1) A NEDER TO UPROOT A MITZVAH
QUESTION: The Gemara teaches that a Neder to transgress a Mitzvah takes effect, but a Shevu'ah to transgress a Mitzvah does not take effect. A Neder creates a prohibition on the object (Isur Cheftza), while a Shevu'ah creates a prohibition on the person (Isur Gavra). Since the person is obligated by the Torah to do the Mitzvah, he cannot make a Shevu'ah to uproot that Mitzvah and override his obligation. In contrast, a Neder takes effect to uproot a Mitzvah, since the Neder does not directly oppose the obligation which rests upon the person; he does not make himself prohibited from the object of the Mitzvah, but rather he prohibits the object to him.
Practically, why is there a difference between a Neder and a Shevu'ah? In both cases, one attempts to prohibit himself from doing a Mitzvah. Since he is obligated by the Torah to do the Mitzvah, not even a Neder should take effect to uproot it.
(a) The Gemara (15b) explains that a man may prohibit himself from marital relations with his wife -- even though the Torah obligates him to provide her with her needs -- by prohibiting to himself any pleasure or benefit that comes from her. Since the Mitzvah requires him to provide her with pleasure, and his Neder prohibits her pleasure to him, the Neder takes effect. Once it takes effect to prohibit her pleasure to him, he becomes prohibited to have marital relations with her. In contrast, if he says that any pleasure or benefit from him is prohibited to her, the Neder cannot take effect because the Neder is in direct opposition to the Mitzvah.
Similarly, the RAN and others (see RAMBAN in Milchamos to Shevuos, end of Perek 3) explain that in this case, when a person makes a Neder to prohibit the object of a Mitzvah on himself, the Neder is not in direct opposition to the Mitzvah because the Neder prohibits the Cheftza and not the Gavra. Once the Neder takes effect on the Cheftza, it is only a secondary consequence that the person cannot do the Mitzvah. A Shevu'ah, on the other hand, takes effect on the Gavra, and thus it cannot override the pre-existing obligation on the Gavra to do the Mitzvah.
(b) The SHITAH MEKUBETZES suggests that when a person makes a Neder (an Isur Cheftza), it appears as though he is making the object of the Mitzvah (such as a Sukah) prohibited to him because it is not comfortable. In contrast, when he makes a Shevu'ah (an Isur Gavra), it appears as though he has a personal aversion to the Mitzvah, but not because the Sukah itself is undesirable. Since his Shevu'ah directly opposes the Mitzvah, it cannot override the Mitzvah and it does not take effect.
(c) The AVNEI NEZER (YD 294) infers from the SEFER HA'CHINUCH (Mitzvah 30) a different line of reasoning. One fulfills the Mitzvah of Sukah by sitting in any Sukah. Therefore, if a person makes a Neder to prohibit himself from benefiting from any Sukah, the Neder takes effect on all Sukos. On each individual Sukah there is no reason for the Neder not to take effect, since the Mitzvah may be fulfilled with any other Sukah. Since the Neder takes effect on each Sukah individually, the person is left with no Sukah with which to fulfill the Mitzvah.
A Shevu'ah, on the other hand, is an Isur Gavra -- the Isur takes effect on him and it prohibits him from sitting in any Sukah. Therefore, the Shevu'ah cannot take effect because it is in direct opposition to the Mitzvah.
The Avnei Nezer suggests practical differences between the logic of the Ran and the logic of the Sefer ha'Chinuch. What is the Halachah in the case of a person who makes a Neder to prohibit himself from covering the blood (Kisuy ha'Dam) of a bird that was just slaughtered? According to the Ran, the Neder takes effect on the blood (the Cheftza) and, consequently, he is not allowed to cover it. According to the Sefer ha'Chinuch, a Neder takes effect to uproot a Mitzvah only when the Mitzvah can be fulfilled with another object. In the case of a Neder not to do the Mitzvah of Kisuy ha'Dam, there is only one object with which to fulfill the Mitzvah (the blood of that bird), and therefore the Neder should not take effect.
The Avnei Nezer's practical difference is debatable. Although the Ran explains that a Neder may be made to prohibit an act which does not involve benefit (for example, one may prohibit a stone from being thrown into the sea), that logic does not necessarily permit a person to prohibit himself from doing Kisuy ha'Dam. The Mitzvah of Kisuy ha'Dam is not an act done with the blood but an act done to the blood. Therefore, an Isur Cheftza on the blood cannot prohibit one from doing something to the blood (covering it with dirt), but only doing something with the blood. Moreover, it is not necessary to cover all of the blood to fulfill the Mitzvah; one fulfills the Mitzvah by covering merely part of the blood (Shulchan Aruch YD 28:15). Hence, the Neder should be able to take effect on each drop of blood, just as it could take effect on each and every Sukah according to the Avnei Nezer.
However, another practical difference may be in a case in which a person makes a Shevu'ah to eat an entire loaf of bread, and then he makes a Neder to prohibit himself from the bread. Since the Shevu'ah obligates him to eat every k'Zayis of the bread, the Neder (according to the Avnei Nezer) should not take effect since there is no k'Zayis of the bread on which it can take effect. According to the Ran (and other Rishonim, 18a), in such a case the Neder should take effect and override the Shevu'ah.
