Gemara

Question (R. Yirmeyah, of R. Zeira): According to R. Meir, who says that an animal born to a woman is a proper child, if a father was Mekadesh such a daughter to a man, what is the law?

Question (R. Zeira): What difference does it make whether or not the Kidushin takes effect?

Answer (R. Yirmeyah): If she is Mekudeshes, her husband is forbidden to her sister.

Inference: She can live!

Objection (R. Zeira): Rav Yehudah taught that R. Meir considers an animal (born to a woman) to be a child only because others of its species live.

Inference: The species lives, but the animal itself cannot live!

(Rav Acha bar Yakov): R. Yirmeyah was merely trying to get R. Zeira to laugh. He failed.

Rishonim

Tosfos (23a DH Le'itsurei): The question did not apply to the daughter herself, to be Mechayev one who has Bi'ah with her, or one who kills her. Surely, she will not live to the age of Bi'ah (three years), or even one year, for she is Terefah.

Rashi (23a DH Lemeimra): We infer that the daughter can live, for after she dies, her husband is permitted to her sister.

Tosfei ha'Rosh (23a DH Lemeimra): This is no proof that she lives. We can say that the Kidushin forbids her mother-in-law. Some obligate (Misah or Kares) for the mother-in-law even after his wife died, and all agree that she is still forbidden. Rather, if she is a Nefel, Kidushin would not take effect.

Ramban (23a DH Lemeimra): According to Rashi, R. Yirmeyah asked a good question. Does the Mekadesh become forbidden to her mother? The Torah forbids a mother-in-law even after the wife dies! Also, he asks whether the Mekadesh is forbidden to the sister for two or three days (until the baby dies). Rather, R. Zeira inferred from the question that the baby can survive. If it could not survive, Kidushin would not take effect on a Nefel, who is totally like a rock. Rav Yehudah taught that R. Meir considers an animal (born to a woman) to be a child only because others of its species live. 'Because' is not precise. Really, R. Meir learns from "Yetzirah-Yetzirah", or because it has Tzuras Adam. Rather, he means that R. Meir considers it a child only regarding Tum'ah, since its species lives, just like a Nefel. A Nefel does not survive, but its species survives.

Ohr Zaru'a (602): Our Sugya (Yevamos 12b) inferred from 'perhaps she will become pregnant and die' that a minor can become pregnant and live. If so, there is a case of a mother-in-law who does Mi'un! I infer that Kidushin takes effect on a Nefel. If not, the Gemara could have rejected 'a mother-in-law cannot do Mi'un. A minor can become pregnant with a Nefel, and she need not die. If she becomes pregnant with a viable baby, she must die. Either way, a mother-in-law cannot do Mi'un.' The Gemara did not say so, for a Nefel can have Kidushin. However, I say that Kidushin does not take effect on a Nefel. Even though we hold like Abaye that Kidushin in which Bi'ah is forbidden are Kidushin, this refers to a live woman who could be a wife. Kidushin does not apply to a piece of flesh. Kidushin applies to a fetus, and one opinion holds that this is even before the fetus is recognized, but the Kidushin is not complete until birth. We can say that our Sugya did not answer like I said, because even if a minor became pregnant with a Nefel, she would die.

Poskim

Rema (EH 37:1): Some say that Kidushin does not take effect on a Nefel.

Chelkas Mechokek (2): The Yerushalmi says that a one-day old girl can become Mekudeshes (even though a baby within 30 days is a Safek Nefel). This is when we know that it was a full-term pregnancy (so she is not a Nefel), or she lived 30 days after the Kidushin, which shows retroactively that she was not a Nefel. It seems that even if she is a Nefel, it is Safek Kidushin, If he was Mekadesh (the baby, and then) her sister, and then her sister's daughter, both of them need a Get due to Safek. The Shulchan Aruch (40:8) brings the Rambam's opinion that Kidushin takes effect even from when the mother is visibly pregnant.

