QUESTION: Rebbi Yehudah teaches that if a person guards his Shor with a lesser form of Shemirah ("Shemirah Pechusah"), such as by putting it behind a gate that can withstand a Ru'ach Metzuyah (a normal, common wind) but not a Ru'ach she'Eino Metzuyah (an unusually strong, uncommon wind), and a Ru'ach she'Eino Metzuyah comes and blows down the gate and the Shor goes out and causes damage, if the Shor is a Tam the owner is liable for the damage, and if the Shor is a Mu'ad the owner is exempt.
This ruling seems to defy logic. Why should one have a greater obligation for damages of a Shor Tam than for damages of a Shor Mu'ad? Although Rebbi Yehudah derives this from a verse, what is the logic behind this ruling? Why does Rebbi Yehudah not find a more logical way to explain the verse?
Moreover, when the Gemara earlier (42a) suggests that the owner of a Shor Tam is liable for Demei Vlados while the owner of a Mu'ad is exempt, Rava challenges the suggestion and says that it is senseless, since the laws of Tam are more lenient than the laws of Mu'ad. What is the logic to explain Rebbi Yehudah's ruling?
(a) The ME'IRI, cited by the Shitah Mekubetzes, explains that since people know about a Shor Mu'ad, the obligation to avoid its damage falls equally on the people that are damaged; they are responsible to stay out of its way. Since the Nizak bears some of the responsibility, the Torah exempts a Mu'ad in a case of "Shemirah Pechusah."
According to this logic, why should a Shor Mu'ad not be exempt even when the owner does not guard it all? The answer is that if the owner lets the Shor out in the first place by not guarding it, he certainly is responsible for the Shor's actions. However, if he guards it in a way that normally would prevent it from causing damage but an Ones (circumstance beyond his control) occurred, such as a Ru'ach she'Eino Metzuyah, which allowed the Shor to escape, since there is an element of Ones involved he should not be more liable to prevent it from damaging than the person who was damaged.
This argument does not justify why the owner of a Shor Tam should pay Demei Vlados while for a Mu'ad he is exempt, and that is why the Gemara earlier considers that to be illogical.
(b) According to the opinion that Chatzi Nezek is a Kenas, since the Torah obligates the owner for damages for which he does not bear full responsibility, anytime a Shor Tam damages the law should be the same, even when the owner guards the Shor with a "Shemirah Pechusah." The Torah can obligate a person to pay a Kenas -- a penalty -- for something for which he does not bear full responsibility. However, if he guards the Shor with a "Shemirah Me'ulah" and the damage done is entirely beyond the control of the owner, the Torah does not impose any Kenas.
According to the opinion that Chatzi Nezek is Mamon, the Torah requires that the owner of a Tam pay Chatzi Nezek only because "the Torah has mercy on the owner," since he is not entirely at fault (since people do not expect the Shor to do damage when it is a Tam, as the Gemara says on 15a). Accordingly, perhaps in exchange for being more lenient with the owner with regard to the amount of payment, the Torah is more stringent with the owner with regard to the circumstances that can cause him to be liable. That is why he must pay even if he guards it with a "Shemirah Pechusah." (M. Kornfeld)
This argument does not suffice to obligate the owner of a Shor Tam to pay Demei Vlados, since the Chiyuv of Demei Vlados is unrelated to any lack of guarding on the part of the owner. That is, the Chiyuv is not related to teaching him to guard his Shor better. The Torah is stringent in that case only in order to ensure that the person does not treat lightly the damages of his Shor.
According to both of these answers, why should Rebbi Yehudah rule that one pays for the Tzad Tamus of a Mu'ad when it damages after being guarded with a "Shemirah Pechusah," as Rav Ada bar Ahavah rules? According to the Me'iri, the law should be lenient even with regard to the Tzad Tamus, since people know to be aware of the Shor! According to the second answer, the law also should be lenient with regard to the Tzad Tamus, since it certainly is not a Kenas (see Gilyon ha'Shas here), and -- since the law is not lenient with regard to paying Chatzi Nezek in the case of a Mu'ad -- there is no need to have a reciprocal stringency to obligate the owner in a case of "Shemirah Pechusah"! The logical arguments presented above seem to support the opinion of Rav (beginning of 46a) who argues with Rav Ada bar Ahavah and maintains that Rebbi Yehudah exempts even the Tzad Tamus of a Mu'ad (as the PNEI YEHOSHUA points out).
Apparently, according to Rav Ada bar Ahavah, since the Torah already ruled stringently for a Tam and required the owner to pay if it damages while being guarded with a "Shemirah Pechusah," the Torah did not remove that Chiyuv even when the Shor became a Mu'ad. This was in order to prevent the owner from benefiting ("she'Lo Yehei Chotei Niskar") as a result of allowing his Shor to gore more frequently.