99b (Beraisa - R. Yehudah): Aninus (one who lost a relative may not eat Kodshim) at night is mid'Oraisa;

R. Shimon says, it is only mid'Rabanan.

R. Shimon: Surely I am right. Chachamim taught that an Onen immerses and eats Pesach at night, but not other Kodshim!

(Rav Mari): If the death and burial of the relative were on the 14th, the Onen does not bring Pesach. for Aninus applies mid'Oraisa to the night following death;

If the death was on the 13th and burial was on the 14th, he brings Pesach. for Aninus applies only mid'Rabanan to the night following burial.

100b (Beraisa - R. Yehudah): "Hen ha'Yom Hikrivu" - the Kodshim of the Milu'im (to inaugurate the Mishkan) were forbidden (to Onenim) during the day and permitted the next night. After this (i.e. for all generations), Kodshim are forbidden (to Onenim) during the day and the next night;

Rebbi says, Aninus at night is only mid'Rabanan.

101a: Aharon answered Moshe "...v'Achalti Chatas ha'Yom ha'Yitav b'Einei Hash-m" - perhaps Hash-m commanded only to eat Kodshei Sha'ah in Aninus.

Mo'ed Katan 14b: Aveilus does not apply during the Mo'ed because it says "v'Samachta b'Chagecha". If one was an Avel before the Regel, the Aseh (of the Regel) of the Rabim overrides the Aseh of an individual. If he became an Avel during the Regel, the Aseh of an individual does not override the Aseh of the Rabim.

Kesuvos 3b (Beraisa): If the bread was baked, the animals were slaughtered, or the wine was mixed, and then the Chasan's father or bride's mother died:

We put the deceased in a room until after the Chupah... They have Bi'as Mitzvah, and separate. They celebrate the seven days of Mishteh (nuptial festivities), followed by seven days of Aveilus.

Berachos 16b (Mishnah): R. Gamliel bathed on the night after his wife died.

R. Gamliel holds that Aveilus on the night after death is only mid'Rabanan - "va'Acharisah k'Yom Mar" (mid'Oraisa, it is only during the day). Chachamim did not decree to forbid an Istenis (one who is pained if he cannot bathe).

Bechoros 49a (Shmuel): In Aveilus, the Halachah always follows the lenient opinion.

Rif (Berachos 9b): Some say that the seven days of Avelus are mid'Oraisa. They learn from "va'Ya'as l'Aviv Evel Shiv'as Yomim". This is wrong. The Gemara in Zevachim say that it is only mid'Rabanan. Only R. Yehudah holds that Aveilus of the first night is mid'Oraisa. The Halachah follows the other Tana'im. The Asmachta for seven days of Avelus is "v'Hafachti Chageichem l'Evel". Just like the Chag is seven days, also Aveilus.

Question: The Gemara in Mo'ed Katan calls Aveilus an Aseh (mid'Oraisa) of an individual, even after the first day!

Answer #1 (Rif): The Gemara says that even according to the opinion that Aveilus of the first night is mid'Oraisa, it does not override the Regel.

Rebuttal (Ra'avad, brought in Rosh Mo'ed Katan 3:3): It is unreasonable that the Stam Gemara is unlike the Halachah.

Answer #2 (Ra'avad): The Aveilus of Sheloshim (30 days), which forbids laundering and haircuts, is mid'Oraisa. We learn about haircuts from a Hekesh to Nazir (19b), and laundering is equated to haircuts.

Rebuttal (Rabeinu Meir, brought in Rosh Mo'ed Katan 3:3): One who transgresses these matters of Aveilus is Chayav Misah (b'Yedei Shomayim) (Mo'ed Katan 19b). If this were mid'Oraisa, it should have been listed with all the Chayavei Misos in Sanhedrin 83a! It is difficult to say that the Tana omitted some, for it says 'Elu'!

Answer #3 (Rabbeinu Meir): Rather, it is only mid'Rabanan. The Misah is for (transgressing a mid'Rabanan -) "u'Foretz Gader Yishcenu Nachash."

