“Question: Isn’t ta’anis bechorim supposed to be a fast day? Why does everyone just listen to a siyum and then eat as usual?
Discussion: The Shulchan Aruch (Orach Chayim Siman 470 se’if 1) rules that firstborns are supposed to fast on Erev Pesach (and this includes both firstborns from the father or from the mother).
The Mishna Berura (Siman 470 s.k. 2) writes that the bechorim recite “aneinu” in shome’a tefilla during Mincha; and if there are ten bechorim who are davening together, then the sheliach tzibbur should likewise recite “aneinu” in shome’a tefilla (as on a ta’anis yochid). However, the Mishna Berura concludes that it is preferable that a bechor should not be the sheliach tzibbur in such a situation, so as not to publically mention the ta’anis because it is chodesh Nissan.
There is no mention in the Shulchan Aruch that if one attends a siyum (or any other se’udas mitzvah) then this will exempt him from the ta’anis. The Magen Avraham (ibid, at the beginning of the siman) quotes an opinion (the Olas Shabbos in the name of the Maharash Halevi) that allows bechorim to eat at a se’udas bris milah, but the Magen Avraham himself disagrees with this opinion. The Mishna Berura (s.k. 10) writes that whether or not bechorim may eat at a se’udas mitzvah (such as a se’udas bris milah or pidyon haben) depends on the minhag of each area.
Although we find virtually no mention of attending a siyum maseches in the earlier Poskim, the Mishna Berura concludes that the minhag in many areas is to be lenient and to eat even at the se’udah of a siyum (masechto) and even if the bechorim in attendance have not themselves finished the masechto; since regarding the individual making the siyum it is considered a se’udas mitzvah, all [bechorim] who are attending may participate in the se’udah. The Mishna Berura (ibid) also writes that the minhag is that the mesayem finishes the masechto in front of the bechorim, and they listen to, and participate in the siyum and then partake of the se’udah.
The predominant minhag among klal yisroel today is to be lenient (in line with the view of the Mishna Berura) and participate in a siyum and to consider this as attending a se’udas mitzvah and therefore not to fast. The reason for this lenient conduct appears to be because the institution of ta’anis bechorim is a minhag (see Mishna Berura ibid s.k. 7) and generally people are weaker nowadays (c.f. Igros Moshe Orach Chayim volume 4 Siman 69:4) than they were in previous generations and were bechorim to fast on Erev Pesach this is likely to impair their ability to fulfil all mitzvos of leil haseder (i.e. drinking four cups of wine and eating matza) properly. Therefore virtually all bechorim make or attend a siyum and consider this as having attended a se’udas mitzvah which, according to some authorities exempts the attendees from fasting.
Conclusion: Although ta’anis bechorim was instituted as a fast day for all bechorim, and this has been codified in the Shulchan Aruch; the widespread minhag is to be lenient and not only to eat if there is a se’udas mitzvah, but also to l’chatchilo find a se’udas mitzvah to attend, or even to make or attend a siyum. (A bechor who wishes to be stringent and to fast should keep in mind that he will be going from the fast straight into leil haseder and will have to eat matzah and moror and drink four cups of wine. It would be indeed be unfortunate if fasting on Erev Pesach comes at the expense of not performing one of the mitzvos leil haseder correctly).
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