Fast of the Firstborns

R. Shmaryahu Shulman, in his Merish Ba-Birah on Parashas Bo (p. 61a), raises an issue that is relevant to this year's calendar. Every year, firstborn sons are, due to ancient custom, expected to fast on the day before Pesah, although the practice has become to celebrate the completion of a talmudic tractate (siyum) thereby overriding the fast. When the fast falls out on Friday, the custom is to fast on that day even though we normally do not fast on Fridays. The reason for this is that we generally do not fast on Fridays because it is improper to recite so much selihos on the day before Shabbos and/or one should not enter Shabbos extremely hungry. However, since the firstborns do not recite selihos on that day and there is a long tradition (perhaps even requiremtn) to enter Pesah hungry the reasons for pushing off the fast do not apply and it remains on Friday. However, when the fast falls out on Shabbos it must be moved. It cannot be moved later, because then it would have to be pushed off until after Pesah, over a week later. The Shulhan Arukh (Orah Hayim 470:2) records two opinions of what to do when the fast falls out on Shabbos. One is to simply nullify the fast for that year. The other is to observe it on Thursday, and this is the customary practice.

R. Shulman points out that when Ta'anis Esther is pushed back to Thursday and then there is a festive meal that overrides the fast, those who eat are expected to fast the next day (Rama in Shulhan Arukh, Orah Hayim 686:2), and such is normative practice. If that is the case, then it would seem that firstborns who eat at a siyum on the Thursday fast day should then fast on the next day as well, or at least make another siyum on Friday. He points out that R. Moshe Shternbuch (Teshuvos Ve-Hanhagos 2:211) raises this issue as well. R. Tzvi Pesach Frank (Mikra'ei Kodesh, Pesah vol. 2 no. 23) recommends eating some left-overs from the siyum on Friday.

However, R. Moshe Feinstein (Iggeros Moshe, Orah Hayim 4:69) and R. Moshe Shternbuch rule that the normative practice is not to be strict because this fast is merely customary. The Piskei Teshuvos (470:4) writes that the medakdekin make another siyum on Friday.

R. Tzvi Pesach Frank quotes the Yeshu'os Ya'akov (470) as raising another problem. Normally, a siyum would not override a fast because the meal for the siyum can be eaten later that night after the fast is over. However, since on a normal erev Pesah that is impossible because the seder will be held that night, the siyum meal must be eaten during the day and therefore override sthe fast. When the fast falls out on Thursday and the seder will be on Saturday night, we return to the original point and the siyum meal should not override the fast. R. Frank quotes R. Avraham Kook as explaining that the replacement-day cannot be more stringent than the original-day. Since the Thursday fast is a replacement for the Friday fast, the Thursday fast cannot be stricter and, therefore, a siyum meal must have no less an impact on Thursday than it does on Friday.