The Gemara concludes that an Aseh is not Docheh a Lo Ta'aseh that has Kares.
Therefore, the Gemara searches for a reason why we would have thought that
the Mitzvah of Yibum is Docheh the Lo Ta'aseh of Arayos, such that we need a
verse to tell us that it is not Docheh the Lo Ta'aseh.
Why does the Gemara not learn from the case of Yibum that an Aseh *is* Docheh
a Lo Ta'aseh that has Kares? The Torah tells us that the Mitzvah of Yibum
overrides the Lo Ta'aseh she'Yesh Bo Kares of "Ashes Ach." Even though the Lo
Ta'aseh of Eshes Ach has Kares, the Torah states that it is permitted to
marry one's brother's wife in order to fulfill the Mitzvah of Yibum! We can
learn from there that an Aseh *is* Docheh a Lo Ta'aseh that has Kares!
Consequently, we need another verse ("Aleha") to teach that in the case of
Yibum with another Ervah, the Mitzvah is *not* Docheh the Lo Ta'aseh that has
Kares. Why did the Gemara not give this answer?
(a) TOSFOS (4a, DH Lo Ta'aseh) explains that nothing can be derived from the
verse that teaches that the Isur of "Eshes Ach" is pushed aside for Yibum.
The reason is because the Mitzvah of Yibum can never be performed under any
circumstances without overriding the Isur of "Eshes Ach" (this is called
"Mitzvaso b'Kach" -- the Mitzvas Aseh can *only* be performed by overriding a
Lo Ta'aseh). We cannot derive from this case that in all other situations of
an Aseh conflicting with a Lo Ta'aseh that has Kares, that the Aseh overrides
the Lo Ta'aseh, because in all other cases there are circumstances in which
the Aseh can be done *without* overriding the Lo Ta'aseh.
In KOVETZ HE'OROS (9:1), Rav Elchanan Wasserman, Hy'd, explains that Tosfos
means to say that this is a *Pircha* to the suggestion that we learn this law
of "Aseh Docheh Lo Ta'aseh she'Yesh Bo Kares" from Yibum through a Binyan Av.
That is, Yibum is different from all other cases of an Aseh conflicting with
a Lo Ta'aseh that has Kares, because in this case, Yibum can *never* be done
without being Docheh the Lo Ta'aseh. We find an example of such a Pircha in
(b) The YAD RAMAH (Sanhedrin 53b) suggests a different logic. Since Yibum can
only be done with an "Eshes Ach,' it is clear that the Torah never prohibited
"Eshes Ach" in the first place in a situation of Yibum. (The Isur of "Eshes
Ach" is "Hutrah," and not "Dechuyah.") This is different from all cases of an
Aseh being Docheh a Lo Ta'aseh, where the Lo Ta'aseh is still in force, but
the Aseh is more important and pushes it aside. In the case of Yibum, there
is no Lo Ta'aseh of "Eshes Ach" whatsoever. This is why the Gemara cannot
suggest that we learn from Yibum that an Aseh is Docheh a Lo Ta'aseh that has
This is clear from a number of laws of Yibum. If performing Yibum is
permitted because it overrides the prohibition of "Eshes Ach," then once the
surviving brother has lived with the Yevamah one time and thereby fulfilled
the Mitzvah of marrying his deceased brother's wife, why is he permitted to
be with her again ("Bi'ah Sheniyah")? The Gemara (20b) tells us that if the
Yevamah is prohibited to the Yavam with an Isur Lo Ta'aseh, although Yibum is
Docheh the Lo Ta'aseh, the Yavam must divorce her immediately afterwards, and
he is not permitted to be with her again!
Furthermore, the Halachah is that if a Yavam divorces the Yevamah after
performing Yibum, he is permitted to remarry her. If the Mitzvah of Yibum
merely pushed aside, temporarily, the prohibition of "Eshes Ach," then why is
he permitted to remarry her? He is not fulfilling any Mitzvah by doing so!
