THINGS THAT CANNOT TAKE EFFECT TOGETHER [Kidushin: simultaneous]
50b (Mishnah): If one was Mekadesh simultaneously a woman and her daughter, or two sisters, they are not Mekudashos.
(Rava): This is due to Rabah's law.
(Rabah): If either of two things cannot take effect after the other, and they were done simultaneously, neither takes effect.
Question (Abaye - Beraisa): If one separates too much Ma'aser, his Peros are permitted, but the Ma'aser is messed up (some is really Chulin).
According to Rabah, we should say that since one cannot take Ma'aser twice, taking extra Ma'aser at once does nothing!
Answer (Rabah): Ma'aser is different, for it can be taken halfway. One can make half of a fruit Ma'aser. (The proper fraction of every fruit becomes Ma'aser)
Question: (When tithing one's animals, every tenth animal that leaves the pen becomes Ma'aser.) Ma'aser cannot be taken halfway, and it cannot be taken twice, but when two are taken at once, it takes effect!
(Rava): If two animals came out together tenth (and eleventh), one is Ma'aser, and the other is the eleventh (i.e. Chulin).
Answer: Ma'aser Behemah can be taken twice through a mistake.
(Mishnah): If one mistakenly called the ninth 'tenth', and called the tenth 'ninth', and called the 11th 'tenth', all three are Kadosh.
Question: If one tries to be Mekadesh extra (more than 40) loaves with a Korban Todah, some become Kodesh! (Presumably, the Halachah follows Chizkiyah.)
(Chizkiyah): If a Todah was slaughtered with intent to be Mekadesh 80 loaves, 40 of them become Kodesh;
(R. Yochanan): They are not Kodesh.
Answer: R. Zeira explained that if he said that all 80 should become Kodesh, all agree that none become Kodesh. They argue in a case when he did not specify. Chizkiyah holds that the extra breads are in case some of the 40 become Pasul.
Nedarim 69b - Question (Rabah): If he said 'the vow is affirmed and annulled for you at once', what is the law?
Answer: We learn from Rabah's law.
Zevachim 108a (Mishnah - R. Shimon): If someone was Ma'aleh (offered from an animal to idolatry) several times, he is liable for each;
R. Yosi says, he is liable only once.
Temurah 4a (Mishnah): If one said, "The Ma'aseros for basket A are in B, and those for B are in A," A is permitted. (B contains Ma'aser and Tevel.
If he said, "The Ma'aseros for the baskets are in each other," both contain (Ma'aser and) Chulin.
The Rif and Rosh (Nedarim 23b and 10:4) bring the Gemara in Nedarim. The Rosh concludes 'therefore, there is no Kiyum or Hafarah.''
Rambam (Hilchos Ishus 9:1): If one was Mekadesh at once two women, both of them whom cannot be married to him due to Ervah, they are not Mekudashos.
Rambam (Hilchos Nedarim 13:22): If one said to his daughter or wife 'your vow is affirmed and annulled at once', it is affirmed.
Question (Ran DH u'Pashtinan): The Gemara equated this to Kidushin of two sisters. Neither takes effect at all!
Answer #1 (Kiryat Sefer): Since we cannot fulfil both, the first is fulfilled.
Answer #2 (Taz YD 234:38): Since Kiyum was first, surely it is not Batel (by itself). Regarding sisters, even if he said 'Rachel and Leah are Mekudashos to me', 'Mekudashos' refers to both. (We cannot put one first). We prove from sisters only that if one cannot work after the other, they do not work together.
Note: If so, if he said 'Rachel is Mekudeshes to me and Leah is Mekudeshes to me, at once', Rachel is Mekudeshes. I did not find anyone who says so.
Perush ha'Rosh (Nedarim 69b DH Kayam): The question was whether or not we follow the first matter that he said.
Question (Keren Orah, ibid.): If so, how did we learn from Kidushin of sisters?
Tosfos (Zevachim 30a DH Devarav): Rabah's rule applies when both cannot take effect, for they contradict each other. Which would we exclude? In Kidushin 7b, we say that 'I am Mekadesh half of you with a half-Perutah, and half of you with a half-Perutah' does not work (Note: in our text it was not resolved), and ask about 'both halves of you with a Perutah.' Rabah's rule applies only when one prevents the other from taking effect.
Tosfos (Temurah 4a Ma'aseroseihem): If two things cannot take effect one after the other, if they were done at once neither takes effect. Here is different. Since he intends to fix both baskets, it is as if he said 'the Ma'aseros needed for basket A, excluding the part of A needed to become Ma'aser for B, are in B, and those needed for B, excluding the part of B that will be Ma'aser for A, are in A').
Rashba (Kidushin 51a DH v'Abaye): Abaye challenged Rabah. How does Abaye explain the Mishnah? It seems that Abaye accepted Rabah's answer. Or, perhaps Abaye expounds like Rava regarding one who is Mekadesh both sisters (such Kidushin would forbid them Vadai, so it is invalid). He argues only about one who was Mekadesh one of them. This requires investigation.
Pnei Yehoshua (51a DH Abaye): According to what I wrote that the Halachah does not follow Rabah, we must use the Rashba's latter answer. However, why did the Gemara ask why Rava explained the Mishnah like Rabah? If not for Rabah's law, Rava would explain like Abaye! One can resolve this. However, we could say that Abaye holds like Rami bar Chama (to answer the Rashba's question).
Shulchan Aruch (EH 41:2): If one was Mekadesh at once two women that he cannot be married to both due to Ervah, they are not Mekudashos. Neither needs a Get.
Chachmas Shlomo: The Beis Shmuel (2, and Chelkas Mechokek 2 and Taz 1) say that this is because Kidushin does not take effect one after the other. The Rambam (Ma'aseh ha'Korbanos 19:11,12) rules like R. Yosi, who exempts for offering more than once to idolatry, and obligates two who offer to idolatry together. Why don't we say that since it does not apply one after the other, also at once they are exempt?
Note: The Rambam says that "Ish Ish" obligates only when they offer the same limb together. Indeed, he could exempt two who offer different limbs at the same time, which is the 'Bas Achas' case of one after the other!