[Grammar] mustn't have

[silentknight]

In one of the threads here I have read that mustn't have + perfect infinitive exists and can be freely used. As an English teacher I have always taught that it doesn't exist. Never have I met this structure in any descriptive grammar books. What is the truth about it?

Thank you in advance.

 

[mara_ce]

Hi silentknight,

I took part in this thread because I had never heard or seen the use of that structure before.
https://www.usingenglish.com/forum/teaching-english/116291-couldnt-have-vs-mustnt-have.html
I asked some teachers here and all of them reacted in the same way. I wonder what would happen if I decided to write mustn´t have been instead of can´t have been to show certainty about something in an international exam. I don´t think it would be accepted.

I´ve found this use in another grammar book:

mustn´t have = necessity in the past
e.g.: You mustn´t have had any driving convictions or you won´t get the job.

 

[Raymott]

Hi silentknight,

I took part in this thread because I had never heard or seen the use of that structure before.
https://www.usingenglish.com/forum/teaching-english/116291-couldnt-have-vs-mustnt-have.html
I asked some teachers here and all of them reacted in the same way. I wonder what would happen if I decided to write mustn´t have been instead of can´t have been to show certainty about something in an international exam. I don´t think it would be accepted.
It might not be accepted if the exam is marked by a non-native speaker, if it is as unknown as you say.
I'd pass you, if that's any consolation.

I´ve found this use in another grammar book:

mustn´t have = necessity in the past
e.g.: You mustn´t have had any driving convictions or you won´t get the job.
Yes, that's a different meaning. Less common than the other one.

R.