1) EATING BEFORE AND AFTER A "TA'ANIS SHA'OS"
OPINIONS: Rav Chisda states that a Ta'anis Sha'os is a valid Ta'anis only when the person does not eat anything until nightfall.
If a Ta'anis Sha'os is when one does not eat for the entire day, in what way does a Ta'anis Sha'os differ from an ordinary Ta'anis?
(a) RASHI says that although a person who observes a Ta'anis Sha'os does not eat all day, his Ta'anis differs from an ordinary Ta'anis in that he did not accept upon himself the Ta'anis the day before. Only during the day that he actually fasted did he decide to formally accept upon himself the day as a fast. In contrast, when one accepts the Ta'anis the day before, his fast is an ordinary Ta'anis. (See Insights to Ta'anis 11:2:a.)
(b) The RAMBAN and RITVA cite the Yerushalmi which says explicitly that a person may observe a Ta'anis Sha'os even after he ate cheese and drank water. They explain that when the Gemara here says that a person may not eat anything on the day of a Ta'anis Sha'os, it means that one may not eat anything as a Se'udas Keva, a normal meal. One may, however, taste foods and then start his Ta'anis Sha'os afterwards, as the Yerushalmi implies.
When Rav Chisda says that one may not taste anything on a Ta'anis Sha'os until nightfall, he means that one may not taste anything after he starts to fast. He may taste something before he starts to fast.
(c) The RAN also rules like the Yerushalmi and says that one may eat on the day of a Ta'anis Sha'os before the Ta'anis begins. In contrast to the view of the Ramban and Ritva, however, he does not differentiate between tasting food (a snack) and eating a full meal. This is also the ruling of the RAMBAM (Hilchos Ta'anis 1:13). The Ran and Rambam maintain that Rav Chisda discusses only the obligation to fast after one starts the Ta'anis Sha'os until nightfall. He does not mean that one must fast from daybreak until the time of his Ta'anis Sha'os.
(d) The Yerushalmi cited by the Rishonim adds another point. Not only is one permitted to eat before the Ta'anis Sha'os, but one may even observe a Ta'anis Sha'os during the first half of the day and eat after the Ta'anis, during the second half of the day.
The Yerushalmi's allowance seems to contradict the Gemara here which says that one must fast until nightfall. The ROSH (1:12) and TOSFOS (Avodah Zarah 34a) suggest that perhaps the Gemara here and the Yerushalmi do not disagree, and that the Gemara here also maintains that one may eat before nightfall after he observes a Ta'anis Sha'os during the first part of the day. When Rav Chisda says that one must fast until nightfall, he means that l'Chatchilah if one wants to experience the severity of a Ta'anis properly (in order to recite Aneinu), he must refrain from eating until nightfall. However, even if he accepts only to fast until midday and he plans to eat afterwards, his word is still binding because a half-day fast is also considered a fast with regard to his obligation to fast until the time he stipulated.
(This is in contrast to what Rashi writes numerous times throughout the Sugya, that when one accepts to fast for only part of a day, his Kabalah is not considered a "Nidrei Mitzvah" at all and is not binding. See Rashi DH l'Tze'urei Nafshei.)
(e) The TERUMAS HA'DESHEN (#157) asserts that when one accepts to fast until midday and to eat afterwards, even Rav Chisda would agree that his fast is a full-fledged Ta'anis Sha'os and that he must recite Aneinu. Rav Chisda maintains that one must fast until nightfall only when he accepted upon himself to fast for an entire day. If he accepted only a Ta'anis Sha'os, he may eat after the Ta'anis Sha'os is over, as the Yerushalmi says.
HALACHAH: The SHULCHAN ARUCH (OC 562:1) cites the Gemara here which says that one who accepts a Ta'anis only until midday does not recite Aneinu. The Shulchan Aruch (562:11) rules like the ROSH and says that although one does not recite Aneinu, he is required to fulfill his pledge to fast until midday (or from midday until nightfall), but he may eat during the rest of the day.
The REMA (562:1) says that one should take into account the opinion of the TERUMAS HA'DESHEN who rules that one recites Aneinu even if he accepted to fast only until midday and plans to eat after that. Therefore, one should recite Aneinu in the blessing of "Shome'a Tefilah" on such a fast. The MISHNAH BERURAH (562:6) adds that this applies only if one recites Minchah before he ends his fast. If he eats before Minchah, he does not recite Aneinu even according to the Terumas ha'Deshen.
