1) HALACHAH: A PERSON FROM ERETZ YISRAEL IN CHUTZ LA'ARETZ FOR YOM TOV
OPINIONS: The Gemara establishes that one who normally observes only one day of Yom Tov (such as a resident of Eretz Yisrael) must refrain from Melachah for two days of Yom Tov when he finds himself outside of Eretz Yisrael in a Jewish community that observes two days of Yom Tov.
Why must he conduct himself like the residents of the place where he spends Yom Tov? Must he conduct himself exactly like the local residents, or only to a certain degree?
(a) The RAMBAM (Hilchos Yom Tov 8:20) does not distinguish between the requirement to refrain from Melachah on the second day of Yom Tov outside of Eretz Yisrael and any other Minhag. He writes with regard to all Minhagim that if a person intends to return to his original place, he may conduct himself according to the Minhag of his original place. However, in order to avoid discord, he should not do Melachah where others might see him, as the Mishnah teaches (50a-b). The Rambam's words imply that a person from Eretz Yisrael who spends Yom Tov in Chutz la'Aretz (and intends to return to Eretz Yisrael) is permitted to do Melachah on Yom Tov Sheni in private. This indeed is the conclusion of a number of authorities (TAZ OC 496:2, citing MAHARSHAL; RAV OVADYAH YOSEF in YECHAVEH DA'AS 3:35).
(b) TOSFOS (52a, DH b'Yishuv, see also RAN) writes that the Minhag to refrain from Melachah on Yom Tov Sheni is more stringent than other Minhagim, because it is not possible to do Melachah in private without it becoming known that Melachah was done. (Even though there are some Melachos that can be done quietly without becoming known, the Rabanan did not differentiate and they prohibited all Melachos in private. See MACHATZIS HA'SHEKEL OC 496:4.) Therefore, wherever Melachah is prohibited, it is prohibited even in private.
However, it is still not clear exactly what type of Melachah is prohibited in private. TOSFOS (51a, DH Iy Ata) points out an apparent contradiction. The Mishnah states unequivocally that one must conduct himself according to the strict practice (Chumra) of the place he visits, because he must avoid discord. However, the Gemara says that the reason he must conduct himself according to the Chumra of the place is because of the Kusim in that place, who will misunderstand his conduct and will permit other things that really are forbidden. The Gemara seems to give a different reason than the Mishnah.
Tosfos cites the RI who explains that the Mishnah refers to a "Minhag Chashuv," a Minhag with a strong basis. One may not be lenient with regard to such a Minhag even in front of Talmidei Chachamim who understand his reason for being lenient. On the other hand, one may be lenient with regard to a Minhag which does not have a strong basis, and which became an accepted practice only as a result of a mistake or which evolved without the consent of the Chachamim. However, one may not act leniently with regard to even this type of Minhag in front of Kusim.
Tosfos cites the RASHBA (Rabeinu Shimshon mi'Shantz), who says that the Mishnah refers to a person who does not have intention to return to his original place ("Ein Da'ato Lachzor"), in which case he takes on the Minhag of the place at which he has arrived, whether its populace is learned or ignorant, because he is considered as though he has already become a member of that community. In contrast, when he has intention to return to his original place, he does not take on the Minhag of the new place unless there are Kusim there. (This also appears to be the ruling of the RAMBAN in Milchamos.)
The Minhag of Yom Tov Sheni fits the criterion of a Minhag with a strong basis (see Beitzah 4b). Therefore, according to the RI, one who comes from Eretz Yisrael to Chutz la'Aretz should adopt that Minhag in order to prevent discord, even if he intends to return to Eretz Yisrael.
The RASHBA, however, is more lenient. According to the Rashba, only one who does not intend to return to Eretz Yisrael is required to observe the second day of Yom Tov in Chutz la'Aretz. If he intends to return to Eretz Yisrael, he may perform Melachah on the second day of Yom Tov as long as there are no Kusim in that place, but only Talmidei Chachamim.
As mentioned above, Tosfos maintains that whenever one is forbidden from performing Melachah on the second day of Yom Tov, he may not perform Melachah even in private. Consequently, according to the RI, one may not perform Melachah at all, even in private and even when there are no Kusim present. According to the RASHBA, he may not perform Melachah in private only in a place where there are Kusim.
