Breakdown of Esperávamos o comboio quando vimos o acidente.
o comboio
the train
quando
when
ver
to see
esperar
to wait
Questions & Answers about Esperávamos o comboio quando vimos o acidente.
Why do we use two different past tenses in this sentence?
This is a classic example of how the two past tenses work together. Esperávamos is in the Pretérito Imperfeito because it sets the scene with an ongoing background action ("we were waiting"). Vimos is in the Pretérito Perfeito Simples because it is a sudden, completed action ("we saw") that happened while we were waiting.
In English we say "waiting for", so why isn't there a word for "for" after esperávamos?
The Portuguese verb esperar directly connects to the thing you are waiting for. You just say esperávamos o comboio (literally "we awaited the train") without needing an extra preposition to translate "for".
Both verbs end in -mos. Is it mandatory to drop the word nós (we) from the beginning of the sentence?
It is not mandatory, but it is the most natural way to speak. Because both esperávamos and vimos end in -mos, it is immediately obvious that "we" are doing the action, making the word nós unnecessary.
Why does esperávamos have an accent mark?
For regular -ar verbs in the Pretérito Imperfeito, the "we" form always ends in -ávamos. The acute accent mark is required to show that the pronunciation stress falls on that "a" rather than on the second-to-last syllable.