must have to do sth

[joham]

I read these two sentences in Hewings' ADVANCED GRAMMAR IN USE (2005 edition) unit 18:

I can't start the computer. You must have to know a password.
John wasn't at home when I went round. He must have had to go out unexpectedly.

This is the first time I've read sentences with 'must' used together with 'have to' and 'have had to'. I was surprised how these two modal verbs with the same meaning could be used side by side. Is it standard English?

Thank you very much.

 

[riverkid]

I read these two sentences in Hewings' ADVANCED GRAMMAR IN USE (2005 edition) unit 18:

I can't start the computer. You must have to know a password.
John wasn't at home when I went round. He must have had to go out unexpectedly.

This is the first time I've read sentences with 'must' used together with 'have to' and 'have had to'. I was surprised how these two modal verbs with the same meaning could be used side by side. Is it standard English?

Thank you very much.

Sure, it's standard, Joham. This is epistemic must, denoting that the speaker is slightly less than 100% certain. If the speaker had been 100% certain, there would be no must.

 

[AstroNox]

This is the first time I'm seeing this use too. I don't think it's frequently used right?

 

[riverkid]

This is the first time I'm seeing this use too. I don't think it's frequently used right?

Comparing it to a straight 'have to', no, it isn't all that common but I think [I could be wrong] that we tend to make more 100% statements of fact in English than qualified 100% statements.


Results 1 - 10 of about 1,730,000 English pages for "must have to".

Results 1 - 10 of about 53,700,000 English pages for "have to".

 

[AstroNox]

I'd guess that such 100% assumptions make life easier. Besides, in laypeople's conversational English most would probably disregard the implication of "must".