2) ACCEPTING UPON ONESELF A "TA'ANIS SHA'OS"
QUESTION: Shmuel says that if one does not formally accept upon himself to fast the day before he intends to fast, his fast is not a valid Ta'anis. The Gemara earlier (11b), however, discusses a "Ta'anis Sha'os," a fast which one observes without accepting it the day before (as Rashi explains there), which is nonetheless a valid Ta'anis.
According to Shmuel, such a fast should not be a valid Ta'anis since the person did not accept it upon himself the day before. How are these two statements of the Gemara to be reconciled?
ANSWERS:
(a) The RITVA and RAN explain that Shmuel emphasizes that one must accept upon himself the Ta'anis before he begins to fast, but he does not necessarily have to accept it the day before he fasts. A Ta'anis Sha'os also needs a Kabalah, but it does not need to be done the day before the fast. Shmuel refers to an ordinary Ta'anis, when one accepts upon himself to fast the entire day. In the case of an ordinary Ta'anis, the person must accept the fast on the previous day.
(b) TOSFOS in Avodah Zarah (34a) and the ROSH (1:12) indeed rule that one must accept the Ta'anis Sha'os the day before (see Insights to Ta'anis 11:2). This is easy to understand according to the Yerushalmi which says that a partial Ta'anis (Ta'anis Sha'os) is acceptable even when one eats on the same day as the Ta'anis (before it starts or after it finishes). One may accept upon himself, on the preceding day, to observe a Ta'anis Sha'os which will last for only a few hours, and he may eat until the time at which his fast starts.
However, according to those Rishonim (such as Rashi) who explain that a Ta'anis Sha'os refers to a full-day fast without a formal Kabalah the day before, how is it possible to accept upon oneself, the day before, to observe a Ta'anis Sha'os on the following day? By definition, the fast is a Ta'anis Sha'os only when one does not accept it the day before!
Tosfos in Avodah Zarah explains that even according to those Rishonim, it is possible for a person to accept upon himself a Ta'anis Sha'os on the previous day. The person can accept upon himself that if he does not eat (for whatever reason) the next day until midday, then now he accepts upon himself to fast from midday tomorrow until the end of the day. In such a case, he fasts the entire day with a Kabalas Ta'anis, but without accepting upon himself to fast the entire day.
(c) Tosfos and the Rosh cite RABEINU TAM who says that Shmuel requires a Kabalah only l'Chatchilah. The Kabalah makes a person's fast into a valid, full-fledged Ta'anis. Even without a Kabalah, however, his fast is still considered a valid Ta'anis (and he fulfills his obligation to fast, and perhaps he may even recite Aneinu). When the Gemara says that one who fasts without a Kabalah is like a "blown-up sack," it means that he must repent for the misdeed of afflicting himself without a formal acceptance of the Ta'anis.
(d) The RIF omits the entire Sugya of Ta'anis Sha'os. The RAN suggests that the Rif may have understood that Shmuel argues with Rav Huna and with those who say that a Ta'anis Sha'os is a valid Ta'anis, and he rules like Shmuel that there is no such thing as a Ta'anis Sha'os. One must accept upon himself his fast the day before, and there is no partial Ta'anis.
HALACHAH: The SHULCHAN ARUCH (OC 562:5) rules like Shmuel who says that one must accept upon himself a Ta'anis the day before. He cites two opinions ((a) and (b) above) with regard to whether a Ta'anis Sha'os requires a Kabalah the day before or not (562:10). The REMA (562:5) cites the opinion of Rabeinu Tam who says that the requirement to accept the Ta'anis is only l'Chatchilah, and even if one did not formally accept to fast he may still recite Aneinu. (The MISHNAH BERURAH adds that one may recite Aneinu when he fasts without a Kabalah only if he fasts for the entire day, but not if he fasts for only part of the day. However, he still may recite Aneinu without the words "Yom Tzom Ta'anisenu.")
In the case of a Ta'anis Chalom (a fast for a bad dream), everyone agrees that no Kabalah is necessary and one may recite Aneinu.
3) "YE'ASER" OR "YEYASER"?