The answer, explains the Yad Ramah, is because the Torah never prohibited an
"Eshes Ach" in a situation of Yibum, and therefore she is completely
permitted even after the Mitzvah has been fulfilled. No Dechiyah is necessary
to permit her. (The Gemara itself demonstrates this difference between a
"Dichuy" (that only pushes aside an Isur temporarily) and a "Heter" (that
pushes aside an Isur absolutely). The Gemara (7b) says that "Ho'il d'Ishteri
Ishteri" -- once the Isur becomes permitted, it becomes permitted absolutely,
so that other Isurim related to it also become permitted.)
The same theme is proposed by the RAMBAN in Toras ha'Adam (cited by Kovetz
He'orors, ibid.), RASHBA (Kidushin 21b), RITVA (here), and the RA'AVAD (Tamid
end of 27a), who write, regarding Yibum and other Mitzvos, that when an Isur
is "Hutrah," it is considered a completely different category than an Isur
that has been pushed aside because of a Mitzvah. In the former case, the
Heter is a permanent one, while in the latter case, the Heter is only
Tosfos' words indeed need clarification. Why should he consider Yibum to be
an example of an Aseh that overrides a Lo Ta'aseh? If Yibum is permitted only
because of the Mitzvas ASeh, why is it permitted for the brother to stay
married to his brother's wife? Once he marries her and lives with her for the
first time, he has fulfilled the Mitzvah of Yibum and there is no longer a
Mitzvas Aseh to be Docheh the Lo Ta'aseh, and he should divorce her, like the
Gemara says on Daf 20b! In addition, why is it permitted for him to remarry
her once he divorces her? The Isur of "Eshes Ach" should prohibit him from
remarrying her, since there is no fulfillment of any Mitzvah! (See KEREN ORAH
Apparently, Tosfos felt that it was unacceptable to suggest that the Isur of
Eshes Ach is "Hutrah," and does not apply at all to a Yevamah. It is clear
from the Gemara that the Isur *does* remain even on the Yevmah, and it is
only pushed aside at the time the Yavam does Yibum, due to the Mitzvah of
Yibum. This is clear from the Gemara later (10b), which tells us that
according to Reish Lakish, after one of the Yivmim takes one of the Yevamos
as his wife, the brothers of the Yavam remain prohibited to the other wives
of the deceased b'Isur Kares, since the Torah never removed the Isur Eshes
Ach from them. Similarly, Rebbi Yochanan argues and maintains that the other
brothers remain prohibited to the other wives only through an Isur Lav
because "the Yavam took his Yevamah as a "Shali'ach" for all of his brothers
and for all of her Tzaros" (and just like the Torah removed the Isur Kares
for him when he took her, so too it removed the Isur for all of the others).
It is the Yibum that removes the Isur Kares; the Isur does not become
annulled at the time of the death of the brother, as one would expect if it
This approach is also evident in the words of RASHI (52b DH Nasan), who
writes that the Yavam cannot be Mekadesh the Yevamah with normal Kidushei
Kesef since she is "Eshes Achiv," and Kidushin cannot be made with an Ervah.
(See also TOSFOS, top of 49b.) Further support can be brought from the
opinion of Aba Shaul (Yevamos 39b), who maintains that one who performs the
Mitzvah of Yibum with ulterior motives, is "close to living with an Ervah."
If the Torah permitted this woman to the Yavam, how can the Yavam's
intentions affect her Heter? What does she have in common with an Ervah?
For these rasons, Tosfos understood that Yibum can indeed be interpreted in
terms of "Aseh Docheh Lo Ta'aseh." The reason Bi'ah Sheniyah is permitted
(the Yavam does not have to immediately divorce her) and the reason he may
re-marry the Yevamah after divorcing her, is because the Torah extends the
Heter of the Yevamah *after* the initial Dechiyah of her Isur through the
Mitzvah of Yibum (see 8b, and TOSFOS DH Melamed). The initial act is one of
Dechiyah, only afterwards does the Torah remove the Isur Eshes Ach entirely,
so that the Yavam may raise a family from his brother's wife.
The other Rishonim perhaps do not argue with Tosfos that the general Isur of
Eshes Ach remains until the moment of Yibum. Nevertheless, they maintain
that the Torah permits performing an "act of Yibum" with the Eshes Ach from
the moment the childless brother passes away. (M. Kornfeld)