What is the standard formula for making a counterfactual conditional sentence that talks about the past? That is, English conditionals that have this pattern: "If ..... had ..... , ..... would have ...... "
I have checked these similar questions asked previously, but the answers don't seem to match up well (or at least I fail to see the common pattern):
(1) here, the working example is "安ければ買った". Non-past conditional in first clause + plain past second clause.
(2) here, the working example is "あのとき右に曲がっていれば(or いたら)、どうなっていた（の）だろう". Conditional of -te iru form in 1st clause + past of -te iru form in 2nd clause.
(3) here, the working example is "もしお金を持っていたら、食べ物を買っていた" or "もしお金があったら、食べ物を買っていた". Conditional of -te iru form in 1st clause + past of -te iru form in 2nd clause. And the alternative sentence is non-past conditional in 1st clause + past of -te iru form in 2nd clause.
The answers in the above pages made me confused because I don't quite get whether -te iru form is necesssary or preferred when making conditionals of this kind. And whether it is necessary or preferred in both parts of the sentence (first and second clause).
I also tried some examples of my own with online translators:
"If I had eaten those mushrooms, I would have fallen sick."
Both Google Translate and deepL give this: あのキノコを食べていたら病気になっていた (でしょう/だろう)
"If it had been dark, I would not have been able to see."
Google Translate: 暗かったら見えなかったでしょう。
The best rule I can build out of these is:
-te iru conditional + -te iru past is preferred in these kind of conditionals; except for when the verb cannot take -te iru form (like aru) or when the clause is an adjective or noun sentence.
Though I still am at a loss about whether -te iru past is preferred for second clause or not. Or whether using plain past vs. -te iru past in the second clause creates two sentences with different meanings.
It'd be great if someone could correct or fine-tune this rule (or perhaps present the standard rule for counterfactual past conditionals, if there is one).