(c) The BA'AL HA'ME'OR explains that when the Mishnah states that one must be stringent and follow the Minhag of the place in order to prevent discord, it means that he must be stringent only in a place where there are Kusim. Accordingly, one should be permitted to do Melachah on Yom Tov Sheni in a place in which only Talmidei Chachamim reside.
However, the Ba'al ha'Me'or explains that the Minhag to refrain from Melachah on Yom Tov Sheni is a stronger Minhag than any other, and therefore one must be stringent and refrain from Melachah even in a place where there are only Talmidei Chachamim. (The Acharonim understand that the Ba'al ha'Me'or means that even in private one may not do Melachah.) Consequently, not only is Melachah prohibited in private on Yom Tov Sheni, but Yom Tov Sheni must be observed in all of its aspects when a person is in Chutz l'Aretz, even in private.
(d) The RA'AVAD on the Rif writes that when a resident of Eretz Yisrael travels to Chutz la'Aretz, there is no question which Minhag he should choose, whether to do Melachah on Yom Tov Sheni or not to do Melachah on Yom Tov Sheni. There is no Minhag whatsoever for a resident of Eretz Yisrael to do Melachah in Chutz la'Aretz on Yom Tov Sheni. A resident of Eretz Yisrael must observe Yom Tov Sheni when he is in Chutz la'Aretz.
The Ra'avad apparently understands the Gemara here like TOSFOS in Sukah (43a; see Insights to Pesachim 51:3), who explains that even people from Eretz Yisrael have a Minhag to observe two days of Yom Tov when they are in a place which the messengers of Beis Din cannot reach. Their Minhag is that when they go to Chutz la'Aretz, they observe two days of Yom Tov.
HALACHAH: The SHULCHAN ARUCH (OC 468:4) rules like TOSFOS and the RI, that one must be stringent even in the presence of Talmidei Chachamim, and in private (MISHNAH BERURAH 468:14). One who is in a "Midbar," or outside the boundary (Techum) of the nearest Jewish community, is permitted to do Melachah on Yom Tov Sheni, as long as he intends to return to Eretz Yisrael. If he does not intend to return, then he must observe the Minhagim of Chutz la'Aretz immediately, even while he is in a Midbar and has not yet reached the Jewish community in Chutz la'Aretz. (See also SHULCHAN ARUCH OC 496:3.)
2) FOLLOWING THE CUSTOMS OF THE PLACE ONE VISITS
QUESTION: The Gemara first understands that Rebbi Yehudah in the Mishnah (50b) maintains that one is not required to perform Bi'ur with fruit of Shemitah that was brought to a place where that type of fruit is no longer found in the fields, when that type of fruit has not yet disappeared from the fields in the place where it originated. The Gemara challenges this interpretation of Rebbi Yehudah from the beginning of the Mishnah, which states that one is required to observe the stringencies of the place he visits.
RASHI (DH v'Leis Lei) addresses an obvious problem with the Gemara. The Mishnah says that one must observe the stringencies of the place he visits in order to avoid dispute ("Mipnei ha'Machlokes"). In this case, however, there is no potential for dispute; the person's conduct depends simply on whether or not the fruit in his place of origin is still in the fields. "Mipnei ha'Machlokes" applies only when one person or group does not accept the stringent practice of another group. It does not apply to the case of Shemitah fruit, because the fruit that comes from out of town has different properties than the local fruit.
Rashi explains that the Gemara infers from the Mishnah that there is another reason that requires one to observe the stringencies of the place he visits, besides the concern for Machlokes: When a person visits a certain place, he is bound by the Minhagim of that place simply by virtue of his presence there.
Rashi proves this from the fact that one must observe the stringent practices of his place of origin. Obviously, one will not incite Machlokes if he disregards the stringent practices of the place from which he came when he is not there! Why must he observe the practices of his place of origin when he is not there? It must be because those practices are considered to be his own Minhagim. Similarly, one must observe the stringent practices of the place he visits simply because those practices are binding on anyone in that place.
