1) THE REASON FOR STRINGENCY IN A CASE OF A "ROV" WHICH MANDATES LENIENCY
QUESTION: The Gemara quotes a Beraisa which teaches that if a person makes a Neder to prohibit himself from oil, and he lives in a place where most people use olive oil and a few people use sesame oil, he is prohibited from using both types of oil. Although most people (Rov) use only olive oil, he may not use sesame oil because of "Safek Isura l'Chumra."
Why should the principle of Safek Isur l'Chumra apply in this case? Whenever there is a Rov, the situation is not considered one of doubt, Safek. The Rov itself mandates that one act leniently. (See BEIS YOSEF YD 208 and SHACH YD 208:3.)
(a) The BEIS MEIR (EH 45) suggests that since a Neder is a "Davar she'Yesh Lo Matirin," one must conduct himself stringently because of the Mi'ut (minority).
The YAD SHAUL (YD 208:2) rejects this answer because "Davar she'Yesh Lo Matirin" applies only when the object is already prohibited by the Neder and then becomes mixed with other objects. When there is a doubt in the first place whether the object is prohibited, it is not considered a "Davar she'Yesh Lo Matirin" and Rov teaches that it is not prohibited.
(b) The SHITAH MEKUBETZES cites a number of Rishonim who answer that when the doubt involves how a certain wording is used, the laws of Rov and Mi'ut do not apply because the usage of a word depends on the person's intention, and not on the way the majority uses it. Although most people tend to use a word in one way, this person might use it in the way the minority uses it. Since the matter depends on a person's conscious decision and intention, the laws of Rov and Mi'ut do not apply.
The AVNEI MILU'IM (EH 45:2) cites the RITVA in Kidushin (50a) who makes a similar statement. The Avnei Milu'im also points out that this seems to be the intention of TOSFOS in Sanhedrin (3b, DH Dinei Mamonos).
The Avnei Milu'im asks that the Gemara in Bava Basra (92b) and Bava Kama (27b) presents a lengthy discussion about whether Rov applies in monetary matters, Dinei Mamonos, the same way it applies in cases of Isur v'Heter. The examples of cases of Dinei Mamonos which the Gemara there mentions are the same types of cases which the Gemara here discusses (which involve a doubt about a person's intention)! For example, a person buys an ox and then discovers that it is a Nagchan (it has a tendency to gore other animals or people) such that it cannot be kept alive and used for work but must be slaughtered and used for meat. In such a case, there is a Rov that most people who buy oxen buy them for plowing while only a few people buy oxen in order to slaughter them. Shmuel says that since some people buy oxen for their meat, the seller may claim that he sold it for the sake of slaughtering and not for the sake of plowing. It seems clear from the Gemara that this type of Rov would suffice in cases of Isurim!
The Avnei Milu'im answers that the case which the Ritva discusses is a specific case of Safek Kidushin. Perhaps the Ritva means that because of the Chumra of Kidushin we do not rely on a weak Rov (since the question is one of a person's intention and not a question of a mixture). Indeed, this is the explanation of the RAMBAN (in Milchamos) in Kidushin.
The Gemara here, however, implies that even with regard to the Isur of Neder we may not rely on such a Rov, in contrast to the words of the Avnei Milu'im.
Perhaps the meaning of the language used for a Neder is determined by the usage of the words as they are used for commerce (selling and purchasing), since commerce depends on Lashon Bnei Adam. When one sells something, his wording may include even the meaning which the Mi'ut ascribes to that wording. Therefore, in the case of a Neder as well the wording one uses for his Neder includes even the meaning used by the Mi'ut. (Accordingly, this Sugya follows the view of Shmuel in Bava Basra who rules that we do not follow Rov in monetary matters.)
(c) However, the Rishonim (cited by the Shitah Mekubetzes) apparently maintain that Rov is never used to explain a person's expressions, neither in cases of Mamonos nor in cases of Isurim. Perhaps the Rishonim understand that when the Gemara says that "we do not follow Rov in monetary matters," it does not mean that only with regard to buying and selling we do not follow Rov. Rather, it means that the type of Rov used to determine the meaning of a person's words when he buys and sells is not used even when some Isur is involved. The only type of Rov which may be used is a Rov of Ta'aruvos -- a Rov which determines the nature of an object in a mixture. This might be the intention of the Ritva in Kidushin as well. (Again, according to this explanation the Gemara here must follow the view of Shmuel. Rav, who maintains that we follow Rov in cases of monetary matters, will have to explain the Beraisa differently.)
2) APPLYING THE RULE OF "SAFEK ISUR L'CHUMRA" TO NEDARIM
QUESTION: The Gemara quotes a Beraisa which teaches that if a person makes a Neder to prohibit himself from oil, and he lives in a place where most people use olive oil and a few people use sesame oil, he is prohibited from using both types of oil. Although most people (Rov) use only olive oil, he may not use sesame oil because of "Safek Isura l'Chumra," and the Rov is disregarded (see previous Insight).