2) PLEASURE DERIVED FROM A MITZVAH
QUESTION: Rava argues with Abaye and says that if a person makes a Neder to prohibit himself from the pleasure of sitting in a Sukah, he is allowed to sit in a Sukah Shel Mitzvah because "Mitzvos Lav l'Hanos Nitnu," the pleasure of a Mitzvah is not considered pleasure.
Rava's ruling is difficult to understand. The RAN earlier (end of 15b) writes that only pleasure from the actual fulfillment of the Mitzvah is not considered Hana'ah. Physical pleasure derived from the act of performing the Mitzvah is considered Hana'ah! The Ran proves this from the Gemara in Rosh Hashanah (28a) which says that when one prohibits himself from receiving pleasure from a wellspring, he is permitted to immerse in a wellspring in the winter but not in the summer, because in the summer he enjoys physical pleasure from the wellspring in addition to the pleasure of fulfilling the Mitzvah of Tevilah. Accordingly, in the case of the Gemara here, the person should be prohibited from sitting in a Sukah Shel Mitzvah since -- in addition to the pleasure he receives from the Mitzvah -- he enjoys the physical pleasure of the Sukah's shade. (SHALMEI NEDARIM in the name of the MACHANEH EFRAIM, Nedarim #25, the NODA B'YEHUDAH OC 2:132, and the BEIS MEIR YD #215)
(The RASHBA (15b) indeed disagrees with the Ran and maintains that even incidental Hana'ah which one receives while doing a Mitzvah is not considered Hana'ah.)
The BEIS MEIR adds that the Ran himself writes later (39a, DH v'Iy) that if a person prohibits himself from Hana'ah from a sick person and from his property, he is not allowed to visit the sick person because he has Hana'ah when he walks into the person's home. Although he is involved in the performance of a Mitzvah (visiting the sick), he benefits from the sick person's property, which provides him with a place to stand. Similarly, the act of sitting in a Sukah also provides one with physical pleasure, besides the pleasure of fulfilling the Mitzvah, and thus the Neder should prohibit it.
(a) The SHALMEI NEDARIM first suggests that mid'Oraisa the person's Neder does not take effect to prohibit him from sitting in a Sukah, because no form of pleasure which one experiences from a Mitzvah is considered Hana'ah (this is the intent of Rava). However, the Rabanan decreed that the person's Neder takes effect to prohibit the secondary forms of Hana'ah which he experiences as he performs the Mitzvah.
(b) The Shalmei Nedarim further suggests that perhaps Rava's argument is not from the case of one who makes a Neder to prohibit the pleasure of sitting in a Sukah, but the case of one who makes a Neder to prohibit himself from the pleasure of holding a Lulav. At the moment he holds the Lulav and fulfills the Mitzvah, he experiences no physical pleasure. Therefore, one who makes a Neder and says "Hana'as Lulav Alai" ("the pleasure of holding a Lulav is forbidden upon me"), he should not be prohibited from doing the Mitzvah.
(c) The RAN (16b) maintains that the only form of Hana'ah of a Mitzvah which one may prohibit upon himself is Hana'as ha'Guf, pleasure which the body itself experiences. Perhaps the Ran means that a person is able to prohibit only Hana'ah which involves physical contact at the same time he performs a Mitzvah, such as the Hana'ah of immersing in a wellspring, the Hana'ah of marital relations, and the Hana'ah of standing on someone's property. In contrast, when a person prohibits himself from the Hana'ah of a Sukah, his intention is to prohibit himself from benefiting from the Sechach, the main part of the Sukah. Hence, even if he benefits from the shade of the Sechach, that benefit does not involve physical contact and therefore his Neder does not prohibit that type of Hana'ah since it comes at the time of the fulfillment of the Mitzvah. (M. KORNFELD)
(d) Perhaps the only form of Hana'ah which one's Neder can prohibit is Hana'ah which is not necessary in order to accomplish the Mitzvah. When the Mitzvah can be fulfilled without that Hana'ah, that Hana'ah is prohibited. Accordingly, in the case of one who makes a Neder not to immerse in the wellspring, he may not immerse in the summer because it is possible to avoid the physical Hana'ah of the cool water by immersing in the winter. Similarly, one can visit the sick without experiencing any Hana'ah from the sick person's property, such as by standing outside of his house. Since the Hana'ah of standing on his property is not necessary in order to accomplish the Mitzvah, the Neder takes effect on that Hana'ah. In the case of the Neder against marital relations, one is able to do the act in a manner in which he experiences no Hana'ah, "k'Mi she'Kafa'o Shed" (as the Gemara says on 20b). Since the average person is unable to exercise such a degree of self-control, practically the Neder takes effect to prohibit the act even though it is a Mitzvah, because of the Hana'ah which he experiences independent of the Mitzvah. In contrast, sitting in a Sukah is not possible to do without experiencing Hana'ah from the Sechach (when it protects him from the sun). (M. KORNFELD)