How do the Tana'im know that a husband cannot be Mekayem a wife's Neder
before she makes it?
(a) The RAN (DH Harei Hen) explains that there is simply no logical proof
that Hakamah should work before the Nedarim are made, since there is no Kal
v'Chomer (since Hakamah works to strengthen an existing Neder, it certainly
should *not* work to strengthen something that does not exist). Since we have
no proof that he can be Mekayem the Nedarim before they are made, we must
assume that he cannot.
However, the ROSH and TOSFOS, and REBBI AKIVA EIGER (on the Mishnayos),
question this explanation. If the reason there is no Hakamah before the
Nedarim are made is because there simply is no logical proof that such a
Hakamah should work, then why do the Chachamim learn from the Hekesh between
Hakamah and Hafarah that Hafarah also does not work before the Nedarim are
made, and they use the Hekesh to contradict the Kal v'Chomer of Rebbi
Eliezer? Since there are logical grounds to say that *Hafarah* can be made
before the Neder, because of the Kal v'Chomer, the Hekesh should compare
*Hakamah* to Hafarah and teach that Hakamah, too, can be made before the
Neder! In this way, the Hekesh will not contradict the Kal v'Chomer!
The TIFERES YERUSHALAYIM (on the Mishnayos) answers that the reason why
Hakamah cannot take effect before the Neder is made is because that Hakamah
would be considered a Hakamah on a "Davar she'Lo Ba l'Olam." Just like a
Neder cannot be made to prohibit someone else from a "Davar she'Lo Ba
l'Olam," so, too, one cannot make a Hakamah on a "Davar she'Lo Ba l'Olam."
However, the Ran does not seem to be using this logic. Moreover, it *is*
possible to make a Neder prohibiting a "Davar she'Lo Ba l'Olam" to *oneself*,
and thus Hakamah should be comparable to that type of Neder, because the
Torah gives the husband the right to be Mekayem someone else's Neder.
The CHASAM SOFER and PARASHAS NEDARIM answer that the Limud that compares
Hafarah to Hakamah is not an actual Hekesh. Rather, the verse -- by placing
Hakamah ("Ishah Yekeimenu") before Hafarah ("Ishah Yefeirenu") -- is teaching
that the ability to be Mekayem the Neder is a pre-requisite for the ability
to be Mefer the Neder. The verse is telling us a Halachah about Hafarah,
rather than telling us a comparison between Hakamah and Hafarah. The Parashas
Nedarim brings examples for this from TOSFOS (Shevuos 20b, DH Kol, and
Pesachim 43b, DH Salka). Even though the Ran at the end of the Mishnah refers
to the Limud as a "Hekesh," it seems clear that he does not consider it to be
a true Hekesh from what he writes earlier (end of 73a). Earlier, when the
Gemara says that one cannot be Mefer two Nedarim at one time because of the
word "Osah" (Bamidbar 30:9), the Ran says that one also cannot be *Mekayem*
two Nedarim at one time because the verse says "Lah" (30:15) regarding the
Hakamah of a Neder, and the Ran does *not* learn it from a Hekesh of Hakamah
to Hafarah. In addition, the Ran later (86b, DH l'Meimra) also makes it clear
that it is not a true Hekesh.
(b) The ROSH and TOSFOS find a different source for why a husband cannot be
Mekayem his wife's Nedarim before she makes them. The source is a logical
argument that since the husband does not know what Nedarim his wife might
make, he cannot really decide wholeheartedly that he wants to be Mekayem her
Nedarim before she makes them. She might make such a drastic Neder that he
will not want it to be upheld. Thus, his Hakamah is considered a Hakamah in
error (Hakamah b'Ta'us).
The RASHASH asks that according to this logic, a person should not be able to
be Nekayem any Nedarim that one's wife made in the *past* if he did not yet
hear them (because when he hears them he might not want them to be upheld),
but the Gemara (72b) seems to accept the possibility that a person can be
Mekayem his wife's Nedarim that she already made, before he hears them.
(c) The RASHASH says that there is an explicit Derashah in the Sifri that
teaches that a husband cannot be Mekayem the Nedarim that his wife did not
yet make. This Derashah is derived from the verse, "le'Esor Isar Al Nafsho"