(Beraisa - R. Shimon Ben Gamliel): Any child that lives 30 days is viable (even if he was born in the eighth month, we say that he was a seven month baby that came out late) - "U'Fduyav mi'Ben Chodesh Tifdeh";
Any animal that lives eight days is viable - "Umi'Yom ha'Shemini va'Hal'ah Yeratzeh l'Korban";
Inference: Before these times, it is a Safek.
Question: How may we circumcise [any child] on Shabbos if he is [always] Safek Nefel?
Answer (Rav Ada bar Ahavah): We may circumcise in any case:
If the baby is viable, Milah overrides Shabbos;
If it is a Nefel, it is like cutting dead flesh.
Question (Beraisa): If we are unsure if a baby is seven or eight months, we do not Mechalel Shabbos.
We should be allowed to circumcise in any case - either it is a proper Milah, or like cutting dead flesh!
Answer (Mar brei d'Ravina and Rav Nechumi): Indeed, he may be circumcised on Shabbos - the Beraisa forbids Machshirei Milah, it is like R. Eliezer [who normally permits them].
(Abaye): Tana'im argue about this (whether or not a Nefel is considered dead):
"V'Chi Yamus Min ha'Behemah Asher Hi Lachem l'Ochlah" - this includes an eight month animal, slaughter does not Metaher it [from Tum'as Nevelah. 'Eight month' refers to a premature birth - really, the full term of pregnancy for small Tahor animals is only five months (Bechoros 8A).]
R. Yosi b'Rebbi Yehudah and R. Elazar b'Rebbi Shimon say, slaughter is Metaher it.
Suggestion: Chachamim (the first Tana) consider a Nefel to be alive, R. Yosi and R. Eliezer consider it to be dead.
Rejection (Rava): If so, instead of arguing about Tum'ah, they should argue about eating it!
Rather, all agree that it is dead; R. Yosi and R. Elazar consider it like a Treifah - even though it is dead, slaughter is Metaher it - the same applies to a Nefel;
Chachamim do not consider it like a Treifah - a Treifah was once fit to live, a Nefel was never fit to live.
Question: An animal born Treifah was never fit to live [yet slaughter is Metaher it]!
Answer: Slaughter applies to the category of Treifos, but not to the category of Nefalim.
Question #1: Do Chachamim argue with R. Shimon ben Gamliel?
Question #2: If you will say that Chachamim argue with him - does the Halachah follow him? (The following two answers are to Question #1, i.e. there is a Tana who is not concerned for a Nefel within eight days, unlike R. Shimon.)
Answer #1 (Beraisa): A calf born on Yom Tov may be slaughtered that same day.
Rejection: The case is, we know that it had a full term pregnancy.
Answer #2 (Beraisa): All agree that if a Bechor was born blemished [on Yom Tov], it is Muchan (it may be slaughtered that day).
Rejection: Here also, we know that it had a full term pregnancy.
Answer #3 (to both questions): Rav Yehudah taught that the Halachah follows R. Shimon.
This implies that they argue!
(Abaye): If a baby (within 30 days) fell from the roof or was eaten by a lion, all agree that he was [Muchzak to be] alive (most babies are not Nefalim);
They argue about when he yawned and died [soon after birth, before showing any sign of strength].
Question: What difference does it make whether or not he was a Nefel?
Answer: If he was alive (and his father died before him without other descendants), he exempts his mother from Yibum.
Objection: They argue about a baby who fell from the roof or was eaten by a lion!
Rav Papa and Rav Huna brei d'Rav Yehoshua visited Rav Idi bar Avin; he prepared for them a third-born calf (it is healthiest) on its seventh day; they told him, had you waited until evening (its eighth day) to slaughter it, we would have eaten it - since you slaughtered it now, we will not eat it.
Correction: Rather, if he yawned and died [soon after birth], all assume that he was a Nefel;
They argue about a baby (within 30 days) who fell from the roof or was eaten by a lion - R. Shimon assumes that he was a Nefel, Chachamim assume that he was alive.
SAFEK NEFEL (cont.)
Rav Dimi bar Yosef's son had a son that died within 30 days - the father was mourning over him.
Rav Dimi: Do you seek to eat the nice foods brought to mourners?! (We do not mourn over Nefalim!)
His son: I know that he was a nine month baby (not a Nefel).
Rav Ashi visited the house of Rav Kahana; Rav Kahana's son had died within 30 days, he was mourning over him.
Rav Ashi: Rav Yehudah taught that the Halachah follows R. Shimon!
Rav Kahana: I know that he was a nine month baby.
(Ravina citing Rava): If [a man died leaving only one child, and] the child died within 30 days, and the widow became Mekudeshes (if the baby was a Nefel, Yibum or Chalitzah is required):
If a Yisrael (who may marry a Chalutzah) was Mekadesh her, she does Chalitzah;
If a Kohen was Mekadesh her, she does not do Chalitzah (Tosfos - regarding Eshes Kohen the Halachah follows Chachamim, we assume that the baby was viable).
(Rav Sharbiya citing Rava): In either case, she does Chalitzah.
Ravina: Rava said so at night, but the next morning he retracted [and said like I reported]!
Rav Sharbiya: If only you would permit Chelev!
(Mishnah - R. Yehudah): We may circumcise an Androginus on Shabbos.
(Rav Shizbi): R. Yehudah does not consider an Androginus to be male in every respect - if so, he would have an Erech! (If one says 'Erech Ploni Alai', this obligates him to give to Hekdesh a certain amount based on Ploni's age and gender.)
Question: How do we know that an Androginus has no Erech?
Answer (Beraisa): "[V'Hayah Erkecha] ha'Zachar" - this excludes a Tumtum or Androginus.
Suggestion: Perhaps this teaches that Erech of a male does not apply to them, rather, Erech Nekevah!
Rejection: "V'Hayah Erkecha ha'Zachar...v'Im Nekevah Hi" - Erchin applies to a Vadai male or female, not to a Tumtum or Androginus.
A Stam (anonymous) Sifra (Beraisa that expounds a verse in Vayikra) is R. Yehudah!
Support (Rav Nachman bar Yitzchak - Mishnah): Everyone is Kosher to Mekadesh (mix ashes of the Parah Adumah with the water), except for a child, lunatic or deaf person;
R. Yehudah is Machshir a child, he is Posel a woman and Androginus.
This shows that he does not consider an Androginus a male for other laws.
Question: Why is Milah different?
Answer: "Himol Lachem Kol Zachar" includes an Androginus.