Breakdown of Foi impossível manter a casa limpa sem vocês contribuírem.
ser
to be
a casa
the house
vocês
you (pl)
limpo
clean
Questions & Answers about Foi impossível manter a casa limpa sem vocês contribuírem.
Why do we use the conjugated verb contribuírem instead of the normal infinitive contribuir?
Because the subject changes. The first part of the sentence is impersonal (foi impossível). However, the action of contributing has a specific subject (vocês). After the preposition sem, we use the personal infinitive so we can add the -em ending to show exactly who is (or isn't) doing the action.
Could I use the subjunctive here and say sem que vocês contribuíssem?
Yes, that is grammatically correct and means the exact same thing. However, using sem followed by a personal infinitive is often preferred by native speakers because it is more concise and lets you avoid tricky subjunctive conjugations altogether.
Why is manter in the unconjugated infinitive if the sentence is about the past?
The phrase manter a casa limpa acts as the subject of the sentence (literally: 'To keep the house clean was impossible'). When an action functions as a general concept like this, it stays in the impersonal infinitive. The past time frame is already set by the verb foi.
Why does contribuírem have an accent mark on the i, when the base verb contribuir doesn't?