The beginning of this week’s parshah discusses the halachos of a parah adumah (red heifer). The parah adumah is shechted and burnt, and its ashes are sprinkled on one who is tamei meis on the third and seventh days. The individual thereby becomes pure.
The Gemara in Chullin 11a seeks a source in the Torah for the halacha that one may follow a rov (majority) found in nature or tendencies (ruba d’lessa kaman). For example, most animals in the world are not treifos. Therefore, we can assume that the animal before us is not a treifah – even without checking. One of several suggestions the Gemara makes is that we can derive this from the parah adumah. The Gemara explains that we learn from the pasuk, “veshachat vesaraf – and you shall slaughter and burn it,” that just as a cow must be intact when it is slaughtered, so too the cow must be intact when it is burnt. Thus the cow may not be opened and checked to determine whether it is a treifah. The Gemara says that since the Torah refers to the parah adumah as a chatas, it is not allowed to be a treifah. The Gemara asks how we can be certain that the cow is not a treifah considering that it must be intact and cannot have its insides checked to determine whether it is a treifah. This is proof that the Torah intended for us to rely on the fact that the majority of cows is not treifah.
Tosafos (Chullin 11a, d”h minah) quotes from the Ba’alei Tosafos Rabbeinu Chaim that we learn another halacha – as it regards following a rov – from parah adumah. He says that we draw from this that in a situation that has a rov but has a chazakah that states the opposite, we follow the rov. This is known as ruba v’chazakah, ruba adif. We see that despite the fact that a chazakah is standing against the rov, the Gemara says that we follow the rov. The chazakah here is that the individual was certainly tamei prior to the sprinkling of the ashes, but now a doubt arises as to whether the cow was a treifah and fit to be a parah adumah. The chazakah of the person indicates that he should remain in his current status, namely to remain tamei. But since the rov says that the animal is not a treifah, we follow the rov – and the person is tahor.
Rav Akiva Eiger (Teshuvos Tinyanah 129) asks the following question on Tosafos: We know that a rov that has already been relied upon for other halachic matters takes on a stronger status. For example, in order for an animal to be counted toward ma’asar beheimah it must be certain – without any doubts. However, an animal that is a treifah is disqualified. How can we be certain that any animal can be counted toward ma’asar beheimah when perhaps it is a treifah? And even if we rely on the fact that the animal belongs to the rov of animals that are not treifah, this is only a majority; one still cannot be certain. Says Rav Akiva Eiger: Since we have relied on the rov and already assumed that the animal was not a treifah for other halachic matters, the animal is now certainly believed to not be a treifah.
Another example of this concerns the halacha that one who is a safek mamzer may marry another person who is also a safek mamzer. If a mamzer is a safek and there is a rov that says that he is not a mamzer, he remains permitted to marry another safek mamzer even though it is a safek. Asks Rav Akiva Eiger: Every person in the world is known to not be a safek mamzer because we apply the principle of rov, namely that the majority of women have children from their husbands. Since we only know this by means of a rov, every person should be permitted to marry a safek mamzer. Rav Akiva Eiger answers that since we have already relied on the rov for other matters, it takes on the status of certainty.