"Somebody had opened the window" should also be accepted as a valid translation of the sentence above.
Are there different ways to express the pluperfect? i.e. this versus "Alguém tinha aberto a janela"?
Yes, I was wondering that - it certainly looks like a different auxiliary verb used to make that compound tense
I'm not getting this. Shouldn't the translation be more like: "someone used to open the window" or "someone was opening the window"
This is the Futuro do Pretérito (and only havia in past imperfect, aberto is past participle), right? It could be used in the conditional perfect, like this (?): Se não tudo mundo tivesse ido para a festa ontem, alguém havia aberto a janela.
Is "Alguém havia aberto a janela." Futuro do Pretérito, where only havia is in the past imperfect, and aberto is the past participle?
Can I use the phrase in a sentence with the conditional perfect like this?:
Se não tudo mundo tivesse ido para a festa ontem, alguém havia aberto a janela.
I sincerely don't remember the name of the times haha, but "Se não tudo mundo tivesse ido para a festa ontem, alguém havia aberto a janela." sounds a little strange, I would rather say: "Se não tivesse todo mundo ido para a festa ontem, alguém teria aberto a janela".