Rashi's words are not clear. The Mishnah explicitly states that the reason one observes the Minhagim of the place he visits is in order to avoid discord (see also the statement of Abaye on 51b). Why does Rashi assert that there is a second reason?
ANSWERS:
(a) The SEFAS EMES writes that when the Mishnah says "Mipnei ha'Machlokes," it refers to one who performs Melachah in public when he intends to return to his place of origin ("Da'ato Lachzor"). In contrast, the reason that Rashi adds applies to one who has no intention to return ("Ein Da'ato Lachzor").
(b) Perhaps Rashi understands that when the Mishnah says "Mipnei ha'Machlokes," it is giving an additional reason for why one must conduct himself according to the Minhag of the place. The Mishnah means that one must observe the Minhag of the place he visits for two reasons. First, that place becomes his place of residence, and thus he becomes bound by all of its Minhagim. Second, he must conduct himself in a way that will avoid Machlokes.

52b----------------------------------------52b

3) WHAT IS "BI'UR"?
OPINIONS: The Gemara quotes the Mishnah in Shevi'is (9:2) which teaches that Eretz Yisrael is divided into three regions with regard to the requirement to perform Bi'ur with fruit of Shevi'is. Those three regions are Yehudah, Ever ha'Yarden, and the Galil. When a particular type of fruit is no longer found in the fields in one region, the requirement of Bi'ur takes effect for that region. The laws of Bi'ur require that in the Shemitah year, after the time that a fruit is no longer available in the field, one must be Meva'er (destroy) that fruit.
What constitutes Bi'ur?
(a) The RAMBAM (Hilchos Shemitah 7:1-3) explains that Bi'ur means that the produce becomes prohibited to be eaten and it must be burned or destroyed (or eaten before the time of Bi'ur arrives). (The Rambam understands the meaning of "Bi'ur" in this context to be similar to the meaning of "Bi'ur Chametz," the destruction of Chametz.)
This also seems to be the view of RASHI here (DH Mishum), who says that the fruit is destroyed by being left out in an open area where it will be trampled by animals. Similarly, Rashi in Nidah (51b, DH Kol she'Yesh Lo) says that Bi'ur means to remove the fruit from one's home. (See also Rashi to Bava Kama 101b and Yevamos 122a.)
(b) TOSFOS (DH Misba'arin), the RAMBAN (Vayikra 25:7), and the RASH (Shevi'is 9:8) explain that there is no requirement to burn or destroy produce of Shemitah at the time of Bi'ur. Rather, one must simply declare the produce ownerless (Hefker) so that anyone may take it. Once the produce has been made Hefker, even the owner himself may reclaim it and eat it for as long as he wants.
The Ramban proves this from the Tosefta (Shevi'is 8:4) that states that at the time of Bi'ur, a person must take the Shevi'is fruit into the street and make it Hefker so that anyone may take it, and afterwards he may bring it back into his home and eat it until it is finished. This implies that Bi'ur involves simply taking the fruit out of one's home and making it Hefker (similar to "Bi'ur Ma'aseros" that is performed in the fourth and seventh years of the Shemitah cycle). The Ramban cites further support for this explanation from the fact that the Mishnah in Temurah (7:4-6) does not mention produce of Shemitah in the list of Isurei Hana'ah (objects from which one may not derive benefit) that must be either buried or burned.
(c) The RA'AVAD (Hilchos Shemitah 7:3) writes that Bi'ur involves elements of both of the abovementioned opinions. There are two different types of Bi'ur that must be done with fruit of Shevi'is. When fruit of Shevi'is is no longer available in a particular city or location, a person who lives in that location must declare any fruit of Shevi'is in his possession to be ownerless, or bring the fruit to Beis Din to distribute. However, when a particular fruit is no longer available in any entire region (Yehudah, Ever ha'Yarden, or Galil), the fruit in one's possession must be destroyed.
HALACHAH: The CHAZON ISH rules that today we may be lenient and conduct ourselves according to the RAMBAN, because the laws of Shevi'is today are only mid'Rabanan. (See also Insights to Bava Kama 101:2 and Nidah 51:3.)

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