Rif (Mo'ed Katan 11b) If a Mes died and was buried on Yom Tov Sheni of Chutz la'Aretz at the end of the Regel or Shavu'os, since Yom Tov Sheni is mid'Rabanan and the first day of Aveilus is mid'Oraisa, an individual's Aseh mid'Oraisa overrides the Aseh mid'Rabanan.

Rosh (ibid.): BaHaG says similarly. He calls Yom Tov Sheni a Safek mid'Rabanan. The Gemara (Mo'ed Katan 14b) says Stam that Aveilus is mid'Rabanan, i.e. always, even on the day of burial. Rashi says that the Isur Melachah is mid'Rabanan. "V'Hafachti Chageichem l'Evel" is an Asmachta. However, what we learn from Yechezkeil ("He'anek Dom...") is mid'Oraisa. It exempts an Avel even from Tefilin, which is mid'Oraisa.

Rebuttal (Rosh): This is not a proof. If we learned from Yechezkeil, we would exempt from Tefilin all seven days, like everything else learned from Yechezkeil. An Avel is exempt from Tefilin only on the first day, because it is called "Pe'er".

Rambam (Hilchos Evel 1:1): Aveilus is mid'Oraisa only on the first day when it is the day of burial. The rest of Shivah (the seven days of Aveilus) is only mid'Rabanan. Moshe enacted that Yisrael observe seven days of Aveilus and seven days of Mishteh (for a Chasan).

Rambam (2:1): The Torah obligates Aveilus over a parent, child, and paternal sibling. Mi'Divrei Sofrim one mourns over his full (Nesu'ah) wife or husband, and maternal sibling.

Rambam (10:9): In places where two days of Yom Tov are observed, we count Shiv'ah from Yom Tov Sheni ha'Acharon (at the end of the festival). Even though he does not conduct Aveilus that day, since it is mid'Rabanan it counts towards Shiv'ah. He counts only six days after it. He counts Sheloshim from the day of burial.

Rambam (10): If one buried his Mes on Yom Tov Sheni ha'Acharon, or on Yom Tov Sheni of Shavu'os, since Yom Tov Sheni is mid'Rabanan, and the first day of Aveilus is mid'Oraisa, the Torah Aseh (Aveilus) overrides the Aseh mid'Rabanan (Yom Tov Sheni). However, if he buried on Yom Tov Sheni of Rosh Hashanah, he does not conduct Aveilus, for both days are considered like a long day.

Rosh (Kesuvos 1:5): The Ramah says that the first day of Mishteh is mid'Oraisa; we learn from "b'Yom Chasunaso uv'Yom Simchas Libo". Therefore it overrides Aveilus. Some say that BaHaG did not mean that Aveilus of the first day is mid'Oraisa. Rather, since it has an Asmachta ("va'Acharisah k'Yom Mar"), and Yom Tov Sheni is a mere custom, Aveilus overrides.

Rosh (Mo'ed Katan 3:27): If one buried his Mes during the festival, Aveilus applies only after the festival. He counts Shiv'ah from Yom Tov ha'Acharon. Even though he does not conduct Aveilus that day, it counts towards Shiv'ah. He counts only six days after it. If a Mes died on Yom Tov Sheni ha'Acharon, or on Yom Tov Sheni of Shavu'os, he conducts Aveilus, for it is the day of death and burial. Rabanan agreed that the first day of Aveilus is mid'Oraisa - "v'Achalti Chatas ha'Yom", "va'Acharisah k'Yom Mar." An individual's Torah Aseh overrides the Aseh mid'Rabanan of the Rabim. If so, we must distinguish and say that if a maternal brother or married sister died on Yom Tov Sheni, he does not mourn that day, for an Aseh mid'Rabanan of an individual does not override an Aseh of the Rabim. These are the words of early Chachamim. Acharonim decided that there is no Aveilus mid'Oraisa, even the first day. Only Aninus is mid'Oraisa. Their proofs are clear; do not veer from them.

