'could not + have + past participle'

[riceball72]

Hi

Was wondering if anyone has any extra advice or comments on this structure:

could not + have + past participle

my grammar books say basically that it is used to express something that could not have been possible in the past.

I understand this, but when this is used in a sentence it also gives me the feeling of 'disbelief' or 'impossibilty'...

He couldn't have been a porpoise!
He couldn't have eaten all the cheese!

How would you describe this structure and use of it?
Anything different to what the grammar books say?

Smiles
Riceball

[pablo_ivher]

I would say that something that could not have been possible in the past is something with disbelief of impossibility, you are in the correct thinking of what function the past perfect has

hope this helps.