On erev tisha b’Av we stop eating at shkiya (about 8:00 where I live in NY), but according to most Rishonim the prohibitions of aveilus such as not wearing leather shoes are not observed until nightfall. The Ramban, however, writes that the prohibition of bathing as beginning at shkiya and questions why the R”IF neglects to mention this halacha.
To explain this difference of opinion, the Brisker Rav suggested that mourning which we mark as we enter 9 Av and eat our final seudah hamafseket is patterned after the practices of aninus, the intense period of mourning between death and burial. Chazal poignantly describe how Tanaim would sit next to the furnace in their home, a lowly, isolated place, and eat in isolation, allowing themselves to become fully steeped in the somber mood of the day.
During the period of aninus the mourner is exempt from all mitzvos and is assumed to be completely involved in making the necessary preparations for the burial of the deceased. According to the Rambam the onein is exempt even from the obligations of mourning; the Ramban disagrees and holds that the negative prohibitions of mourning do apply.
The Brisker Rav suggests the dispute regarding bathing after seudah hamafesket as l’shitasam of this dispute regarding aninus. The Ramban who holds that even an onein is obligated in the prohibitions of mourning l’shitaso prohibits bathing from the moment seudah hamafseket concludes and the pseudo-aninus period of 9 Av begins. Rambam (and RI”F, according to the Brisker Rav’s understanding) who exempts an onein even from obligations of mourning does not prohibit bathing until nightfall. [Note: a similar analysis appears in the Keren Orah. The Brisker Rav's chiddush is actually a little different than what I presented here, so please see it in the original.]
The problem with this approach is that it does not seem to fit the words of the Ramban. Ramban tells us why he prohibits bathing – he writes that if one were to shower immediately before the fast, one would inevitably enjoy that refreshing afterglow of feeling clean and refreshed on the fast itself. Therefore, bathing and bathing alone is prohibited from even before the fast starts.
Given the reasoning presented by the Ramban, we perhaps have a new insight into why the seudah hamafseket is limited to a sparse meal. Were a heavy meal to be ingested immediately before the fast, it would lead to the experience of satiation and enjoyment extending into the fast itself, interfering with our experience of aveilut.
R’ Shternbruch in Moadim u'Zmanin (vol 5) goes a step further and suggests that in light of this Ramban we perhaps have an insight into why even on Shabbos we might temper our eating at the conclusion of the day and eat a small seudah hamafseket. The seudah hamafseket is not in and of itself connected with aveilus, but is simply a way to avoid indulging in a way that would lead us to experience the pleasure of satiation after Shabbos is over.
Again, reading the Tur’s presentation of the Avi Ezri’s justification of eating seudah hamafseket on Shabbos (which R’ Shternbruch makes no reference to) does not seem to me to support this approach. The TUr's language seems to indicate that the Avi Ezri’s aim was in fact to mark aveilus in some way - “m’shum churban” - Shabbos notwithstanding. This seems to be part of a broader pattern of practicing aveilus of 9 Av despite it being Shabbos. Two other practices which come to mind: The Rama quotes the minhag to not wear Shabbos clothes on Shabbos Chazon (a practice the GR”A opposed), and the minhag of many communities is to sing “Lecha Dodi” with the kinos tune of “Ali Tzion”.
My hunch is that these opinions view obligations of aveilus as stemming from the character of the day, the kedushas hayom, so to speak, much like the character of Yom Tov creates certain obligations of simcha. Demonstrating aveilus on Shabbos is not just an issur gavra imposed on the individual, but stems from the recognition that the kedushas hayom of Shabbos inherently in antithetical to mourning and sadness. Shabbos is a day of bracha (see Tosfos M.K. 23a quoting Yerushalmi). However, Shabbos Chazon is an exception. The special name we give to this Shabbos is not just to remind us of the haftarah, but perhaps indicates that the kedushas hayom of this Shabbos is different, and is impacted by the mourning period that it falls within. Derech derush perhaps one could say that Shabbos itself is in morning with us.
If our mourning can impact the kedushas hayom of Shabbos, perhaps one might argue as well that the scale can be tipped in the opposite direction and the kedushas hayom of Shabbos can impact our mourning. Perhaps this Shabbos Chazon will be the Shabbos that we will once again experience v'techezeina eineinu b'shuvcha l'Tzion b'rachamim.
Kol hamisabeil al Yerushalayim zoche v'ro'eh b'simchasa...