DO WE RELY ON BREIRAH? [Bereirah]
We have another source that R. Yehudah [and R. Yosi and R. Shimon] hold that Ein Breirah:
(Beraisa #1 - R. Meir): If one bought [100 Lugim of] wine from Kusim [and lacks Kelim into which to put the tithes], he says 'the two Lugim that I will separate later should be Terumah. Ten Lugim [that I will separate] are Ma'aser Rishon, and nine Lugim are Ma'aser Sheni.' He [redeems the Ma'aser Sheni and] may drink immediately;
R. Yehudah, R. Yosi and R. Shimon forbid.
37b (Rav Yosef): Tana'im argue about [whether or not Yesh Breirah];
(Beraisa): If one said 'I will be Me'arev for every Shabbos of the year that I will want to go', if he decided before Shabbos, the Eruv is valid for that Shabbos;
R. Shimon says, [even] if he decided after dark it is valid;
Chachamim say, in this case it is invalid.
Question: R. Shimon contradicts himself. Elsewhere (Beraisa #1), he holds that Ein Breirah!
Answer #1: The opinions in the Beraisa must be switched.
Question: Why must we switch the opinions? Perhaps R. Shimon holds that Yesh Breirah for mid'Rabanan laws, but Ein Breirah for mid'Oraisa laws!
Answer: Rav Yosef holds that the Tana'im do not distinguish between mid'Oraisa and mid'Rabanan regarding Breirah.
Answer #2: Normally, they (R. Yehudah, R. Yosi and R. Shimon) hold that Yesh Breirah. Terumah is different, for "Reishis [Deganecha...]" teaches that the remnants after taking Reishis (Terumah) must be recognizable [at the time of separation].
Answer #3: A Beraisa teaches that they agree that Yesh Breirah. (They forbid for a different reason);
(Beraisa - R. Yehudah, R. Yosi and R. Shimon, to R. Meir): Aren't you concerned lest the barrel break, and retroactively he drank Tevel [for he will never be able to separate the tithes]?
R. Meir: Until it breaks, we are not concerned.
Beitzah 37b (Rav): If Reuven and Shimon jointly bought (before Yom Tov) a barrel (of wine) and an animal, and they have different Techumim, the barrel is permitted (each may take his share whenever he may go) and the animal is forbidden (outside of the overlap of their Techumim);
(Shmuel): Both (the barrel and animal) are forbidden.
Question: If Rav holds that Yesh Breirah, he should permit both of them (it is as if Reuven's share was his from the start on Yom Tov, so it received his Techum). If he holds that Ein Breirah, he should forbid both of them! (Perhaps Reuven took Shimon's share, and it received Shimon's Techum.)
Answer: Really, he holds that Yesh Breirah. An animal is different, for Reuven's share nourished from (Shimon's, which has) a different Techum, and vice-versa.
Question (Rav Kahana and Rav Asi): If we are not concerned for (nourishment from the other's share, which is) Muktzah, all the more so we are not concerned for (nourishment from other) Techumim!
Rav did not answer.
38a - Question: What was the conclusion?
Answer: R. Yirmeyah holds that Ein Breirah, and R. Oshaya holds that Yesh Breirah, i.e. for mid'Rabanan laws. For Torah laws, Yesh Bereirah.
The Halachah follows R. Oshaya.
9a (Shmuel): Chalah of Chutz la'Aretz - one may eat [the bread], and afterwards he separates [Chalah].
Rif: Rav holds that Yesh Breirah, but not for an animal. Since the limbs nourish from each other, it is as if the Techumim are mixed. Shmuel holds that Ein Breirah in all cases. We conclude like R. Oshaya, that for mid'Rabanan laws Yesh Breirah. This is like Rav, so the Halachah follows Rav.
Rebuttal (Ba'al ha'Ma'or): Rashi explains that only Rav is concerned for nourishment of one part of the animal from the rest. R. Oshaya holds that Yesh Breirah for mid'Rabanan laws, both for a barrel and an animal. Rav was challenged by Rav Kahana and Rav Asi, and he was unable to answer, so the Halachah does not follow Rav.
Defense (of Rif - Milchamos Hash-m): R. Oshaya is concerned for nourishment of one part of the animal from the rest, just like Rav. Rav's silence was not admission; he saw no need to answer them!
Rebuttal (Ran DH Tanu Rabanan): Rav Kahana and Rav Asi were Talmidei Chaverim of Rav. He would not have ignored their question if he had an answer!
Rambam (Hilchos Yom Tov 5:20): If Reuven and Shimon jointly bought an animal, and divided it on Yom Tov, all the meat is permitted only in the overlap of their Techumim. Regarding a barrel, each may take his share wherever he may go. Since Techumim is mid'Rabanan, Yesh Breirah. For an animal, each share nourished from the other; every limb contains parts of both shares.
Rosh (5:7): The Gemara asked (what was the conclusion?) about an animal, for Rav did not answer the question of Rav Kahana and Rav Asi. If the question was about Breirah, we know the general rule that the Halachah follows Rav against Shmuel in Isurim! The Gemara did not say that the Halachah follows Rav. This shows that R. Oshaya disagrees with Rav; even an animal is permitted.
Mahari Veil (48): If Chalah was not separated from a dough and it was cooked, there is a solution to take Chalah afterwards. Even though it was all Tevel when it was cooked, since he separated afterwards, we say Bereirah for mid'Rabanan laws. This is why we hold that Chalah of Chutz la'Aretz, one may eat, and afterwards he separates.
Rebuttal (Chacham Tzvi 9 DH Mah she'Chasav): You cannot say that it is retroactively clarified that it is as if he separated before. Declaration of Chalah depends on the owner's intent. Since he did not intend to separate now, how can it be Chalah retroactively?!
