1) RECIPROCAL BENEFIT
QUESTION: The Mishnah states that one who makes a Neder to prohibit his friend from receiving pleasure from him may not lend to his friend or borrow from him, and he may not sell to him or buy from him. Abaye explains that although the Noder does not give pleasure to his friend by borrowing from him, the Chachamim made a Gezeirah that he not borrow so that he not come to lend to him. Similarly, based on this reasoning they prohibited him from buying from his friend so that he will not come to sell to him.
However, the Mishnah later (47b) states that when one prohibits his friend from receiving pleasure from him, his friend may not have pleasure from the Noder but the Noder is permitted to have pleasure from his friend. This ruling seems to contradict Abaye's statement that the Chachamim made a Gezeirah that the Noder not have any pleasure from the Mudar in order to prevent him from giving pleasure to the Mudar.
(a) The RAN answers that the Gezeirah of the Mishnah was instituted only with regard to borrowing and buying, since people do not usually relate to these acts as acts of giving pleasure. The Chachamim were concerned that if the Noder is permitted to borrow from the Mudar, people will think that borrowing and lending are not considered acts of giving Hana'ah and they will assume that the Mudar is also permitted to borrow from the Noder. In contrast, allowing the Noder to accept a gift from the Mudar will not lead people to assume that the Mudar Hana'ah is also permitted to receive a gift from the Noder, because it is obvious that giving a gift is an act of giving Hana'ah.
(b) TOSFOS (DH Beshleima; see also ME'IRI) and the RITVA answer that the Chachamim made the Gezeirah only with regard to favors which people always reciprocate to one another. One who lends to his friend usually borrows from his friend in turn in his time of need. Therefore, there is a concern that if the Mudar Hana'ah is permitted to lend to the Noder, the Noder will eventually return the favor and lend to the Mudar Hana'ah. This concern does not exist for other forms of Hana'ah which are not usually reciprocal.
2) THE NATURE OF HEFKER
OPINIONS: The Mishnah states that if one makes a Neder to prohibit his friend from receiving pleasure from him, and his friend has no food to eat and no one else is available to feed him, he may declare his food to be Hefker for all and then his friend may come and take it. Rebbi Yosi disagrees and prohibits him from declaring his food Hefker so that the Mudar Hana'ah may take it.
In the Gemara, Rebbi Yochanan says that the dispute is based on each Tana's understanding of the nature of Hefker. The Chachamim (the Tana Kama) understand that as soon as one makes his property Hefker it no longer belongs to him. Since it does not belong to the Noder, the Mudar is permitted to benefit from it. Rebbi Yosi understands that even after a person makes his property Hefker it is still considered to be in his possession until someone else actually acquires it. Hence, the Mudar may not take the food which the Noder made Hefker since it is still the Madir's food which is prohibited to him.
Rava proves that Rebbi Yosi agrees that Hefker does not belong to its original owner. He says that Rebbi Yosi disagrees with the Tana Kama only because of a Gezeirah d'Rabanan.
What is the nature of Hefker? Does a declaration of Hefker remove an item from the possession of the original owner completely, or does it remain in his possession until someone else takes possession of it?
(a) The RAMBAM (Hilchos Nedarim 2:14) writes that although a declaration of Hefker is not a Neder, it resembles a Neder in that one who declares his item as Hefker is prohibited from retracting his word and taking the item back into his possession. The Rambam's wording implies that the person has the power to retract the Hefker but is prohibited from doing so. The KETZOS HA'CHOSHEN (273:1) understands that the Rambam means that even after the person has made the item Hefker, it is still in his possession. He is prohibited to retract the Hefker only because Hefker is a type of Neder and by retracting it he transgresses the prohibition of "Lo Yachel Devaro."
(b) Many Acharonim (see CHIDUSHEI CHASAM SOFER ad loc., and SHA'AREI YOSHER 5:23) disagree with this interpretation of the Ketzos ha'Choshen. They point out that the Chachamim in the Mishnah here maintain that Hefker does not belong to the original owner who made the item Hefker (and, according to Rava, even Rebbi Yosi agrees).
The VILNA GA'ON (CM 273) emends the Girsa of the Rambam so that it reads that one who makes something Hefker is "unable" (and not "prohibited") to retract it. According to this Girsa, the Rambam's ruling follows that of the Chachamim who maintain that when one makes an item Hefker it is no longer in his possession.
However, if the Rambam agrees that Hefker is not only a Neder but is an actual monetary transaction which changes the ownership of the item (from the domain of the original owner's to the domain of nobody), why does the Rambam record the laws of Hefker among the laws of Nedarim (Hilchos Nedarim)? Moreover, why does the Rambam mention that a declaration of Hefker is similar to a Neder?
The CHASAM SOFER (Teshuvos, YD 316) writes that the Rambam maintains that Hefker is a type of Neder, whereby one binds himself to make a certain object ownerless. However, the actual declaration of the item as Hefker is a fulfillment of the Neder, and therefore the item no longer belongs to him.
The SHA'AREI YOSHER (loc. cit.) explains that the Rambam does not mean to say that Hefker is a Neder. His correlation between Hefker and Nedarim means merely that just as a Neder creates a new Halachic status (it makes an item Hekdesh, Asur, or Tzedakah), so, too, Hefker creates a new Halachic status for the item (it takes the item out of the possession of the original owner).