Shulchan Aruch (OC 548:3): If a Mes died and was buried on Yom Tov Sheni of Chutz la'Aretz at the end of the Regel, since Yom Tov Sheni is mid'Rabanan and the first day of Aveilus is mid'Oraisa, Aveilus overrides Yom Tov Sheni.

Beis Yosef (DH v'Chosav ha'Rosh): In YD 399, the Tur said that all the Ge'onim hold like Bahag. The Ramban adds that the Ge'onim discuss only the seven relatives explicit in the Torah. We do not mourn on Yom Tov Sheni over those that Chachamim added. Some say that we do not mourn at all on Yom Tov Sheni of Rosh Hashanah, for it is one Kedushah. Even though he does not conduct Aveilus, it counts (towards Shiv'ah). The Ramban holds like the Ge'onim, that since it is mid'Rabanan, Aveilus mid'Oraisa overrides it. The Rashba says that the Ge'onim discuss only when Yom Tov ha'Acharon is the day of death and burial, but not if death was on Yom Tov Rishon and burial was on Yom Tov Sheni. Bahag and the Rif connote like this. He brought a proof from Kesuvos 3b, in which we say that if the food was ready, and the Chasan's father or bride's mother died, we put the deceased in a room, (they have Bi'as Mitzvah,) and it is not buried until the next day (and they celebrate the seven days of Mishteh, followed by seven days of Aveilus). If Aveilus of the day of death alone (not the day of burial) were mid'Oraisa, how could we permit Bi'as Mitzvah?! If Aveilus of the day of burial alone were mid'Oraisa, how could we permit seven days of Mishteh including the day of burial? The days of Mishteh are no stronger than Yom Tov Sheni! We explicitly say in Zevachim that if death and burial were both on the 14th, Aninus is mid'Oraisa. If the death was on the 13th and burial was on the 14th, the day of burial is only mid'Rabanan.

Rema: Some disagree and hold that there is no Aveilus on any Yom Tov Sheni. This is the custom; one should not deviate.

Beis Yosef (DH u'Mah she'Chosav): R. Tam says that even if he died on Yom Tov Sheni, there is no Aveilus that day. The Rosh agreed with this, and the Tur ruled like this in YD (399), but he did not protest against those who conducted like the Ge'onim. R. Yerucham says that Bahag is primary, and this is proper, for the Rif and Rambam agree.

Gra (DH v'Aveilus): The Rif holds that the first day of Aveilus is mid'Oraisa, but even the first night (afterwards) is mid'Rabanan. R. Gamliel says so in Berachos, and R. Shimon and Rebbi say is in Zevachim. R. Yehudah holds that it is mid'Oraisa, but only when it is the day of death and burial.

Gra (DH v'Yesh): The latter opinion holds that only Aninus is mid'Oraisa, regarding eating Kodshim. In Berachos we say that since the night is mid'Rabanan regarding Kodshim, we are lenient also about Aveilus. In Aveilus, the Halachah always follows the lenient opinion. If it were mid'Oraisa, we would be stringent! The leniencies of Aveilus are because it is mid'Rabanan. We say 'an Aseh... overrides...', i.e. an Aseh mid'Rabanan, just like we say (Pesachim 84a) 'Shabaton is an Aseh...', even though it is only Shevus (mid'Rabanan), and that a Tevul Yom who enters Machaneh Levi transgresses an Aseh, even though it is only mid'Rabanan.

Mishnah Berurah (11): Yom Tov Sheni ha'Rishon is no less than Chol ha'Mo'ed (so Aveilus does not override it).

Mishnah Berurah (13): The Torah commanded even Kohanim to become Tamei for their relatives, and all the more so Yisre'elim, lest they refrain from mourning over them. This shows that Aveilus of the first day is mid'Oraisa.

Kaf ha'Chayim (14, citing the Bach): If one comes to conduct like the Ge'onim, we protest due to "Lo Sisgodedu (do not make factions)", for we already accepted to conduct like R. Tam and the Rosh.