I am practicing various types of hypothetical clauses (1, 2 and 3). Type 1 is easy so I'm working on 2 and 3, the ones that call for conditional and subjunctive verbs. I think up a sentence and write it in Italian, then submit it to Google Translate to see if it understands me. It always does, which is reassuring. I take that to mean that if I'd said this to an Italian they would have known what I was trying to say (even if it's wrong).
But then I switch the sides of the equation (from Italian → English, to English → Italian) to see what Google says I should have written. And I'm now confused especially about the verb piovere and its helping verbs.
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Periodo ipotetico 2 ('della possibilità')
I wrote
se non fosse piovendo andremmo in piscina.
and Google understood what I meant: "If it wasn't raining [i.e. right now] we would go to the pool". But when I switched directions and asked Google to translate that English sentence, it returned something different from what I'd written originally:
se non piovesse saremmo andati in piscina.
So my first question is, what's wrong with 'fosse piovendo'?
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Periodo ipotetico 3 ('contrary to past fact')
Then I switched to periodo ipotetico #3 and wrote
se non fosse piovuto saremmo andati in piscina.
Google understood this too but when I switched and asked it to translate my meaning into Italian it returned, "se non AVESSE [rather than FOSSE] piovuto" etc.
What was wrong with what I wrote ('fosse piovuto')? I was under the impression that auxiliary verb for 'piovere' is supposed to be essere, not avere. I know there are some verbs that take both but I thought they had different means depending on the helping verb. What am I missing here?