Among the four fast days commemorating Jerusalem's destruction, the tenth of Tevet occupies a peculiar position. It marks neither the breach of the city walls, like the seventeenth of Tammuz, nor the Temple's burning, like Tisha B'Av, nor even the final extinguishing of Jewish sovereignty, like the Fast of Gedaliah. Instead, it commemorates something subtler: the beginning. On this day, the Babylonian king laid siege to Jerusalem—not destruction itself, but its commencement, the moment when the trajectory toward catastrophe began.

This distinction opens into a fascinating legal puzzle that has occupied rabbinic authorities for centuries, centering on a remarkable claim made by the Abudraham and rippling outward into fundamental questions about the nature of fasting, mourning, repentance, and the significance of specific dates in Jewish memory.

The Abudraham's Claim

The Beit Yosef, in his commentary on the Tur (Orach Chaim 550), quotes an extraordinary statement from the Abudraham: this fast differs from the others because if it were to fall on Shabbat, we could not postpone it to another day. The verse states "on this very day" (Yechezkel 24:2)—the same language used for Yom Kippur, which overrides Shabbat.

The Beit Yosef immediately questions this: "From where does he derive this?" We have no Talmudic tradition that the tenth of Tevet would override Shabbat. Indeed, in our calendar calculations, it never falls on Shabbat. The Minchat Elazar (I, 48) sharpens the question: Even though the Abudraham offers a scriptural source, who says we can derive new laws from prophetic verses through our own exposition when no such derivation appears in the Talmud itself? These fasts originate in scriptural verses from the prophets, yet we don't find this specific law anywhere in rabbinic literature.

Yet the very novelty of the Abudraham's position demands explanation. Why would this fast—seemingly the least significant of the four, commemorating merely the siege's beginning rather than actual destruction—possess a quality that would even theoretically override Shabbat?

Talmudic Evidence and Challenges

The Or Same'ach (Hilkhot Ta'aniyot 5:6) offers an possible Talmudic source, drawing on Eruvin (40b). The Talmud there asks whether one fasting on Friday afternoon must complete the fast all the way until the onset of Shabbat; but the question is posed only regarding individual fasts, not communal ones. The Or Same'ach explains why: because the four fasts cannot fall on Friday—except the tenth of Tevet, and in that case he question need not be asked. If the tenth of Tevet itself could theoretically be observed on Shabbat, certainly one continues fasting from Friday afternoon into Shabbat evening.

However, Rashi on Megillah (5a) presents a direct challenge. Explaining that when Tisha B'Av falls on Shabbat it is postponed to Sunday, Rashi adds that the same applies to the tenth of Tevet and the seventeenth of Tammuz—they too are postponed when they would fall on Shabbat. This seems to contradict the Abudraham directly.

The Hitorerut Teshuvah attempts a partial reconciliation: Perhaps the Abudraham also doesn't mean we would actually fast on Shabbat, but rather that the fast cannot be postponed to Sunday—it might not be observed at all that year, since "this very day" indicates the obligation attaches specifically to the tenth of Tevet itself. (See also Resp. Shoel U’Meishiv, Kama, III, 179.)

The Nature of the Prophetic Command

The Minchat Chinukh (Mitzvah 301) poses a fundamental question: Why, in fact, don't the four fasts override Shabbat? They originate in prophetic decree—recorded in scriptural verses, a status termed divrei kaballah—which carry greater weight than rabbinic enactments. The prohibition against fasting on Shabbat is of comparable basis, deriving from the commandment to make Shabbat delightful, which is found in the book of Isaiah. Shouldn't the prophetically endorsed fasts be at least equal in importance?

He answers that the prophetic verses don't actually specify fasting on particular dates. They mention only months: "the fast of the fourth month, the fast of the fifth month, the fast of the seventh month, and the fast of the tenth month" (Zekharyah 8:19). The precise dates within those months were established by rabbinic interpretation. Therefore, if a date falls on Shabbat, we fulfill the prophetic mention by fasting on a different day within that month.

This implies something significant: the four fasts aren't fundamentally about specific calendar dates. They commemorate events that occurred in particular months, but the obligation doesn't attach to the anniversary date itself in an absolute way. We're commanded to observe fasts during those months, not necessarily on the precise seventeenth, ninth, third, and tenth.

Several authorities use this framework to defend the Abudraham. The tenth of Tevet differs because the verse specifies "on this very day." This phrase elevates the date itself from ideal commemoration to essential component of the obligation. While other fasts can be observed on any appropriate day within their respective months, the tenth of Tevet must occur on that specific date.

