The Gemara, Beitzah 4b, cites Abaye who states that the practice of observing an additional day of Yom Tov in the Diaspora (Yom Tov Sheini Shel Galuyot) originated in the times when Beit Din would establish the new month based on an eyewitness account of the new moon. It often took an extended period of time to communicate this message to the communities in the Diaspora. For this reason those communities observed an additional day of Yom Tov. Abaye notes that although nowadays, the new month is not established based on an eyewitness account, and the calendar is fixed and known to all, those in the Diaspora continue to observe an additional day of Yom Tov. This article will discuss two approaches to understand Yom Tov Sheini Shel Galuyot and the practical differences between the two approaches.

Yom Tov Sheini Shel Galuyot: Rabbinic Decree or Minhag?
The Gemara, ibid, quotes a dispute between Rav and Rav Asi as to whether the first day of Yom Tov and Yom Tov Sheini Shel Galuyot are considered one elongated day or two distinct days. Rashi ad loc., explains that Rav, who holds that the two days of Yom Tov are two distinct days, is of the opinion that since both days cannot logically coexist, they are treated as two independent days. Rav Asi, who is of the opinion that both days are considered one elongated day, is of the opinion that the observance of Yom Tov Sheini Shel Galuyot nowadays is based on a rabbinic decree that defines the day as an extension of the first day of Yom Tov. The Gemara implies that one practical difference between Rav and Rav Asi is whether there is an obligation to recite Havdalah between the first day of Yom Tov and Yom Tov Sheini Shel Galuyot. If the two days are two independent days, there should be an obligation to recite Havdalah. If they are considered one elongated day, there is no obligation to recite Havdalah.

Rashba, Beitzah 4b, s.v. V'Hashta, notes that although we follow the opinion of Rav, we don't recite Havdalah between the two days of Yom Tov. He explains that when the Gemara suggests Havdalah as a practical difference between the opinions of Rav and Rav Asi, it is following the opinion of R. Eliezer (Eiruvin 39a) that there is no concern of desecrating Yom Tov Sheini Shel Galuyot by treating Yom Tov Sheini Shel Galuyot as a day of doubt vis-א-vis the first day of Yom Tov. However, the normative opinion is that of the Chachamim who disagree with R. Eliezer and maintain that certain activities constitute a desecration of Yom Tov Sheini Shel Galuyot. Rashba maintains that reciting Havdalah on Yom Tov Sheini Shel Galuyot for the first day of Yom Tov would constitute a desecration of Yom Tov Sheini Shel Galuyot.

It is clear from Rav Asi's opinion that Yom Tov Sheini Shel Galuyot is considered a full-fledged rabbinic decree. There are two possible reasons why Rav disagrees. Perhaps he disagrees because he does not consider Yom Tov Sheini Shel Galuyot to be a rabbinic decree but rather an ancient minhag (tradition). Or perhaps he agrees fundamentally that it is considered a rabbinic decree. Rather, he disagrees on the grounds that the rabbinic decree was not formulated in manner that Yom Tov Sheini Shel Galuyot is considered an extension of the first day of Yom Tov.

This question seems to be the basis of a dispute between Rabbeinu Tam (cited in Tosafot, Sukkah 44b, s.v. Kan) and Ran, Sukkah 22a, s.v. Itmar. Rabbeinu Tam is of the opinion that Yom Tov Sheini Shel Galuyot is not based on a rabbinic decree but on a minhag. Ran disagrees and maintains that it is based on a rabbinic decree.

Ran questions Rabbeinu Tam's approach from the beracha recited on the matzah on Yom Tov Sheini Shel Galuyot. The beracha recited on the matzah on the second night of Yom Tov includes the term "v'tzivanu" (you commanded us). The Gemara, Shabbat 23a, states that it is appropriate to recite "v'tzivanu" on a rabbinic decree. Ran claims that it is not appropriate to recite "v'tzivanu" on a minhag.

