The Rambam writes (Chameitz u’Matzah 1:3) that if one purchases chameitz on Pesach, one would receive malkos. The meforshim address themselves to two difficulties in the Rambam: 1) Bal yera’eh u’bal yimatzeih can be violated simply by owning chameitz, a completely passive state; why are these lavim not categorized as lavim she’ain bahem ma’aseh for which there is no malkos? 2) The mitzvas aseh of destroying chameitz *tashbisu) corrects the lav of owning chamietz. Why are these lavim not categorized as nitak l’aseh for which there is no malkos?
The first problem can be dismissed if we assume the Rambam held (as do other Rishonim) that whether a lav is classified as ain bo ma’aseh is not determined on a categorical basis by the way a lav is normally violated, but is determined on a case by case basis based on whether the person took action or not.
The second problem brings us back to the chakira of the Minchas Chinuch (discussed last week). A lav hanitak l’aseh is a lav which the Torah provides corrective action for. The Minchas Chinuch and R’ Chaim Brisker explain that the Rambam held like Rashi, that the mitzvah of tashbisu is defined not the act of destroying chameitz, but the state of not owning chameitz. Since the mitzvas aseh is fulfilled passively by not possessing chameitz and does not not involve a specific corrective action, the lav is not categorized as a lav hanitak l’aseh.