Gemara

(Mishnah): There is no Kares for eating Kutach of Bavel (a dip made with stale bread) during Pesach.

44a (Rav Dimi): This is because one does not normally eat a k'Zayis [of Chametz] in the time to eat a half-loaf;

If he eats it straight, Batlah Daito Etzel Kol Adam (the law is based on normal practice);

If he eats it like a dip, he will not eat a k'Zayis within the time!

Eruvin 28a: Before Rav came to Bavel, he forbade to use immature grain (fodder) for an Eruv. After he came [and saw that people eat it], he permitted it.

Question: Bavel is not the majority of the world!

(Beraisa): If one planted beans or barley to eat the vegetable, Batlah Daito Etzel Kol Adam. The seeds are Tevel, and the vegetable is exempt.

Shabbos 92a (Rav): If one was Motzi on his head he is liable, for this is how people in Hutzal carry.

Objection: Is Hutzal the majority of the world?!

Correction: Rather, if one from Hutzal was Motzi on his head he is liable, for this is how people in his city carry.

Objection: Batlah Daito Etzel Kol Adam!

Correction: Rather, if one was Motzi on his head he is exempt. Even though people in Hutzal carry this way, Batlah Daitam.

144b (Beraisa): In the house of Menasiya bar Menachem they would squeeze pomegranates.

(Rav Nachman): The Halachah follows [the Tana who forbids squeezing pomegranates, for he holds like] Menasiya.

Objection: Menasiya is not the majority of the world!

Answer: Indeed, we find that practices in one region determine the Halachah everywhere!

(Mishnah - R. Elazar): If one lets thorns grow in a vineyard, this is Kil'ayim. The thorns and nearby vines are forbidden;

Chachamim say, only something that people normally grow is Kil'ayim.

(R. Chanina): R. Elazar forbids thorns because in Araviya people grow cactus for their camels.

Rejection: Araviya is a whole region. Menasiya is an individual. His opinion is Batel to that of normal people.

Kidushin 6a (Beraisa): If he says 'you are Charufasi' she is Mekudeshes, for in Yehudah, an Arusah is called Charufah.

Question: Is Yehudah the majority of the world?!

Answer: In Yehudah, if one said 'you are Charufasi', she is Mekudeshes...

Rishonim

Hagahos Ashri (Avodah Zarah 2:34): The Rashbam rules like R. Yochanan, who said that salting is cooking. Since we do not eat herring raw, it is permitted to us [even if a Nochri salted it]. It is forbidden to one who eats it raw.

Ritva (28a DH Batlah): Batlah Daito Etzel Kol Adam, so he does not tithe the Yerek at all. He tithes only the seeds, for in the entire world they are planted primarily for the seeds. Why did the Gemara ask from a person to a region? In Shabbos (144b), we say that we cannot learn from R. Eliezer, who forbids thorns because in Araviya people keep them for camels, to rule like an individual regarding pomegranates. I answer that the case of thorns is different. Even though they do not do so elsewhere, it is not abnormal. Surely they are good for camels, just elsewhere they do not have camels. This is why R. Eliezer considers Araviya like the majority of the world. Rabanan disagree, but they agree that in Araviya, thorns forbid. However, a bizarre, illogical and improper custom is not a custom. Even where they do so, Batlah Daitam Etzel Kol Adam (Shabbos 92b). Planting grain for fodder is like carrying on the head in Hutzal. It is improper. Even if an entire region does so, Batlah Daitam even for themselves. This is why we asked that Bavel is not the majority of the world, that others should be drawn after their custom. Just the contrary! Since their custom is strange, it is not a custom even for them.

Question (Ritva): How do we bring a proof about pomegranates from thorns? Rabanan do not learn from Araviya!

Answer (Ritva): [Rav Nachman] holds that the Halachah follows R. Eliezer. Alternatively, he holds that there Rabanan argue, for they hold that even though guarding thorns is not strange, it is not a totally good custom, for sometimes the loss exceeds the gain. Elsewhere, people have camels, and they do not guard thorns! Squeezing pomegranates is a proper custom. It is better for Refu'ah and food. Elsewhere they do not do so because pomegranates are not plentiful. Therefore, Rabanan agree that they are like the majority of the world. Even so, we answer that there is different, for Araviya is a region. Pomegranates is the custom of Beis Menachem, i.e. a man. We infer that whenever a region [have a custom], they are like the majority of the world.

Question: If one said 'you are Charufasi', she is Mekudeshes only in Yehudah, where an Arusah is called Charufah, but not elsewhere! This is like the Gemara asked, is Yehudah the majority of the world?!

Answer (Ritva): Charufah is an average custom. It is not strange, but it is not the choice custom. Elsewhere they do not say so, [even though] it is applicable. It is as if camels are common everywhere, but they do not guard thorns for them. Even R. Eliezer would agree. Since they could do like Araviya, but they do not, the rest of the world is not drawn after them.

