I was wondering if you could provide clarification in the difference between mitzvah habah biaverah (which is assur) and mitzvah doche lo saaseh (which is mutar). Please clarify when we apply which, and why.
Yehoash Orange
Brooklyn NY
The Torah Temimah in Bechukosai (218) poses your problem (almost word for word). This is what he says:
Where it is impossible to fulfill the Asei without negating the Lo Sa'aseh (such as a Gerushah or a Chalutzah who fall to Yibum to a Kohen Hedyot or Kil'ayim be'Tzitzis [attaching Techeiles - dark-blue woolen Tzitzis - on to a linen garment]), we will apply the principle 'Asei Docheh Lo Sa'aseh' (because the La'av falls away before the Asei).
But where the Mitzvah can be fulfilled be'Heter as well, such as Matzah of Tevel, or a stolen Lulav or one from an Asheirah, the principle 'Mitzvah ha'Ba'ah ba'Aveirah' applies, since the Mitzvah can theoretically be fulfilled with other Matzah and another Lulav (even if he does not have any).
R. Eliezer Chrysler