She must have made a mistake. It couldn't be true.

[shootingstar]

There are the main clauses:

She must have made a mistake. It couldn't be true.

Does the clause "It couldn't be true" have any past tense meaning in this context? If not, what tense does this clause have? What modality, feeling or mood does this clause express?

 

[jutfrank]

I suggest that instead of making up artificial sentences and asking us what you mean, find a real example of real language in use, and we can look at it together, if it's good enough.

 

[shootingstar]

Sorry. These clauses aren't made up and they aren't artificial. They are mentioned in my grammar book actually and I'm afraid I don't understand their meaning.

 

[emsr2d2]

Sorry. These clauses aren't made up and they aren't artificial. They are mentioned in my grammar book actually and I'm afraid I don't understand their meaning.

In that case, you must cite the source in full. Please give us the title of the book and the name(s) of the author(s).
We cannot help you until you fulfil this legal requirement.

 

[jutfrank]

Also post a screenshot or link to the page in question. If we know why the writer wrote that particular sentence, then we'll know what it means.

 

[shootingstar]

In that case, you must cite the source in full. Please give us the title of the book and the name(s) of the author(s).
We cannot help you until you fulfil this legal requirement.

It's the grammar book "English Grammar Today", Cambridge University Press, 2011.

 

[shootingstar]

Meanwhile the problem has been solved. "Could" is past simple , and "couldn't" expresses strong negative possibility in this context.