Is "could have"/"would have" ever used to talk about future events that can't happen anymore?
Let's say your friend is going traveling tomorrow, as a result of which, you can't meet them tomorrow. Now, if such a conversation takes place between you two, is it okay to use could have here:
Friend - I really wanted to meet you.
You - We could've met tomorrow. Maybe we'll hang out when you get back.
Is the use of could've fine here?
If the idea has been squashed, then pondering an opportunity that will be lost is the same as reflecting afterwards, so "We could have met up tomorrow" fits.
In Australia 'couldabeen champions' is a radio show which ran four decades - speculating on failure.
Is "could have"/"would have" ever used to talk about future events that can't happen anymore?
Yes.
Suppose that a few days ago you and I talked about the idea of meeting for lunch. Since then, your travel arrangements have changed, so we can no longer meet. I can say:
It's sad that your arrangements have changed. We could've met for lunch tomorrow.
In effect, this is the same as We can no longer meet tomorrow.
Note also that tomorrow could be replaced by today or yesterday. This is because could here has the sense of (in)ability. We were able to, but no longer. And I can apply that inability to any event, past/present/future. In a week, I can look back and say, I'm still sad, because we could've met last Wednesday.
Would've broadly works the same way, except that here it has a slightly different meaning. We would've met tomorrow implies that we had more definite arrangements to meet, and they had to be cancelled. But otherwise, would've has the same structure and can be used for past/present/future contexts.
OP's query:
We could've met tomorrow. Maybe we'll hang out when you get back.
Is the use of could've fine here?
The use of could've is fine in: We could've met tomorrow. This sentence is a condensed third conditional containing only the main clause.
Let's look at the structure of the second and third conditionals.
Ref. learnenglish.britishcouncil.org
Second Conditional structure is usually:
if + past simple >> + would + infinitive..
In Third Conditional sentences, the structure is usually:
If + past perfect >> would have + past participle.
OP's sentence can be rewritten in the following manner:
'1. If you weren't traveling, we could've met tomorrow.
In this sentence the if clause is a hypothetical or an impossible clause (because the friend has already decided to travel). So it is a mixed conditional. "If clause" is Second Conditional and main clause is third conditional.
Now if we rewrite the sentence in this manner:
'2. If you had not decided to travel, we could've met tomorrow..
Now the if clause is in Past Perfect - the friend had already decided to travel and the decision cannot be changed.
The third conditional often expresses regret about past actions.
These past tense modals are useful for expressing your present feelings about a past decision (or other action).
In the post, the decision to go travelling was made in the past, and hence this past tense modal could have is appropriate for certain constructions: We could've been able to meet tomorrow.
We could've met tomorrow.
doesn't seem right. Could've met should refer to time past.
