At the end of this week’s parshah, the Torah presents the mitzvah of tefillin. It states that we must guard this commandment from year to year. The Mechilta comments that these words indicate that a person must check his tefillin every 12 years.
The Mishkenos Yaakov derives from this halacha that we must also check the lungs of every animal that we shecht. We don’t check the lungs because we assume they are treif. In fact, the opposite is true. Just like we don’t assume tefillin are pasul after 12 years (if we did, then we wouldn’t need the Torah to tell us to check them), so too we don’t assume most lungs are treif. We check them nonetheless, though, because some might be.
The Meshech Chachmah takes issue with the Mishkenos Yaakov’s comparison. Wearing tefillin is a mitzvas asei, and eating treif is a mitzvas lo sasei. The Meshech Chachmah explains that when a person violates a lo sasei through no fault of his own (oneis), he isn’t held liable. Why? Because a lo sasei requires us to obey the wishes of Hashem and to refrain from doing what He commanded us not to do. If a person violates a lo sasei through no fault of his own, he isn’t held accountable since he didn’t intend to disobey.
A mitzvas asei, however, is different. A mitzvas asei requires, not refraining from acting, but acting. And if a person can take steps to perform the mitzvah, he should do so (even if he won’t be held accountable for not performing it due to circumstances beyond his control).
Therefore, it is no surprise that the Torah requires a person to check his tefillin every 12 years. True, probability (rov) tells us that the tefillin are most probably kosher, but there is no need to rely on this probability. A person can simply check his tefillin to make sure that he is fulfilling this mitzvah. But tefillin are a mitzvas asei. Eating treif is a lo sasei.It’s possible (based on the distinction we outlined above) that while we may not rely on probability for a mitzvas asei, we may do so for a mitzvas lo sasei.
This distinction is, in fact, how Achronim answer the question that Rishonim ask on the Rambam’s position that a safek d’Oraisa is permitted m’d’Oraisa (although it still is prohibited m’d’Rabanan) in light of a sugya in the Gemara (Chullin 11a). This sugya searches for a source in the Torah that we may follow probability (ruba l’lesa kaman – a majority of natural tendencies or behaviors). It suggests that the Korban Pesach is such a source. How so? Because we may eat a Korban Pesach even though it is impossible to check its head for any sign of treifos. (It’s impossible because the Torah commands us not to break any bonein the Korban Pesach.)The reason we may eat it is because the Torah allows us to rely on the probability that most animals are not treif.
This Gemara, however, is problematic according to the Rambam. He maintains that safek d’Oraisa is permitted m’d’Oraisa. If so, the Gemara’s source for relying on probability is a bad one. According to the Rambam, the reason a person may eat a Korban Pesach without checking its head for broken bones is because safek d’Oraisa is permitted m’d’Oraisa. It has nothing to do with probability. How, then, does the Rambam make sense of this Gemara?
The Chavas Da’as (Yorah Deah, pesicha to siman 110) answers that the Rambam only maintains that a safek d’Oraisa is permitted m’d’Oraisa regarding mitzvas lo sasei. However, regarding a mitzvas asei, if there is a doubt whether a person has fulfilled the mitzvah, he should ensure to remove any doubt since if it turns out that he did not fulfill the mitzvah properly he will not receive credit for performing it.
Therefore, regarding the mitzvah of Korban Pesach, the Rambam would not rule that safek d’Oraisa is permitted m’d’Oraisa. Thus, the Gemara is able to use the Korban Pesach to prove that we may rely on probability.