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BAVA KAMA 47 - Ari Kornfeld has generously sponsored the Dafyomi publications for this Daf for the benefit of Klal Yisrael.

47b----------------------------------------47b

1) ACCEPTING RESPONSIBILITY TO WATCH THE PROPERTY OF OTHERS
QUESTION: The Mishnah (47a) teaches that when a potter places his pots in someone else's courtyard without permission and they are broken there, the owner of the courtyard (the "Ba'al ha'Bayis") is not obligated to compensate the potter for his pots. If the animal of the Ba'al ha'Bayis is damaged by the pots, the potter must compensate the Ba'al ha'Bayis.
If the potter brought his pots into the courtyard with permission and the animal of the Ba'al ha'Bayis breaks them, the Ba'al ha'Bayis is liable. Rebbi argues and says that the Ba'al ha'Bayis is never liable -- even when the potter places his pots in the courtyard with the owner's permission -- unless the Ba'al ha'Bayis specifies that he will watch the pots while they are in his courtyard.
The Gemara asks that the words of the Chachamim in the first part of the Mishnah seem self-contradictory. Is it assumed that a person automatically accepts to guard the property of another person or not? The Mishnah first teaches that when the potter brings his pots into the courtyard without permission, he is responsible for damages done to the animal of the Ba'al ha'Bayis. This implies that when he brings his pots into the courtyard with permission, he is not responsible for damages done to the animal. It is not assumed that a person (in this case, the potter) normally takes responsibility for animals or objects of others that can be damaged by his property (if his property is in a place where it has permission to be), for if a person does watch the property of another and protects it from being damaged by his own property, the potter should take responsibility for the animal even when he brings in his pots with permission. However, the Mishnah then states that when a person brings his pots into a courtyard with permission of the owner, the owner is obligated to pay for damages that his animal does to the pots. This implies that it is assumed that a person takes responsibility to protect the property of others.
Rava answers that when a potter brings in his pots with permission, the owner of the courtyard accepts responsibility for anything that happens to them, even breakage by the wind. RASHI explains that Rava means that when the Ba'al ha'Bayis invites a potter into his courtyard, his invitation ("Enter!") implies, "Enter, and I will take care of what you bring in." However, the potter never accepted responsibility for the objects of the Ba'al ha'Bayis (since, obviously, he never had to tell the Ba'al ha'Bayis to bring his items into the courtyard).
Rava apparently means that one accepts responsibility for another person's objects only when he tells the other person to bring the objects into his domain, but not simply because the objects are in his vicinity. Why, then, does the Gemara emphasize that when the Ba'al ha'Bayis tells the potter to enter, he accepts responsibility "even if the wind breaks the pots." This point seems entirely irrelevant to the answer of Rava. Rava's main point is that the potter who does not say anything does not accept responsibility! The Gemara should emphasize this point instead of emphasizing the positive aspect (that according to Rava the Ba'al ha'Bayis does accept responsibility even for that which the wind breaks)! (TOSFOS RABEINU PERETZ)
ANSWERS:
(a) TOSFOS RABEINU PERETZ explains the Gemara's answer as follows. Rava means that since the Ba'al ha'Bayis -- by inviting the potter to enter -- accepts responsibility not only for damages that his animal causes to the pots, but even for damages that come from external sources (such as the wind). Accordingly, he intends to exempt the potter from all responsibility of watching the pots. It may be assumed that the potter does not have to prevent his pots from damaging the property of the Ba'al ha'Bayis since the Ba'al ha'Bayis relieved him entirely from the responsibility of watching the pots. The main point of the Gemara is indeed that the Ba'al ha'Bayis accepted to protect the pots even from external forces that might harm them. The PNEI YEHOSHUA and RASHASH offer a similar explanation.
However, this does not seem to be the way that RASHI (DH Afilu Nishbarin) and the ROSH (5:3) explain the Gemara.
(b) According to Rashi, perhaps the Gemara means as follows. The Gemara originally assumed that the logic of the Tana of the Mishnah was that a person naturally accepts to prevent his object from damaging other objects in its proximity when both objects have permission to be there. Since this is assumed to be a universally accepted practice, the potter should also accept responsibility to protect his pots from damaging the animals of the Ba'al ha'Bayis. Rava answers that this is not the logic of the Mishnah at all, since the Tana of the Mishnah obligates the owner of the courtyard even for external forces that damage the pots. This is what the Tana means when he says that when the pots are brought in with permission, the Ba'al ha'Bayis is liable. Accordingly, it is obvious that this is not based on an unspoken assumption, since there is no reason to assume that a person takes full responsibility for the items of others just because they are in the vicinity of his items. It must be that the owner of the courtyard assumed responsibility verbally, by way of his explicit invitation that includes his acceptance to guard the objects that are brought in. Hence, there is no reason to assume that the owner of the pots took any responsibility at all for the animal of the Ba'al ha'Bayis, since he never made any verbal acceptance to do so.
According to this approach, the Gemara's words are clear. The Gemara means that the Mishnah holds the Ba'al ha'Bayis responsible not only for what his animals do to the pots, but for what anything does to the pots, because he verbally accepted to take care of the pots. On the other hand, there is no reason for the owner of the pots, who made no verbal statement, to be responsible for the possessions of the Ba'al ha'Bayis. (M. KORNFELD; the TORAS CHAIM writes a similar approach.)
Why does Rashi not explain the Gemara in the manner that Tosfos Rabeinu Peretz suggests? Perhaps Rashi bases his explanation on the Gemara later (48b) that teaches that if the two owners of two animals had permission to bring their animals into a certain place (for example, they jointly owned the property), then when one damaged the other without actively causing the damage (for example, both animals tripped on each other), both are exempt from paying for damages. According to Tosfos Rabeinu Peretz, the only reason for why the owner of the pots is exempt from damage caused to the animal of the Ba'al ha'Bayis is that the Ba'al ha'Bayis told him to enter, thereby absolving the potter from any responsibility. This reason does not apply in the case of a jointly-owned field, because neither owner needs to give permission to the other and tell him to bring in his ox; each one brings in his ox because he is a partner in the property. Rather, each owner should remain responsible for damages that his ox causes to the other!
According to Rashi's explanation, the Gemara's ruling is clear. Since neither one accepted responsibility verbally for the other one's animal, each is exempt for damages that he caused to the other.
Tosfos Rabeinu Peretz may follow his own opinion when he explains the Sugya there (48b) differently from Rashi. Tosfos Rabeinu Peretz and Tosfos there (DH Sheneihem) explain that the Gemara there refers to two people who both had permission to bring their animals into a third person's field. The Gemara does not refer to two partners who jointly own a field. The reason why the owners are both exempt from payment when their animals tripped over each other is that even if a person accepts -- without stating so explicitly -- to guard any object in the proximity of his own object, he guards the object only if he expects it to be there. If two people have permission to enter a third person's courtyard, neither of them assumes responsibility for the other because neither one has reason to be wary of which other people are permitted to enter the courtyard.

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