QUESTION: The Gemara records a dispute between Rav and Shmuel about when one must accept upon himself a Ta'anis. Rav maintains that one may accept the Ta'anis at any time before the day of the Ta'anis. Shmuel maintains that one must accept the Ta'anis specifically in the Minchah Shemoneh Esreh on the day before the Ta'anis.
The Gemara cites support for Shmuel's view from a Beraisa in Megilas Ta'anis. After the Beraisa lists the days on which fasting is prohibited, it says that "any person who accepted upon himself from before those days, Yeyaser." RASHI explains that "Yeyaser" means that the person must "make himself prohibited" from eating by accepting the "Ta'anis" again before the day of the Ta'anis. Even though he already accepted upon himself to fast, his initial Kabalah did not make the Ta'anis binding enough to override the Yom Tov of Megilas Ta'anis. Only if he formally accepts upon himself again -- with the wording of an oath -- to fast is his Kabalah considered strong enough to override the Yom Tov. The Gemara infers from this Beraisa support for the view of Shmuel who maintains that one must accept the Ta'anis during the Minchah Shemoneh Esreh.
In defense of Rav, the Gemara cites another version of the Beraisa which reads "Ye'aser" instead of "Yeyaser." "Ye'aser" means that "he will be prohibited" from eating because he accepted upon himself to fast. The Gemara asks that according to this version of the Beraisa, what new law does the Beraisa teach? It is obvious that one becomes prohibited from eating when he accepts upon himself to fast! The Gemara answers that the Beraisa teaches that the status of his Ta'anis depends on when he accepted the fast: if he accepted the fast before the Chachamim declared that day a Yom Tov, his oath to fast is binding. If he accepted to fast after the Chachamim declared that day a Yom Tov, his oath is not binding and his fast is not observed.
A number of points in the Gemara need clarification. First, what is the Gemara's proof from the Beraisa for Shmuel's opinion? While the Beraisa does indicate that one's acceptance of the Ta'anis must be made in advance, how does the Beraisa prove that it must be made in the Minchah Shemoneh Esreh before the Ta'anis?
Second, why does the Gemara explain -- according to the version of the Beraisa which reads "Ye'aser" -- that the status of the Ta'anis depends on when the person accepted the Ta'anis? What difficulty does the Gemara have with the Beraisa such that it needs to give additional details in order to understand it? Why does the Beraisa become less clear if it says "Ye'aser" and not "Yeyaser"? The Beraisa still teaches something new, because one would have assumed that he is not required to fast when he accepts upon himself to fast on one of the days mentioned in Megilas Ta'anis. Since those days were instituted as days of celebration, one might have thought that even if he accepted upon himself to fast on one of those days he is not obligated to fulfill his word (as the Gemara indeed concludes). The Beraisa, therefore, is needed to teach that he nevertheless must fast.
ANSWERS:
(a) According to Rav (who says that one is not required to accept the Ta'anis specifically in the Minchah Shemoneh Esreh), one may accept the Ta'anis any time before the day of the Ta'anis, even months in advance. Just as Rav is lenient and does not require that one accept the Ta'anis in Shemoneh Esreh, he is lenient and does not require that one accept the Ta'anis immediately before it starts. (RITVA)
According to Shmuel, however, one's decision to observe a fast is never binding unless he formally accepts the fast in the Minchah Shemoneh Esreh before the day of the fast, immediately before the fast.
This assumption provides clarity for the proof from the Beraisa for Shmuel's view. Why does the Beraisa say that one who accepted a series of fasts must accept them again ("Yeyaser")? It must be that there is a requirement to accept each Ta'anis immediately before the day of the Ta'anis, as Shmuel says.
When the Gemara cites the version of the Beraisa which says "Ye'aser," it re-explains the Beraisa based on that change. If the Beraisa means merely that the person is prohibited from eating, then why does the Beraisa mention that "if he accepted the Ta'anis from before, he becomes prohibited from eating"? What is the meaning of the words "from before" -- "from before" what? Those words seem irrelevant; the Beraisa should have said that "if he accepted the Ta'anis, he becomes prohibited from eating," without the words "from before."
According to Shmuel, the need for the words "from before" in the Beraisa is clear. Since he accepted the Ta'anis long before the day of the Ta'anis, he must re-accept it right before the Ta'anis. According to Rav, however, what do the words "from before" mean?
