Everyday Grammar: Could Have, Would Have

COULD HAVE
means that something was possible in the past, but it did not happen.
“I could have travelled the world, but I never got a pssport.”
To from the negative, just add not betweend could and have.
It means that something was impossible in the past.
“I could not have travelled the world, because I never got a pssport.”

WOULD HAVE
is a bit more complicated since it has two common meanings.
But we will only talk about the one that shows how you wanted to do something in the past, but you could not.
I would have A, but I had to B.
“I would have called but I had to work.”
The structure both modals is easy to remember.
could/would + have + past participle verb
Use have for all pronouns. Never use has or had to from a past modal.
use COULD HAVE when something did not happen.
use WOULD HAVE when something could not happen.