They couldn't be or they couldn't have been at home

rcjm

Member
Spanish
Hi everyone:
Which sentence is correct?
a) I was at your parents' last night but the lights were off. They couldn't have been at home.

b) I was at your parents' last night but the lights were off. They couldn't be at home.

Personally, I prefer a) but is b) also correct?
It often happens with modals that some native speakers seem to go for an option which sounds awkward to me.
Of course, It could be paraphrased with "must have been out". Also, I understand some native speakers of AmE use "mustn't" (rather than "couldn't") for negative deductions, so a paraphase along the lines of c) below may be common in AmE:
c) I was at your parents' last night but the lights were off. They mustn't have been at home.
So, is a) better than b)? Is c) also correct in American English?

Thanks in advance.
 
  • gengo

    Senior Member
    American English
    a) I was at your parents' last night but the lights were off. They couldn't have been at home.
    b) I was at your parents' last night but the lights were off. They couldn't be at home.

    Personally, I prefer a) but is b) also correct?

    No, only a) is correct, but even a) sounds a bit odd. I would say:

    I went by your parents' house last night but the lights were off. They must not have been (at) home.

    It's best to use "must" when referring to supposition. Using "couldn't" means that it was impossible for them to be home, which is clearly not true, since they might have been in bed.
     

    Bevj

    Allegra Moderata (Sp/Eng, Cat)
    English (U.K.)
    In BrE I would have no problem with saying 'They couldn't have been at home'. Both 'couldn't' and 'mustn't' in this context suggest to me that the speaker is certain that the people were out.
    Whether they were in bed or not is an unknown issue which he doesn't appear to have taken into account.

    (They must have been out is a much better solution.)
     

    mylam

    Senior Member
    United States English
    (b) is incorrect, since you're talking about last night, but "couldn't be" is present tense.
     

    S.V.

    Senior Member
    Español, México
    Also along the lines of this example: te debiste de oler a ti mismo (→you must have smelled yourself); no debían de estar en casa (→must not have been at home).
     
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