Questions about the Plus-que-parfait
Q: Why is it Si j'avais su ... and NOT Si j'aurais su ...?
After the word Si, you can use the present, the imperfect or the future. However, it cannot be followed by the conditional or the past conditional. It is true that English uses the structure "would have" , e.g.: "If I would have known", but this can't be a conditional in French. Rather, you should use the plus-que-parfait.
Often, you will find the past conditional used after an instance of the plus-que-parfait, e.g.: Si je l'avais su, je ne l'aurais pas fait.