). After more than forty years of work, I feel that I have a fair understanding of how tense and aspect are used in English, but I still, like Palmer and many others, find modals 'messy' (Modality and the English Modals (Palmer, 1979, p.39)).
I believe intonation and facial expression matter here.
I agree. That is one of the things that makes abstract discussion of the words so difficult.
 

5jj

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For the 1st one, I would use ‘He will return' or ' He has to return'.
for the 2nd, I would say ' he will win the game'.
I cannot tell why and I am not a native speaker~ ;-)
I realise that you are just trying to build up posts so that you can post a link to your survey, but please don't give answers if you have no justification for them.
 

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1. Is it correct to use the circumtances of time in 'he must have done that yesterday'?

2. Can 'he must visit them every day' express the idea 'he probably visit them every day'?


Thank you in advance.
 

Tdol

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1 Yes
2 The meaning to me is more like I am sure that he visits them...
 
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5jj

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1. Is it correct to use the circumstances of time in 'he must have done that yesterday'?
Sorry, but I don't understand your question. He must have done that yesterday is fine
2. Can 'he must visit them every day' express the idea 'he probably visits them every day'?
It can.
 

Jaskin

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hi,
Please note I'm not a native speaker nor a teacher;
I agree about your examples, but I think mine is less clear. I agree that your reading of it is possible -- I didn't think of it when I made it up. I understand you read the "right" as a kind of rhetorical question. But I think it could also be a genuine expression of doubt or even soliciting confirmation. I believe intonation and facial expression matter here. Imagine that the person is saying the "right" with a rising intonation and with a facial expression similar to this. (It's not exactly the expression I wanted, but I can't describe it, and that's the closest I've been able to find.) Perhaps a "surely" instead of the "right" would be more convincing, but it can also be pronounced in different ways denoting different modalities in my opinion. Even without the "right" or "surely", I believe uncertainty could be conveyed by the intonation of "must", perhaps accompanied with this gesture and the facial expression.

No disrespect but I really can't imagine a native English speaker saying "right" or "surely" or "mustn't it" with raising intonation. I think it might be your polish speaking ;-), as for uncertainty I personally would go for "can't". I really can't imagine myself using must for uncertainty.

I don't get it. With all the balloons and the funny hats and stuff, it must have been a lot of fun, right? How come then my son won't speak to me? He's acting like I've done something wrong

I would consider that the "must" expresses the speaker perception of the situation "I strongly believe that it was a lot of fun". As for me, the doubt arises from confrontation with their sons reaction and it's marked by the question tag "really?" and "I don't get it" not by "must" on its own.

I just realised that I'm unable to define necessity, obligation and expectation without using the word "must" - perhaps that's why it's so difficult to discuss the modality of that word.

cheers
 

Tdol

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I agree with Birdeen's Call- a native speaker could IMO use a rising intonation for "doubt or even soliciting confirmation".
 

Jaskin

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I agree with Birdeen's Call- a native speaker could IMO use a rising intonation for "doubt or even soliciting confirmation".

:-|:cry:
so countless hours spent learning to drop the intonation when using question tags can go down the drain.
Raising intonation is characteristic of Polish equivalent of question tags: prawda? nieprawdaż? Whereas I was corrected on countless occasion to drop the intonation when using question tags in English.

ps. I'm sorry for getting a bit off topic in my defence
 

Tdol

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Question tags can go up or down, depending on the meaning, which can range from confirmation through surprise to and genuine question,etc.
 
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