How can Ula say that "everyone agrees to this," referring to Rav and Shmuel?
In the Gemara earlier (73a), Shmuel says clearly that in a case where one
performed Kidushin with a Tenai and then performed Nesu'in without
specifying any Tenai, the woman is *not* considered married and she does
*not* need a Get!
In addition, Shmuel there says that if a woman -- who was married off by her
mother or brothers when she was a Ketanah -- marries someone else after she
reaches the age of adulthood, she is considered married to the second man
and needs a Get, since she was never married mid'Oraisa to the first
husband, even though he lived with her after she became an adult. Obviously,
Shmuel does not agree that "Ein Adam Oseh Be'ilaso Be'ilas Z'nus!" How,
then, could Ula say that "everyone agrees?"
(a) TOSFOS (DH Divrei ha'Kol) explains that according to Ula, what Shmuel
meant is not that a Be'ilah after the Tenai does not override the Tenai.
Rather, the Be'ilah afterwards certainly overrides the Tenai, because "Ein
Adam Oseh Be'ilaso Be'ilas Z'nus." Shmuel is discussing a case where the man
did Nesu'in *without* Be'ilah; he did Nesu'in with Chupah alone. That is why
the Tenai still remains -- for there is no Be'ilah.
If the man did not do Nesu'in with Be'ilah but only with Chupah, why, then,
does Rav say that she needs a Get, if there was no Be'ilah? The answer is
that Rav holds that by making a Nesu'in with Chupah, the husband shows that
he is willing to forego the Tenai (since be obviously plans to have Bi'ah
with her during Nesu'in, and he does not want it to be a Bi'as Z'nus), and
therefore the *original* Kidushin now takes effect.
Why does Shmuel say that the Kidushin of a Ketanah (who later did Mi'un)
does not become d'Oraisa after the husband lives with her when she reaches
adulthood? Tosfos explains (based on the Gemara in Yevamos 110a) that in the
case of a Ketanah the Be'ilah is not really a Be'ilas Z'nus because there
does exist a Kidushin mid'Rabanan. That is why Shmuel says that the Be'ilah
during adulthood does not effect a Kidushin. But in a case where the man was
Mekadesh the woman with less than a Perutah and then did Bi'ah with her, the
Bi'ah does make a Kidushin, because "Ein Adam Oseh Be'ilaso Be'ilas Z'nus."
(b) The RITVA, after addressing the other possibility, concludes that there
is a printing error in our Gemara and the words "Divrei ha'Kol" ("everyone
agrees") should be omitted. Accordingly, Ula is expressing only the opinion
of Rav and not the opinion of Shmuel.
The practical difference between these two approaches is what happens when
the man performs Nesu'in (Chupah) without doing Be'ilah with her. According
to Tosfos, the Halachah follows Rav and Chupah alone without Be'ilah *does*
serve to make them married, because the man foregoes the Tenai with Chupah
alone (see Shulchan Aruch EH 38:35). According to the Ritva and other
Rishonim, only after doing Be'ilah does the Kidushin take effect, since "Ein
Adam Oseh Be'ilaso Be'ilas Z'nus."
The BEIS SHMUEL (EH 38:59) adds that there is another practical difference.
According to Tosfos, it should not be necessary to have witnesses at the
time of the Chupah or Be'ilah, since the Kidushin was performed earlier with
witnesses and now he is just foregoing the Tenai and not making a new
Kidushin. (This is indeed how the RAMBAM rules). According to those who say
that the only reason the Kidushin takes effect is because he performs a new
act of Kidushin (without a Tenai) by doing Be'ilah and "Ein Adam Oseh
Be'ilaso Be'ilas Z'nus," then there must be witnesses at the time of the
Be'ilah in order for the new Kidushin to take effect, because Kidushin takes
effect only with witnesses (this is how the ROSH rules).
The AVNEI MILU'IM suggests that this practical difference of the Beis Shmuel
is not necessarily correct. Rather, even according to Tosfos, it could be
that witnesses are necessary for the Nesu'in. Even though the Kidushin has
already been performed and now the husband is just annulling the Tenai (with
the Chupah or Be'ilah), nevertheless, he is only annulling the Tenai in
order for the subsequent Be'ilah not to be a Be'ilas Z'nus. To accomplish
this, the Chupah must be a proper act of Nesu'in. Nesu'in, the Avnei Milu'im
posits, should be considered a "Davar she'b'Ervah" since it affects her with
regard to certain Halachos (such as whether her punishment for adultery will
be Sekilah or Chenek, if she is a Na'arah Me'urasah, and such as becoming
Tamei for her if she dies, if he is a Kohen). Therefore, as we find with
Kidushin (Kidushin 66b), if there are no witnesses present that Chupah or
Bi'ah will not accomplish Nesu'in, and the subsequent Be'ilah will be a
Be'ilas Z'nus in any case. If so, threre is no reason to assume that the man
is foregoing the Tenai with this Chupah or Bi'ah.
(The Avnei Milu'im's assertion that Nesu'in requires the presence of
witnesses in order for it to take effect is debated by the other Acharonim.
Although the TOSFOS RI HA'ZAKEN (a.k.a. Rav Shlomo Min ha'Har) in Kidushin
10b does seem to require the presence of witnesses for Nesu'in to take
effect, as the Avnei Milu'im writes, the AVNEI NEZER (EH 395) and MARCHESHES
(2:1:7) point out that the RAMBAM (Hilchos Ishus 7:23) seems to rule
otherwise. The CHELKAS YO'AV (EH 6) proves that the ROSH (Bava Basra 9:16)
also does not require witnesses for Nesu'in to take effect. See also OR
SAME'ACH to Hilchos Ishus 10:2.)