The Gemara earlier in Nedarim (18b) teaches that when a person makes a Neder in which he compares a certain object to "Yayin Nesech" with intent to prohibit the object, there is a doubt whether his intent is to compare the object to Yayin Nesech of a Korban or Yayin Nesech of Avodah Zarah. The Mishnah states that the Neder takes effect and the object becomes forbidden despite the doubt because of the principle of "Stam Nedarim l'Hachmir." The Gemara there (19a) cites an opinion which disagrees with the Mishnah and says that "Safek Nedarim l'Hakel."
Why does the Gemara here apply a different rule, that of "Safek Isur l'Chumra" (with which all of the Tana'im agree), instead of the rule of "Stam Nedarim l'Hachmir"? Conversely, if the rule of "Safek Isur l'Chumra" applies here, why does the Mishnah earlier (18b) not prohibit the object because of this reason?
ANSWER: There are two different types of Safek Neder. In the case of the Gemara here, the person made a valid Neder which takes effect; the doubt involves merely the extent of the Neder (i.e. how much the person intended to prohibit). This doubt is treated like every other Safek Isur (and thus one must conduct himself l'Chumra).
In contrast, in the case of the Gemara earlier (18b) the doubt is whether the person is expressing a Neder at all. If he means to say that "this object is like Yayin Nesech of Avodah Zarah," then he is not making a Neder at all. If he means to compare the object to Yayin Nesech of a Korban, then he is making a Neder. In that case, the Neder takes effect not only out of doubt (because of the rule of Safek Isur l'Chumra), but it definitely (Vadai) takes effect because of the rule of "Stam Nedarim l'Hachmir," and one who violates such a Neder will even receive Malkus. The reason why this Neder takes effect is that since the person did not remain quiet, it is assumed that he intended to make a Neder and not a meaningless statement (as the ROSH explains).
However, this distinction does not explain the other cases cited by the Gemara (18b and 19a) as examples of cases in which the principle of "Stan Nedarim l'Hachmir" may apply. The Gemara cites the case of a person who declares that all of his Chayos and Behemos are Hekdesh. The Tana'im argue whether the person's Koy is included in his Neder out of doubt (mi'Safek). There is a doubt whether a Koy is a Chayah, Behemah, or an independent entity. Since the person is Makdish his other animals, his statement certainly is not meaningless if a Koy is not included in his Neder. Why, then, should we assume that he also intends to be Makdish the Koy? That case should be the same as the case of the Gemara here; the doubt is the extent of the Neder, and the principle of "Stam Nedarim l'Hachmir" does not apply in such a case. Similarly, the Gemara cites a case in which a person says that he will become a Nazir if there is a certain amount of grain in a certain pile, and then the grain in that pile was stolen and he could not determine how much there was. The Tana'im argue whether he becomes a Nazir mi'Safek. In that case, however, the person made the statement of Nezirus not because he wanted to be a Nazir but because he wanted to prove that he knew how much grain was in the pile. Even if he does not become a Nazir, his statement was not meaningless. Moreover, the Gemara says that even if he is a Nazir, he is only a Safek Nazir and not a Vadai Nazir. The Gemara there clearly does not apply the logic of the Rosh. Why, then, do the Tana'im argue in those cases, while in the Gemara here they agree that the Safek Neder is prohibited because of "Safek Isur l'Chumra"?
The answer seems to be as follows. In each case of the Gemara earlier (18b and 19a), the Safek is independent of the person's Neder. In one case, the Safek is whether a Koy is a Chayah, Behemah, or independent entity. In another case, the Safek is how much grain was in the pile. In such cases, some Tana'im maintain that a person does not want his Neder to take effect if it will take effect only out of doubt ("a person does not put himself into a situation of Safek"). In the case of the Gemara here, however, there is no independent Safek. The doubt is the very intention of the Noder himself. In such a case, it is illogical to say that the person does not want to put himself into a situation of Safek and thus the Neder should take effect on sesame oil, because the Safek was created by his own expression of the Neder. This type of Safek certainly takes effect because he said his Neder with no qualifications; he did not say what it should not take effect upon. The principle of "Safek Isur l'Chumra" certainly applies to a Safek which he creates himself. Only when the Safek is not one which he creates himself does he not have intention for his Neder to take effect because of the Safek. (That is, only when he knows that he is getting involved in a Safek is it possible to say that he intends to create an Isur even though there is a Safek. When he has no idea that there is a Safek and he is innocently trying to make an ordinary Neder, we certainly cannot assume that he intends to make something Asur mi'Safek.)