The Gemara answers that the Beraisa means that one's Kabalah makes the day into a Ta'anis only when it was proclaimed from before the day became a Yom Tov. If his Kabalah was made after the day became a Yom Tov, he does not have to fast because the celebration overrides the Ta'anis. (-Based on the RAN.)
(b) TOSFOS apparently has the opposite Girsa in the Gemara. Tosfos asserts that the version of the Beraisa which says "Ye'aser" (with an Alef) is proof for Shmuel's opinion because "Ye'aser" means that one has succeeded in prohibiting himself from eating (by making a Kabalah to fast). "Yeyaser," on the other hand, implies that he is "removed" from the obligation to fast -- his Ta'anis is pushed aside by the Yom Tov and he may eat. The Gemara asks what the Beraisa means by this. The Gemara answers that the Beraisa means that the status of the fast depends on when he made his Kabalah: if he made his Kabalah before the Chachamim enacted the day as a Yom Tov, then he must fast, and if he made his Kabalah after the Chachamim enacted the day as a Yom Tov, then he does not fast but rather "Yeyaser" -- he is removed from the obligation to fast.
According to Tosfos, how does the Beraisa support Shmuel's opinion that one must accept the Ta'anis in Minchah the day before? The Beraisa says only that he is prohibited from eating ("Ye'aser"); it says nothing about when he needs to accept the Ta'anis! Moreover, what is the Gemara's question on the version that says "Yeyaser"? Perhaps that version of the Beraisa teaches simply that one's Kabalah to observe a Ta'anis Yachid does not override a Yom Tov of Megilas Ta'anis.
Tosfos' explanation can be understood based on the comments of the HAGAHOS MAIMONIYOS (Hilchos Ta'anis 1:7) who explains the Gemara in the opposite way of Rashi. While Rashi says that the Kabalah for a Ta'anis is more effective when it is made closer to the Ta'anis, the Hagahos Maimoniyos says that the Kabalah for a Ta'anis is more effective the earlier it is made. The Hagahos Maimoniyos quotes the RA'AVYAH who says that it is better to make the Kabalah long before the day of the Ta'anis. Shmuel says that even a "weak" Kabalah -- one made close to the Ta'anis -- suffices, even if it is made immediately before the Ta'anis begins (in the Minchah Shemoneh Esreh of the day before). Rav is more stringent and requires that the Kabalah be made before the Minchah Shemoneh Esreh of the day before the Ta'anis.
The inference from the Beraisa in Megilas Ta'anis may be based on the words, "if he accepted the Ta'anis from before...." The words "from before" seem extra. Apparently, they teach that from any time before the day of the Ta'anis, the Kabalah is valid (as Shmuel says), even if it is made only a very short time before the Ta'anis. Thus, the Beraisa supports Shmuel.
The Gemara then cites the version of the Beraisa which reads "Yeyaser," which means that one does not need to fast. The Gemara asks what do the words "from before" mean according to this text of the Beraisa. If the Beraisa intends to teach that the Ta'anis never overrides the Yom Tov, what difference does it make whether the Kabalah was made immediately before the Ta'anis or much earlier? Even if the Kabalah was made earlier, the Ta'anis should not override the Yom Tov.
The Gemara answers that the Beraisa teaches that if one makes his Kabalah shortly before the Yom Tov arrives, when the Chachamim had already instituted that day to be a Yom Tov before his Kabalah, then "Yeyaser" -- his obligation to fast "is removed." If, however, he accepted the Ta'anis long before the Yom Tov (i.e. before the Yom Tov was even instituted), the Ta'anis remains binding. (M. KORNFELD)

12b----------------------------------------12b

4) "BORROWING" A TA'ANIS AND "PAYING IT BACK"
QUESTION: Rav says that one may "borrow" a Ta'anis from one day and "pay it back" to another day ("Loveh u'Pore'a"). That is, if one pledged to fast on a certain day but was unable to fast when that day arrived, he may make it up on another day.
According to the Gemara's first version of the dialogue, Shmuel disagrees with Rav and says that when a person accepted upon himself to fast and then found himself unable to fast on the designated day, he does not have to fast and he is not required to make it up on another day because he never made a Neder (a vow) to fast. According to the Gemara's second version, Shmuel agrees with Rav that one must make up the fast on another day if he does not fast on the day he designated as a Ta'anis.
