1) THE DIFFERENCE BETWEEN "HATARAH" AND "HAFARAH"
QUESTION: The Beraisa teaches that a Chacham may annul a Neder only through Hatarah, by saying "Mutar Lach" -- "It is permitted to you." A husband may remove a Neder only through Hafarah, by saying "Mufar Lach" -- "It is annulled for you." When a Chacham or a husband uses the wrong term, the Neder is not annulled.
The RAN and Rishonim explain that the basis for this difference is the fact that when a Chacham removes a Neder he uproots it retroactively. Accordingly, if a person transgresses his Neder and then has a Chacham annul it, he is exempted from Malkus (Shevuos 28a) because the Neder was uprooted retroactively and is considered as though it never existed. The word "Hatarah" means that he removes the Neder by making it a Neder Ta'us (a Neder made in error) and thereby renders it as though it never existed.
Hafarah, in contrast, removes the Neder only from now on. Hafarah will not exempt the woman from Malkus if she transgressed the Neder before it was annulled (Nazir 22a; see also RAN, end of 75a, DH d'Atfis). The meaning of "Hafarah" is that he annuls the Neder from now on.
The RAMBAM, however, writes the exact opposite! The Rambam (Hilchos Nedarim 13:2; see Insights to Nedarim 21:1:c) writes that a husband or father must do Hafarah and not Hatarah because Hafarah uproots the Neder from its time of origin, while Hatarah -- which a Chacham may do -- annuls a Neder only from now on. The Rambam writes this even more explicitly in Perush ha'Mishnayos, where he adds that Hafarah makes the Neder as if it never existed, while Hatarah means "undoing the knot" of the Neder for the future, and that is why the Chacham and the husband must use the appropriate terms.
The Rambam's words are very difficult to understand. The Rambam himself (Hilchos Nedarim 12:19, 13:15) rules that if the father or husband is Mefer the Neder after she transgressed it, his Hafarah does not remove the Neder retroactively and exempt her from Malkus. He clearly implies there that Hafarah removes the Neder only from now on! Moreover, the Rambam writes with regard to the Hatarah of a Chacham (Hilchos Shevuos 6:18) that Hatarah exempts a person from Malkus retroactively!
ANSWERS: The Acharonim offer many approaches for understanding the words of the Rambam. Below are a few of those approaches.
(a) The KIRYAS SEFER writes that the Rambam means that when a husband or father removes the woman's Neder, the Neder is completely removed, but when a Chacham is Matir a Neder, a part of the Isur still remains. In that sense, the husband uproots the Neder entirely, whereas the Chacham simply removes it, partially, from now on. (The Kiryas Sefer writes that this answer is somewhat forced.)
(b) The CHAZON YECHEZKEL (Hilchos Nedarim 6:1) explains that according to the Rambam, the husband's words act against the expression of Neder which his wife made, and in this sense he uproots it entirely. In contrast, the Chacham removes only the Isur of the Neder that was caused by the expression. In this sense, it is only a Hatarah for the future.
(c) Others explain that the Rambam does not refer to the effect of the Hatarah or Hafarah, but merely to the wording of the Hatarah or Hafarah. The husband must express that he wants to uproot the Neder entirely and that he does not want the Neder to have ever existed. This is necessary for Hafarah because the logic of Hafarah is that the wife makes her Neder "Al Da'as Ba'alah," on condition that her husband consents, and thus she needs her husband to consent to the original Neder in order for the Neder to take effect. (In contrast, if he only retracts his consent later, after the Neder was made, his lack of consent later will not annul the Neder.) She has in mind that if he shows later that he never consented to her Neder, from that time on the Neder should be annulled (because it does not bother him what already happened until that time).
The Chacham, however, has no right to say that the Neder never existed, even though his Hatarah uproots the Neder entirely. The Chacham says merely that from now on the Neder should no longer be effective. However, the only way the Neder can stop prohibiting the object is if the Neder never caused an Isur in the first place because it was a Neder Ta'us (a Neder made in error). Therefore, in order to cancel the Neder from now on, the Neder must be uprooted entirely (from its origin). The person who made the Neder, however, who now regrets it, admits that he wanted his Neder at the time that he made it but now he does not want it, and therefore the Chacham must use the wording that the Neder is removed from now on, according to the Rambam, in order for it to be removed retroactively from its inception. (See also the ROSH to 52a, who explains that the Hatarah of the Chacham works "from now on, retroactively" -- "mi'Kan ul'Haba l'Mafrei'a." This means that at the time the Chacham is Matir the Neder, the Neder becomes annulled from now on, and although until that point it was indeed Asur, it is viewed from now on as if there never was a Neder. Until the time of the Hatarah, the object certainly was prohibited. The Chacham, by being Matir the Neder, removes the Isur from now on as if it was never there before. See Insights to 52:1.)