The Significance of Beginning

But why would "this very day" carry such weight for the siege's commencement? Rav Chaim Soloveitchik (Chiddushei HaGrach, Siman 44) offers an important insight. He invokes the concept ta'anit chalom—a fast after a disturbing dream, which may be observed even on Shabbat. Why? Because the fast is "beneficial for the dream" specifically on that day—fasting immediately can nullify the dream's negative implications.

Most fasts commemorate past events. We fast on the seventeenth of Tammuz because the walls were breached; we fast on Tisha B'Av because the Temple burned. These events occurred on specific dates, but our fasting is essentially memorialization. If we fast on the sixteenth or eighteenth, we've still engaged in the memorial act—the precise date matters less than remembering and mourning.

The tenth of Tevet differs fundamentally. The verse emphasizes "on this very day" because the significance isn't merely the historical event but the day itself. The tenth of Tevet marks a beginning—the initiation of catastrophe, the moment when the trajectory toward destruction commenced. And a beginning, by its nature, cannot be transferred to another date. If we observe "the day the siege began" on the eleventh or twelfth, we're no longer marking the beginning. We're commemorating something that happened earlier but observing it later. But "this very day" language indicates the day itself carries inherent significance inseparable from the calendar date.

Rabbi Shimshon Pinkus, in his sefer Tiferet Torah (Siman 16), develops this insight. Most fasts memorialize specific catastrophic events—independently terrible occurrences. The seventeenth of Tammuz marks the walls' breach; even if nothing further had happened, breaching Jerusalem's walls would warrant mourning. The tenth of Tevet stands apart. If the siege had been lifted after several days, if the Babylonians had withdrawn, if no destruction had followed—would we fast on this date? Presumably not. The siege's commencement possesses significance only retrospectively, only because of what it initiated.

Rabbi Pinkus articulates this precisely: The tenth of Tevet isn't fundamentally about the event but about the day. The other fasts commemorate tragic events, and therefore the specific date matters less than remembering what occurred. But the tenth of Tevet commemorates when everything began—and you cannot observe 'beginning day' on a different date.

He draws a comparison to yahrzeit—the anniversary of a parent's death, when many have a practice to fast. The Shulchan Arukh rules that if a yahrzeit falls on Shabbat, one postpones the fast to Sunday. The Rama rules that one doesn't fast at all that year. Why not postpone? Because the yahrzeit isn't actually about mourning the death itself—if it were, we could mourn on any day. It's about the significance of the specific date, the day when loss struck that family. If we cannot mark that day itself, the observance loses meaning.

Mourning Versus Repentance

The Gevurat Yitzchak (Chanukah and Purim, Siman 50) identifies two fundamentally different types of fast days. Some function as days of mourning and grief—we abstain from pleasure because tragedy occurred. These fasts naturally extend day and night, include all forms of affliction, and conflict with Shabbat's essential character. Mourning is prohibited on Shabbat as a fundamental contradiction—grief opposes joy.

Other fasts serve as vehicles for repentance and prayer. We fast not from grief but to inspire spiritual transformation. These fasts need only restrict eating and drinking during daylight hours. And these don't inherently conflict with Shabbat's holiness. Yom Kippur demonstrates that fasting can coexist with sacred time when the purpose is spiritual elevation rather than mourning.

The Gevurat Yitzhak suggests the tenth of Tevet was never structured like the others. It was never primarily about mourning a completed tragedy. From its inception, this fast served as a day of repentance and divine judgment—marking when destruction's trajectory began, when the decree commenced.

This distinction carries profound implications. Mourning fasts cannot override Shabbat because they represent grief, contradicting Shabbat's joy. But repentance fasts don't inherently contradict Shabbat. When the prophetic text explicitly requires fasting "on this very day," and when that fast serves spiritual elevation rather than mourning, the case for overriding Shabbat's rabbinic restriction becomes plausible.

The First of the Fasts

You're right. Let me look more carefully at what the Uri VeYish'i says about divine intentionality:

The First of the Fasts: The Uri VeYish'i's Framework

The sefer Uri VeYish'i offers a crucial insight into why the tenth of Tevet cannot be moved. The key lies in understanding that the tenth of Tevet is not merely one of four fasts but the first of them—and as the first, it represents a moment of divine intentionality, where a specific time was designated by Heaven for a particular spiritual response.

The Uri VeYish'i explains that when God designates a specific moment in time as the opportunity for a particular spiritual response—for repentance, for averting judgment, for redirecting trajectory—that represents a deliberate divine choice. Heaven has determined that this precise moment shall serve as the appointed time for this spiritual work. The designation itself reflects divine intentionality: God has structured time such that this particular date carries unique spiritual potential and receptivity.