Beis Shmuel (2): Why did the Gemara say that R. Yirmeyah merely tried to make R. Zeira laugh? Perhaps he asked about a man who was Mekadesh such a daughter, and afterwards her sister! It is clear from Tosfos that even though the baby cannot live, i.e. it will not survive, it can live a while. If so, he asked about Kidushin of the sister while the baby was alive. Rather, (since we concluded that R. Yirmeyah had no question, we must say that Kidushin of the baby is void, so) her sister's Kidushin is Vadai valid. This is unlike Chelkas Mechokek, who says that it is a Safek. I discussed a Vadai Nefel. Rashi explained that the question is not relevant, for she will die. Perhaps the Mekadesh was Mekadesh her sister afterwards, while the baby was still alive! Perhaps Rashi holds that the baby does not live at all. [Later, I saw that one can dispel Tosfos' proof. However, one can bring a proof from the questioner. How did he prove from Rav Yehudah's teaching that it does not live even a short time? Perhaps it can live a short time, but since it cannot survive, the mother does not have Tum'as Yoledes. Perhaps Kidushin takes effect while it is alive! Rather, it is clear that Kidushin does not take effect. It is difficult why Rashi did not explain like this.]

Gra (7): The Shulchan Aruch is unlike Rashi. According to Rashi, in any case the question is relevant for other relatives.

Avnei Milu'im (2): The Ramban clearly says that Kidushin does not take effect on a Nefel. The Chelkas Mechokek says that it is Safek Kidushin. His proof from a fetus is invalid, since a fetus is viable. Similarly, a fetus inherits, but a Nefel does not.

Question: When Reuven and David were merry due to wine, Reuven accepted Kidushin from David for when his wife will give birth to a daughter. (His wife was pregnant.) Afterwards, Reuven agreed to marry his older daughter to David. David wants to do the Nisu'in now, before Reuven's wife gives birth. Are we concerned lest she gave birth to a daughter, and Reuven marries his wife's sister, which is an Isur Torah?

Answer (Shevus Yakov 3:118): The Shulchan Aruch (40:8) brings two opinions about this. The Rif and his supporters hold that Kidushin does not take effect on fetuses. The Rambam and his supporters hold that Kidushin takes effect from when the mother is visibly pregnant. Some Acharonim challenged the Rambam, for we hold that one who sells to a fetus or acquires on behalf of a fetsus does not acquire. This is not difficult. Even though one cannot acquire for or transfer ownership of Davar she'Lo Ba l'Olam, one can be Makdish it. In any case it is Safek Kidushin. Really, it is a Sefek-Sefeka (two doubts). Perhaps the fetus is a male. And even if the fetus is a female, Poskim argue about Kidushin of a fetus. Why should we enter a Safek l'Chatchilah? Perhaps the child will be a female, and the latter Kidushin was Batel retroactively according to the Rambam. Even if the child is a Nefel, it is Safek Kidushin according to Chelkas Mechokek. The Beis Shmuel argues, but perhaps the Beis Shmuel is incorrect. What he said in the name of Tosfos is wrong. Tosfos said so only in the Hava Amina. In the conclusion, Rav Yehudah holds that the baby does not live at all, but if it would live, Kidushin would take effect.

Note: Hagahos Ma'ase Nisim (9, in Shulchan Aruch Rosh Pinah) says that the end of the Beis Shmuel [in brackets above] is an addition first printed in the Apei Ravrevei edition (5486). Apparently, Shevus Yakov did not see the addition.

Otzar ha'Poskim (DH Gam): Tif'eres Yakov (3) says that Rashi clearly holds that Kidushin takes effect on a Nefel. He concludes like the Chelkas Mechokek that it is Safek Kidushin. Yad David says that if the Gemara holds that such a baby will never be born alive, there is no proof whether or not Kidushin takes effect on a Nefel. However, perhaps the Gemara holds that the baby (could be born alive but it) cannot survive.

Aruch ha'Shulchan (4): Kidushin cannot take effect on a Nefel. Kidushin can take effect on a baby from when she is born, if we know that she had a full-term pregnancy. If not, it is only Safek Kidushin. There is no Kidushin with a Vadai Nefel, even while it is alive. It is as if it died. If a father accepted Kidushin for a Nefel, and afterwards the Mekadesh was Mekadesh her sister, letter of the law it is Vadai Kidushin. Even so, one should be stringent to require another Kidushin after the Nefel dies, and to forbid Bi'ah until then. I hold that even Rashi agrees. If not, why did R. Yirmeyah ask for mere laughter? He could ask regarding the grandmother! Rather, R. Yirmeyah agrees that a Nefel is not considered alive. He asked about the sister, so R. Zeira would know that he asks only for laughter.