In defense of Rabbeinu Tam, it should be noted the Gemara, ibid, states that the berachot recited on Yom Tov Sheini Shel Galuyot are not necessarily warranted and the reason why they are recited is so that it does not lead to a desecration of Yom Tov. R. Ya'akov Y. Kanievski, Kehillat Ya'akov, Berachot no. 8, explains that the recitation of the beracha on matzah on Yom Tov Sheini Shel Galuyot is not reflective of any commandment of the mitzvah. Rather, the reason why one recites a beracha on Yom Tov Sheini Shel Galuyot is because the purpose of Yom Tov Sheini Shel Galuyot is to replicate the experience of the Jews in the Diaspora in times when they were actually in doubt as to which day was the authentic Yom Tov. In those times, they recited a beracha on the matzah on both of the days that they observed as Yom Tov. In trying to replicate that experience, we recite berachot. The berachot we recite are not berachot on the actual mitzvot that we fulfill, but rather have intrinsic significance in trying to replicate the experience of ancient times.

Practical Differences Between the Two Approaches
There are a few potential practical differences between the approach that Yom Tov Sheini Shel Galuyot is based on a rabbinic decree and the approach that Yom Tov Sheini Shel Galuyot is based on a minhag. First, there is a rule that a circumcision that is not performed on the eighth day may not be performed on Shabbat or Yom Tov. Rambam, Hilchot Milah 1:15, rules that a circumcision that cannot be performed on Shabbat or Yom Tov may be performed on Yom Tov Sheini Shel Galuyot. Rabbeinu Asher, Teshuvot HaRosh 26:6, prohibits a delayed circumcision on Yom Tov Sheini Shel Galuyot. [Shulchan Aruch, Yoreh Deah 266:8, rules in accordance with the opinion of Rabbeinu Asher. Shach, Yoreh Deah 266:8, rules in accordance with the opinion of Rambam.]

Perhaps the dispute between Rambam and Rabbeinu Asher is contingent on the nature of Yom Tov Sheini Shel Galuyot. If Yom Tov Sheini Shel Galuyot is based on a minhag, it is arguable that the biblical commandment to perform a timely circumcision (see Teshuvot Noda B'Yehudah, Yoreh Deah 2:166) overrides the minhag to refrain from melacha on Yom Tov Sheini Shel Galuyot. However, if Yom Tov Sheini Shel Galuyot is based on a rabbinic decree, it is within rabbinic authority to suspend a biblical mitzvah when it interferes with the observance of a rabbinic decree (see Yevamot 90b).

Second, there is a lengthy discussion among the Poskim regarding a resident of the Diaspora who visits Israel on Yom Tov and plans to return after Yom Tov. Mishna Berurah, 496:18, notes that majority of the Acharonim rule that in such a situation, the resident of the Diaspora should observe two days of Yom Tov. Mishna Berurah references the opinion of R. Shneur Zalman of Liadi, Shulchan Aruch HaRav, Orach Chaim 496:11, who maintains that he should only observe one day of Yom Tov.

Perhaps the issue of whether a resident of the Diaspora who visits Israel should observe Yom Tov Sheini Shel Galuyot is contingent on the nature of Yom Tov Sheini Shel Galuyot. If Yom Tov Sheini Shel Galuyot is a rabbinic decree, it is likely that the decree is location-based so that those who are in Israel don't observe Yom Tov Sheini Shel Galuyot and those in the Diaspora observe Yom Tov Sheini Shel Galuyot. However, if Yom Tov Sheini Shel Galuyot is based on a minhag, the observance of Yom Tov Sheini Shel Galuyot is not based on location but on the individual. Like all minhagim, a person follows the practices of the place in which he resides even he visits another location (Mishna Pesachim 50a). Since all communities of the Diaspora have accepted the minhag of observing Yom Tov Sheini Shel Galuyot, all residents of those communities must also observe Yom Tov Sheini Shel Galuyot.

[R. Chaim Soloveitchik (cited in Mesorah Vol. VI pg. 18) is of the opinion that in principle one should only observe one day of Yom Tov. However, one should also follow the stringencies of the minhag of the place in which he resides. Therefore, his prayers should be that of weekday (or Chol HaMoed) and he should don tefillin. However, he should refrain from melacha in order to follow the minhag of the place in which he resides. This opinion is popularly known as "a day and a half."]