Defense (Yad Sha'ul, on Taz YD 323:5): He wants it to take effect now, for one must separate Min ha'Mukaf (near the dough that is exempted)! Also, there is an Isur to eat Tevel (before separation)! Regarding a Mitzvah, we say that anything destined, it is as if it already happened (Tosfos Sotah 25b DH Lav).
Note: It seems to me that Tosfos says that R. Shimon said that anything destined [e.g. to be thrown], it is as if it already happened, only for Mitzvos, but in most cases Rabanan argue!
Shevet ha'Levi (4:148 DH Ela): Shmuel holds (Beitzah 37b) that Ein Bereirah! However, we can say that Chalas Chutz la'Aretz is very lenient, so even according to the opinion that Ein Bereirah for mid'Rabanan laws, Bereirah helps for it. Toras ha'Aretz brings from Chalas Lechem that Chachamim stipulated that one may eat and separate afterwards.
Shulchan Aruch (OC 32:8): The parchment [for Tefilin] must be tanned Lishmah. It is good to say with his lips at the beginning of the tanning that he tans for Tefilin or a Sefer Torah. If he tanned it for a Mezuzah, it is Pasul.
Mishnah Berurah (27): When he puts the hide in lime, he should say "l'Shem Kedushas Sefer Torah, and I stipulate that when I want, I may use it for anything", and unlike the custom of scribes who say "l'Shem Sefer Torah or Tefilin or Mezuzah any other matter of Reshus." In such a case, the Acharonim are unsure if it helps.
Bi'ur Halachah (DH Oh): This is because for Torah laws, we hold like Ein Bereirah. According to what the Pri Megadim wrote that tanning Lishmah is mid'Rabanan, one may be lenient b'Di'eved. This requires investigation in practice.
Teshuvos v'Hanhagos (2:15): Also the Tenai that the Mishnah Berurah advocates is not unanimous. R. Nasan Adler said that if one stipulates that he may be Mevatel a fast when he will want, his acceptance is lacking, and it does not help. Also here the Lishmah is lacking, since he can be Mevatel it when he wants. Also Oneg Yom Tov (6) was unsure about this. If one stipulated "what I cut off will not get Kedushah", this does not depend on Bereirah, because it is b'Yado.
Shulchan Aruch (153:15): One cannot forbid [to others] his share in the Beis ha'Keneses, and not from Seforim. If he forbade, it has no effect.
Beis Yosef (DH Kasuv b'Sefer): Orchos Chayim brings so from the Ra'avad and all Chachamim of his generation.
Mishnah Berurah (87): The Ge'onim enacted so. If not, anyone who has a quarrel with his friend will forbid his share to him, and automatically the entire Beis ha'Keneses is forbidden to him, for Ein Bereirah.
Magen Avraham (38): Hagahos Maimoniyos brings that if one forbade his share of the Ma'aser money of the Tzibur, R. Shimshon permitted them. Maharshal said that people give Ma'aser with intent that the leaders of the city use it as they see fit, so one cannot forbid it. It is unlike the Beis ha'Keneses, which everyone has his rights in it. I say that Ma'aser is not considered his.
Kaf ha'Chayim (129): Eliyahu Rabah says that also this (one cannot forbid the Tzibur's Ma'aser) is due to the enactment.
Bi'ur Halachah (DH Ein): it seems that this is only if he did not have a fixed place, rather, the Beis ha'Keneses is jointly owned. According to the custom that everyone buys a fixed place, and he can bequeath or sell it, perhaps this does not apply. The Me'iri says that many Poskim hold that in any case he cannot forbid, but he leans to say like I said.
Bi'ur Halachah (DH Eino): This is an enactment, i.e. according to the first opinion in YD 224. According to the other opinion, anything without a law [that one can force his partner] to divide, according to letter of the law one cannot forbid his friend\; the same applies here. The Shach there leans to say that the latter opinion is primary.
Shulchan Aruch (OC 397:10): If Reuven and Shimon jointly bought an animal, and slaughtered and divided it on Yom Tov, all the meat is permitted only in the overlap of their Techumim.
Beis Yosef (DH Shnayim): We follow the Rif and Rambam against the Rosh.
Bi'ur Halachah (DH Harei): Most Rishonim hold like the Rosh. Therefore, one may be lenient if there is a great need.
Shulchan Aruch (ibid.): However, if they bought a barrel and divided it on Yom Tov, each may take his share wherever he may go.
Mishnah Berurah (24): For mid'Rabanan laws Yesh Bereirah, so it is as if they divided before Yom Tov. Regarding an animal, Bein ha'Shemashos each share nourished from (the other share, which has) a different Techum, so it is as if they did not divide.
Shulchan Aruch (448:1): Chametz of a Nochri that Pesach passed over it, one may even eat it.
Mishnah Berurah (2): If a Yisrael was a partner with a Nochri in Chametz and Pesach passed and afterwards they divided, he may benefit from the Nochri's share, for Yesh Bereirah for mid'Rabanan laws, and retroactively it is clarified it was the Nochri's. The same applies if two Yisraelim were partners in Chametz and one of them sold his share to a Nochri. The share he takes later is permitted, and the other's share is forbidden.
Kaf ha'Chayim (3): This requires investigation whether one may eat the Nochri's share. Chukas ha'Pesach and R. Zalman permit. Sha'agas Aryeh permits even the Yisrael's share. Zera Emes permits relying on this to benefit from it if otherwise there will be a big loss.
Shulchan Aruch (YD 323:1): One may eat and afterwards separate Chalah of Chutz la'Aretz, since it is mid'Rabanan.