When you come to London again, you ... come and see us

[Grablevskij]

English Grammar in Use by Rymond Murphy. Second edition
Unit 31 (Must and have to).

Please, have a look at the screenshots (3 pieces).

When you come to London again, you ... come and see us.

The key gives: must or have to.

I suppose, have to is impossible here. Have to is used when you are forced to do something by the situation. So, it is impersonal. But must comes from a person. I say it is necessary that you must come and see us. And this corresponds to the explanation in the theoretical part (the example "You must meet her").

Could you speculate on the subject of whether have to is possible or impossible here.

 

[5jj]

Not everybody uses must and have to in the way Murphy describes, even in BrE.

Note how I have used italics to differentiate the words I am writing about from the message. You used bold font, which is acceptable, but you did not use it consistently.

 

[5jj]

I would probably use must, in your sentence, but I don't consider have to incorrect.

 

[jutfrank]

Before looking at any options, I naturally and unthinkingly filled the gap with have to.

This is a case of have to for urging somebody to do something.

 

[5jj]

Before looking at any options, I naturally and unthinkingly filled the gap with have to.

Whereas I naturally filled it with must.

This is a case of have to for urging somebody to do something.

For which some speakers of BrE use must, emphasisd in speech.

 

[jutfrank]

Whereas I naturally filled it with must.
For which some speakers of BrE use must, emphasisd in speech.

Right. I'm pretty sure (and I assume from the OP) Murphy fails to mention that both forms are equally effective for this use.

Preference depends largely on the speaker. For me, must sounds frightfully old-fashioned and terribly middle-class. I don't think American speakers would use it, either.

 

[5jj]

frightfully old-fashioned and terribly middle-class.

Got you at last! 'jutfrank' is one of my offspring, who have used that and similar expressions of me countless times.

 

[jutfrank]

Oh, Mr 5jj, you simply must join us at the villa next time you're in Nairobi. I'll have Watkins make up the guestroom.

-D)

 

[5jj]

Tiffin at three?