I'd like to
clean the sky clear the air about ... I think that's what you mean, although even if you correct the idiom, the use of it here is still inappropriate. "clear the air" is what you usually do after a heated argument or disagreement.
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could can substitute for
would without changing the numbering system of the conditionals.
If ... [past] ..., could ... Second conditional.
If ... had ..., could have ... Third conditional.
If ... [past] ..., could have ... Mixed.
If ... had ..., could ... Mixed.
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Frankly, I find the following just a bit anomalous.
He could have been Prime Minister now if he had not decided to leave politics. [Third, not Mixed, Conditional]
been seems to mean
become here, and, in my opinion, it doesn't go with
now. To resolve this contradiction, I assign this meaning:
He
could have become Prime Minister (in the past) [and if he had become Prime Minister
then, he
would (still)
be Prime Minister
now] if he had not decided to leave politics. [The implicit conditional is mixed.]
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I don't understand what you intended to convey by reconstructing this without
have:
He could be Prime Minister now =~ He [may / might] be PM now =~ Maybe he is PM now. (So I'm going to ignore it!)
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Here's a famous example of the
could have been structure:
CJ