This is fundamentally different from commemorating a past event, where the essential act is remembering what occurred and the specific date has some flexibility. When a day is divinely appointed as the time for spiritual response—when God has intentionally structured that moment in time as the window for addressing judgment—moving it to another date doesn't simply shift the commemoration. It rejects the divine designation. It treats as arbitrary what Heaven has determined to be significant.

The intentionality matters because it means we cannot casually transfer what God has specifically appointed. When Heaven designates "this very day" as the moment for response, that reflects a deliberate divine choice about when the opportunity for repentance and transformation exists. The spiritual work that needs to be accomplished is tied to that precise moment not by accident or convenience, but by divine intent. Postponing the fast means disregarding God's designation of when the moment for response shall be.

This is why being the first of the four fasts is so significant. The tenth of Tevet inaugurates the entire sequence—it's the initial moment when the trajectory is set, when the decree begins to take form. As the first appointed time for response in this cycle, it embodies God's intentional structuring of when and how we can address the root causes of destruction. If we move this foundational moment that Heaven has deliberately designated, we lose the connection to the entire divinely-structured spiritual framework of the four fasts.

The Annual Decree

The Chatam Sofer offers a striking interpretation transforming our understanding of the tenth of Tevet's contemporary significance. He suggests that on this date each year, a heavenly decree is issued determining whether the Temple will be rebuilt or whether we will once again mourn its absence on the coming Tisha B'Av. (Sidur Chatam Sofer, Peirush to Selichot of Asarah B’Tevet, quoted in Imrei Baruch, VaYigash, #2.)

This transforms the fast from purely commemorative to actively consequential. We don't merely remember that the siege began millennia ago. This date carries ongoing spiritual significance: when judgment commences each year, when our worthiness for redemption faces scrutiny, when the trajectory for the coming year is established.

The fast resembles ta'anit chalom not only structurally but essentially. We fast because this day determines our future, because repentance on this date can avert the decree, because "this very day" carries weight that cannot be transferred. The requirement to fast "on this very day" reflects not merely historical commemoration but ongoing spiritual reality. The day itself matters because judgment occurs on this date. Postponing the fast would mean missing the moment when our response can influence the decree.

The Source in Yosef's Sale

What generated this date's negative spiritual potential? R. Shlomo Fischer (Beit Yishai, 30) citing earlier tradition, suggests the brothers sold Joseph on the tenth of Tevet. When the Babylonian king laid siege to Jerusalem centuries later, the event occurred on the anniversary of the sin that made destruction possible. The Talmud teaches that Jerusalem was destroyed because of baseless hatred among Jews. The siege's commencement on the tenth of Tevet wasn't coincidental; it reflected spiritual reality.

This transforms the fast's meaning. We're not merely commemorating historical events but addressing the ongoing spiritual reality this date represents. The same dynamics that led brothers to sell Yosef—jealousy, hatred, failure of empathy, breakdown of unity—continue to threaten Jewish existence. Each year on this date, we face the question: will we repeat the pattern or transform it?

Each tenth of Tevet, we face judgment not about abstract worthiness but about the specific issue that generated destruction: our relationships with one another, our capacity for unity despite differences, our success in overcoming the baseless hatred that destroyed the Temple and sent us into exile.

The Path Forward

This framework illuminates why the tenth of Tevet might be the one fast that theoretically cannot be postponed. It's not that this fast mourns deeper losses—clearly Tisha B'Av mourns greater tragedies. Rather, this fast possesses unique temporal significance. It marks the beginning of trajectory, the moment of judgment, the anniversary of the foundational breach in unity. As the first of the four fasts, it establishes the framework for all that follows.

Therefore, this day requires our response not merely through memory but through transformation. We fast not only remembering the past but attempting to redirect the future. The day itself matters because judgment occurs now, the decree is issued today, the trajectory is established on this date—and specifically on this date, as the divinely appointed moment for this response.

Joseph's brothers eventually achieved teshuvah. The very family dynamic that generated the sale was transformed. Judah, who proposed selling Joseph, later offered himself as a slave to save Benjamin. The brothers who once showed no empathy ultimately demonstrated complete selflessness. The family that fractured through hatred reunited through love.

Their story demonstrates that trajectories can be redirected. Beginnings don't determine endings. The decree issued on the tenth of Tevet—whether in ancient times or this very year—isn't final. It can be overturned through genuine repentance, through reconstruction of unity, through transformation of the very dynamics that generated destruction.

"On this very day"—the phrase designates a divinely appointed moment that cannot be transferred. The tenth of Tevet, as the first of the four fasts, marks when everything began: when brothers' unity shattered, when siege commenced, when the trajectory toward destruction was established. Standing at that beginning each year, we face the opportunity to choose differently—to transform baseless hatred into unity, to redirect judgment toward mercy, to convert the commencement of catastrophe into the rebirth of redemption.