OPINIONS: The Gemara quotes a Beraisa which states that when one hides his thorns or glass in a wall and the owner of the wall eventually knocks down the wall in such a way that it falls into the public domain, the owner of the thorns or glass is liable for any damage that his object causes. Rebbi Yochanan explains that he is liable only when the wall was weak. RASHI (DH b'Kosel Re'u'a) explains that since the wall was weak, the owner of the thorns should have realized that the wall would be knocked down and that his thorns would cause damage.

Why, though, is the owner of the wall entirely exempt? Since he was the one who knocked down the wall into the public domain and caused the thorns to be in a place in which they could do harm, he should be at least partially liable for the damage.

(a) RASHI (DH Mahu d'Teima) and TOSFOS (DH v'Chayav) write that although the owner of the wall was aware of the thorns when he knocked down the wall, he had no obligation to do anything with the thorns because he did not know who owned the thorns.

The BIRKAS AVRAHAM explains the intention of Rashi and Tosfos. At the moment the thorns are placed in a wall that will likely be knocked down, they are considered a Bor. Since a natural and foreseeable occurrence, such as a strong wind, will bring the thorns to cause damage, it is considered as if the owner of the thorns has thrown a damaging object (Bor) towards the public domain, and it merely has not yet landed in the public domain. Accordingly, when the owner of the wall knocks it down, he is merely adding a small degree of negligence to a pre-existing Bor.

This is why the Gemara compares this case to a case in which one covered his Bor with his friend's pail. If his friend takes away his pail, the owner of the Bor is liable for the resultant damage, even though it was his friend who uncovered the Bor. This is because the obligation to prevent the Bor from causing damage falls on the person who creates the Bor. When the Bor is not being watched or covered, the liability rests on the owner of the Bor.

This explanation is novel in that it asserts that the thorns are considered a Bor immediately, even though they are not yet resting in the public domain.

(b) The NIMUKEI YOSEF seems to have a different approach. He writes that the owner of the wall is exempt because he had no reason to suspect that someone put thorns into his weak wall. The Nimukei Yosef clearly understands that the owner of the wall did not know about the thorns inside his wall, and hence he is exempt from any liability.

The Birkas Avraham explains that according to the Nimukei Yosef, the thorns are not considered a Bor before they fall into the public domain. The owner of the thorns is Chayav because his actions, together with a natural occurrence, brought a Bor into the public domain.

The Birkas Avraham describes a case in which there is a practical difference between these two approaches, that of Rashi and Tosfos and that of the Nimukei Yosef. What is the law if a third person knocks down the wall? Is he liable to pay for the damages caused by the thorns, or does the liability still rest on the owner of the thorns?

According to Rashi, who explains that the thorns are already considered a Bor, it should make no difference who knocks down the wall. In any case, the owner of the thorns has created a Bor and is liable. This indeed is the ruling of the ME'IRI. The Gemara discusses the case of a person who covered his Bor with someone else's pail. The owner of the pail subsequently took his pail from atop the Bor. The Gemara states that the owner of the Bor is liable for any damage that his Bor causes as a result of being uncovered. The Me'iri writes that even if someone other than the owner of the pail takes away the pail, the owner of the Bor is liable because he failed to prevent his Bor from causing damage.

In contrast, the Nimukei Yosef quotes the RAMAH who rules that if someone other than the owner of the wall knocks down the wall without permission of the owner, the one who knocks it down is liable. Although the owner of the thorns was negligent, the one who knocked down the wall finished the formation of the Bor, and thus he is liable. This ruling is consistent with the Nimukei Yosef's logic explained above, that the thorns do not yet have the status of a Bor until they actually fall into the public domain. Therefore, anyone who brings the Bor to the public domain is liable. He may not claim that he did not know there were thorns in the wall (as the owner of the wall may claim), since he knocked it down without permission. (Mordechai Zvi Dicker)

QUESTION: The Gemara relates that the Chachamim penalized one who leaves his straw in the public domain so that passers-by will tread on it (and thereby turn it into fertilizer), and they permitted anyone to take his straw. Rav says that this penalty applies even if the straw was not yet trampled. Although this is the Halachah, the Tana Kama maintains that "Halachah v'Ein Morin Ken" -- "this is the law, but we do not instruct thusly." That is, if one asks whether he is permitted to take the straw before it has been trampled, the Rav tells him that he may take it only after it has been trampled. If, however, he takes the straw before it has been trampled, he is not forced to return it since he acted in accordance with the letter of the law.

The MAHARATZ CHAYOS points out that the concept of "Halachah v'Ein Morin Ken" generally means something else. One who inquires in private should be told the correct Halachah, but that Halachah should not be taught in public. The Gemara here clearly means that one who asks should not be told the actual Halachah (as RASHI writes in DH b'Halachah). The Gemara asks that if "Halachah v'Ein Morin Ken" applies here, why did Rav Huna rule that barley left in the public domain is ownerless? If "Halachah v'Ein Morin Ken" means that the Halachah is told to someone only in private, perhaps Rav Huna only ruled this way for those who asked him in private! It must be that the Gemara means that the Halachah, in this case, is not taught even in private.

Why, though, does the Gemara here use this phrase differently from the way it uses it in all other places? (See, for example, Shabbos 12a, Beitzah 28b.)

ANSWER: Perhaps the concept of "Halachah v'Ein Morin Ken" is generally used with regard to a leniency which the Chachamim do not want to publicize, lest people become lax in their observance of matters of Isur v'Heter. Teaching the leniency only in private will prevent it from becoming publicized. In contrast, the Gemara here is not discussing a leniency, but rather a penalty. It is therefore understandable that when "Halachah v'Ein Morin Ken" is mentioned in the context of a person who seeks to take advantage of the penalty which the Chachamim applied, the Chachamim do not encourage such behavior by revealing that it is permitted, as such a ruling will cause disputes.

This explanation may have a basis in the words of the ME'IRI. The ME'IRI writes that the reason why we do not rule this way is because of "Tikun ha'Olam," which implies that we seek to avoid disputes. (See note 95 in OTZAR MEFARSHEI HA'TALMUD here.) (Mordechai Zvi Dicker)