Does the concept "Shevua Shechal Bo" come up within the context of halacha or hashkafa in any area other than the the week leading up to Tisha B'Av? It just seems like a unique measure for a period of time, unlike say a 7 day period for mourning which matches a full week. I'm wondering if there are any justifications for why it applies to Tisha B'Av and seemingly nowhere else.

  • Shavua Shechal Bo is too a 7 day period of mourning that happens to always start on Sunday. It's much smoother to start on Sunday because you don't have to have a nonmourning day of Shabbat in the middle
    – Double AA
    Jul 11, 2021 at 3:42
  • @DoubleAA But could it ever work out to be a full 7 days? (whether in our current fixed calendar cycle or the ones determined beforehand via witnesses). Tisha B'Av would then get pushed to the next Sunday. So it would be a period of 7 days (if Shabbat is included) of intense mourning before a day which has even more intense mourning.
    – Ari
    Jul 11, 2021 at 3:55
  • Shavua Shechal Bo is always the whole week. See Taanit 30a. There are two opinions for when to observe the mourning: from Rosh Chodesh until tisha bav, or the whole week of tisha bav. We rule leniently both ways and just observe the week of tisha bav until the fast, so we don't really observe the whole Shavua Shechal Bo
    – Double AA
    Jul 11, 2021 at 3:57
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    Ashkenazi minhag of selichos is another example of shavua shechal bo (unless there's less than 4 days in which case it starts the week before)
    – Chatzkel
    Jul 11, 2021 at 4:15
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    Perhaps the difference between regular aveilus and tisha bav is that by aveilus the first day is peak of mourning, (onen, etc.) Then there's the first 3 days which are in between, then the last 4 days are the least. Whereas by tisha bav it's the opposite, with the days leading up being less mourning, and the last day, Tisha bav, being the peak. So if the point is to lead up to a peak instead of away from a peak then we try not to have a break in the middle for shabbos. This would maybe explain selichos as well, since they lead up to Rosh hashanah
    – Chatzkel
    Jul 11, 2021 at 4:19


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