Ritva (DH Nimtzeis): For a strange custom, Batlah Daitam even for them, e.g. fodder and Hutzal. If it is not strange, but the rest of the world does not follow it, even though they could, it applies only where it is the custom. A proper custom appropriate for every place, but they do not follow it elsewhere because they need not or it is not common, that place is like the majority of the world, e.g. thorns according to R. Eliezer, and pomegranates according to Rabanan. This is only if it is the custom of a region. A person or family is never considered like the entire world, like we learn from pomegranates. However, perhaps the custom helps for them.

Poskim

Shulchan Aruch (YD 113:1): Something that is not eaten raw, and it is brought on kings' tables to accompany the bread, or a dessert, if a Nochri cooked it, it is forbidden due to Bishul Akum.

Pri Chodosh (3): Regarding what is eaten raw, does it depend on the person, or everyone? Hagahos Ashri connotes that it depends on the person. Surely this is wrong. Always, an individual's opinion is Batel Etzel Kol Adam. If one ate an amount that others fix a meal on, even if he did not fix, he must bless [Birkas ha'Mazon - Berachos 42a]. If one ate attached Terumah, Batlah Daito Etzel Kol Adam (Menachos 70a), and it is not considered eating. Here also, it depends on how everyone eats. We ignore the minority. If we would know that in most places where they have herring, they eat it raw, we would ignore places where they cook it. Hagahos Ashri did not know what most of the world does. Therefore, each place follows its custom.

Shiyurei Berachah (1): Mahari Binyamin asked Maharikash, if one does not eat raw cheese, and a Nochri cooked it, do we say that since most people eat it raw, Batlah Daito Etzel Kol Adam and it is permitted? We say so in Sukah (4a) about pillows and blankets (they are not Batel in a Sukah to diminish its height, for Batlah Daito) and about fixing a meal on wine (Berachos 35b). Or, perhaps there is different, for it depends on his desire. Here, he cannot tolerate raw cheese, so his opinion is not Batel, and it is forbidden to him. Maharik (58) learned from Rav (Avodah Zarah 38a), who said "anything eaten raw." If it depended on each person, he should have said "anything that he eats raw." This shows that we follow what people normally do. We are not concerned for the individual's opinion. Also, we forbid only what Chachamim explicitly decreed about Bishul Akum. They did not decree for every individual. Also the Gemara asked "what is the difference between the two versions", and did not say that the first version depends on each person, and the latter is the same for all. Also, we should equate them. The latter (what goes on kings' tables) does not depend on the individual.

Rebuttal (Shiyurei Berachah): Perhaps the Gemara did not need to say "anything that he eats raw." Since the decree was due to intermarriage, surely it depends on each person's opinion, lest he be drawn after Nochrim! Rav was not meticulous about his words, for people would not err about this. Maharikash said that we forbid only what Chachamim explicitly decreed. The Rosh (Chulin 1:23) says that the question about limbs of Nechirah teaches about a Tzibur that forbade a species to themselves starting at a set time, [and someone had left over from before]. We do not say that [surely], a decree on the Tzibur is not different for each individual! However, perhaps it is a uniform decree not to eat what is made after the set time. Maharikash said that the Gemara did not say that the versions differ about whether it depends on each person. Some Rishonim say that the Gemara does not list all the differences. Also, we list differences in which one version always permits, and the other always forbids.

Shiyurei Berachah: How did Maharikash and Mahari Binyamin overlook Hagahos Ashri, who forbids herring only to one who eats it raw? Why did they and the Pri Chodosh overlook the Rambam (Hilchos Ma'achalos Asuros 16:9), who rules like Rabanan and R. Akiva, that only seven things are considered important [and are never Batel]. He added that whatever is important to people in a place, e.g. nuts of Parech and pomegranates of Badan, is not Batel there. The Ritva in Avodah Zarah (38a) says that it depends on what is proper to eat raw, even if people usually cook it. If so, it does not depend on the person. However, one can ask about something that a person is loathe to eat raw.

Shiyurei Berachah: Bnei Chayei says that since Bishul Akum is due to being drawn after Nochrim, we do not say Batlah Daito. He says that Hagahos Ashri does not say that it depends on different lands, like the Pri Chodosh said, for he says "one who eats it raw..." I disagree with his first reason, for Chachamim made uniform decrees. The Ritva was lenient about anything proper to eat raw, even for those who cook it. I am not Medayek from "one who eats it raw...", for above Hagahos Ashri said "we, in our place..." This connotes that it depends on the place, like the Pri Chodosh. However, the Ritva in Eruvin says that any proper custom is not Batel in places where it is done. If so, we can say that Hagahos Ashri knew the world custom! However, Ra'avan says that it depends on what the majority of the world does, just like the Pri Chodosh.