Breakdown of Não fossem os teus reflexos, o desastre teria acontecido.
ser
to be
não
not / no
ter
to have
teu
your (informal, m/f/pl: teu, tua, teus, tuas)
Questions & Answers about Não fossem os teus reflexos, o desastre teria acontecido.
Why do we skip the word se (if) at the beginning of the sentence?
Why is the verb plural (fossem) when the main subject of the sentence (o desastre) is singular?
What tense is fossem and why do we need it here?
It is the imperfect subjunctive (imperfeito do conjuntivo). This tense is required because the clause describes an unreal or contrary-to-fact situation. In reality, you did have good reflexes, so we must use the subjunctive to imagine the opposite scenario.
Could I say tinha acontecido instead of teria acontecido in the second half?
Yes, in everyday spoken Portuguese, it is very common to replace the conditional perfect (teria acontecido) with the pluperfect indicative (tinha acontecido) to mean 'would have happened'. However, because the Não fossem... structure is slightly elevated, the conditional perfect used here is the best stylistic match.