Why is a person's Kabalah to fast not considered a Neder? His Kabalah should be binding like a Neder and he should not be permitted to delay its fulfillment by fasting on a different day.
Moreover, why does Shmuel say (in the Gemara's first version) that one who finds it difficult to fast is not required to fast and is not required to make it up on a different day? Why is his Kabalah not binding?
ANSWERS:
(a) The RAMBAM (Hilchos Nedarim 4:16) explains that Rav's statement refers only to a case in which one accepted to fast a certain number of fasts but did not specify on what days those fasts would occur. He began to fast on a day he thought would be a good day on which to fulfill one of his fasts, but as the day progressed he discovered that it was not a good day to fast (for example, he was invited to a Se'udas Mitzvah, or it became very hot and he was weak). In such a case he may "borrow and pay back" because he never accepted upon himself to observe a fast specifically on this day. (According to the Rambam, an acceptance to fast without specifying the day is considered a valid Kabalah for the Ta'anis.) The Rambam's explanation is based on the Yerushalmi, as cited by the Ran.
This approach explains the view of Rav. Why, though, does Shmuel say that the person's Kabalah is not binding at all, and if one cannot fast on the day he intended he does not have to fast or make up for it? Since he made an oath to fast for a certain number of days, he must fulfill his word and complete that number of fasts. If he does not make up for this day, he fails to fulfill his word to fast for a specific number of days.
The answer is that the Rambam learns like the BA'AL HA'TZEROROS (see also RABEINU CHANANEL) who says that the Gemara refers to a case in which the person fasted part of the day and then he needed to stop. The physical distress that he experienced from his partial fast counts as a day of Ta'anis to fulfill his Neder. Rav argues and says that he must make up his fast on another day because his Kabalah was to fast a full day.
(b) The ROSH explains that according to Rav, when the person originally accepted to fast he did not accept the fast with the terminology of a Neder or Shevu'ah. Rather, he merely said that he accepts upon himself to fast. He is obligated to fast not because of a Neder but because of his Kabalah to do a Mitzvah. When a person makes a Kabalas Mitzvah to fast, he presumably has in mind to fulfill the Mitzvah of fasting whenever he has the opportunity, and he leaves himself the option to choose a different day on which to fast if the day he originally designated turns out to be inconvenient.
The Rosh cites the RA'AVAD who quotes the Gemara in Erchin (7a) which says that when one makes a Neder to give certain coins to a charity, he may change his mind and give different coins until the treasurer comes and takes the actual coins which he promised to give. The NIMUKEI YOSEF here explains that this is based on the same principle as a Kabalas Mitzvah to fast: when a person makes a Neder of Nidrei Mitzvah, he presumably intends to retain the right to do the Mitzvah at a different time or with a different object if the need arises.
According to the Rosh, Rav refers even to a case in which one specifies a date for the Ta'anis (in contrast to the opinion of the Rambam). He may still "borrow" the Ta'anis from that day and "pay it back" on another day, because that was his original intention.
Shmuel extends this condition and says that if a person sees that it is too difficult for him to fast on this day, not only is he not required to fast on that day, but he is also not required to make up the fast on another day. Shmuel's reason is because it is assumed that the person had in mind at the time of his Neder to fast only if he would be able to fast.
HALACHAH: The Halachah follows the view of Rav, in accordance with the principle that in any argument between Rav and Shmuel which involves a non-monetary matter, the Halachah follows the view of Rav. The SHULCHAN ARUCH (OC 568:2) rules like the Rambam's understanding of Rav, that when one accepted upon himself to fast a certain number of days but did not specify which days, he may change his mind on a day on which he begins to fast if he realizes that he will not be able to fast that day, and he may make it up on another day. However, one may do this only if there is a strong reason not to fast; for example, he was invited to a Bris Milah or to a Siyum, or he was invited to dine with a Torah sage. Being invited to dine with friends is not a valid reason to push off his fast (MISHNAH BERURAH 568:9).
The allowance to push off a fast to another day applies only to a Ta'anis Yachid, but not to Ta'anis Chalom or to a Ta'anis Tzibur (REMA 568:2).

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