QUESTION: The Mishnah states that if a day of fasting was decreed due to a lack of rain and then rain falls during that day of fasting, under certain circumstances (depending on what time of day the rain falls) the fast does not continue. According to the Tana Kama, if the rain falls before sunrise, the fast does not continue. According to Rebbi Eliezer, if the rain falls before midday, the fast does not continue. Instead, the people eat and drink and treat the day like a festive Yom Tov, and in the afternoon they recite Hallel. Once the fast has begun (according to the Tana Kama) or once most of it has passed (according to Rebbi Eliezer), the entire day of fasting must be observed (Yerushalmi). According to this reasoning, if the community accepted an entire series of fasts due to lack of rain, it is clear that there is no need to complete the series of fasts if rain falls.
The Gemara earlier (10b) teaches that if one was in the middle of a fast due to some threat (Tzarah) which then passed, or if one was in the middle of a fast on behalf of a sick person who then recovered, he must complete his fast. In addition, the Rishonim write that the Gemara there implies that if his fast was part of a series of fasts which he had accepted upon himself, he must continue to observe the entire series of fasts (RASHI there and Rishonim; see ME'IRI, however, who disagrees).
What is the difference between the case of the Mishnah here and the case in the Gemara earlier (10b)?
(a) The RA'AVAD (Hilchos Ta'aniyos 1:15) explains that whether or not one must complete the fast depends on the nature of the Tzarah for which one is fasting. Only when one fasts for rain does the fast end when the need ceases on the day of the Ta'anis. The day becomes a day of festivity because the cessation of a drought is cause for great rejoicing. A lack of rain differs from all other types of Tzarah. When rain comes and ends a drought, the threat of famine has ended. In contrast, when one fasts for any other Tzarah (such as disease or disaster), even when the particular threat passes there is still concern that it might return.
The GEVURAS ARI suggests that according to the Ra'avad's reasoning, in the case of other types of Tzarah that end during the fast, one must continue to fast only when the Tzarah stops and relief comes, since there is concern that the Tzarah might return. However, if one fasts on behalf of a sick person and that person dies, the Tzarah has clearly finished and he should stop fasting.
However, this conclusion is questionable. RASHI (10b, DH Al ha'Tzarah) points out that there is another consideration to take into account when the Tzarah ends. If one stops fasting when the Tzarah ends with no salvation, he gives the appearance as though his fast is contingent on Hash-m's response to his prayer; it appears as though he threatens Hash-m that he will continue to fast only if Hash-m sends salvation. Since this is clearly disrespectful to Hash-m, one should continue fasting if a Tzarah ends with no positive outcome.
The ROSH questions the Ra'avad's approach. Why does the Ra'avad say that the coming of rain during a fast day marks the end of the drought (and Tzarah)? One stops fasting even when only a little rain falls, even though it is not enough rain for the entire season. Perhaps no more rain will fall for the rest of the season and the drought will return! (The Ra'avad apparently maintains that such a situation would be considered a "new" drought.)
(b) RASHI (25b, DH v'Yiheyu) and other Rishonim explain that the type of Tzarah for which one fasts makes no difference; all Tzaros are the same when it comes to interrupting the fast day. Rather, the difference is whether one is observing an individual Ta'anis (a Ta'anis Yachid) or a communal Ta'anis (a Ta'anis Tzibur). When one fasts as an individual, he must continue his fast until the end of the day, but when he fasts together with the Tzibur, the fast ends when the Tzarah ends (when it rains).
Several explanations are offered for this difference between a Ta'anis Yachid and a Ta'anis Tzibur.
1. The MAGID MISHNEH (in his first explanation) writes that the Chachamim were lenient with regard to a Ta'anis Tzibur so as not to burden the entire community ("Tircha d'Tzibura").
2. The MAGID MISHNEH (in his second explanation) writes that when Beis Din decrees a Ta'anis for the community, they include a condition that if it rains in the middle of the fast day, the Ta'anis will be annulled. This condition is effective even when Beis Din does not explicitly declare it, because of the principle of "Lev Beis Din Masneh Aleihen" -- unspoken conditions for enactments of Beis Din are fully binding and effective. In contrast, when an individual observes a personal Ta'anis, any condition which he does not verbally express is not binding because "Devarim sheb'Lev Einam Devarim" -- thoughts in one's heart are not binding (until they are verbalized).
3. The ROSH infers a different explanation from the wording of the RAMBAM. When the community observes a Ta'anis Tzibur, they are obligated to recite Hallel ha'Gadol when Hash-m answers their prayers. Since Hallel may be recited only when one is satiated and feels good (26a), the people must stop fasting in order to eat so that they may fulfill their obligation to recite Hallel. An individual, on the other hand, does not recite Hallel when his prayers are answered, and therefore there is no reason for him to stop fasting in the middle of the day.
HALACHAH: The SHULCHAN ARUCH (OC 569) records as the Halachah the answer of Rashi, as explained by the Rosh. The Shulchan Aruch adds, based on the Yerushalmi, that if the Talmidei Chachamim decide to continue fasting nonetheless, the rest of the Tzibur is also obligated to finish the fast.
If it is discovered that the Ta'anis was accepted in error -- that is, the Tzarah ended before the day of the fast, and those who accepted the fast were unaware of it -- then even an individual does not have to complete his fast.
If one was fasting on behalf of a sick person who died during the day of the fast, an individual who was observing a Ta'anis Yachid must complete his fast (as Rashi says on 10b). Whether or not a Tzibur must complete the Ta'anis Tzibur in such a situation is the subject of dispute among the Acharonim (see MISHNAH BERURAH OC 569:5). Some rule that a Tzibur must complete the fast (even if the person for whom they were fasting died before midday), based on the reasoning suggested by the ROSH (that the only reason to stop fasting is in order to say Hallel, which the Tzibur obviously does not say when the person died). Others maintain that the Tzibur may stop the fast because the other two reasons mentioned above (1 and 2) still apply.
The SHA'AR HA'TZIYUN writes that perhaps one should be stringent and complete the fast even though the Tzarah has ended. He writes that even according to the reason that Beis Din makes the fast conditional upon the Tzarah persisting, Beis Din may stipulate that the fast will be annulled only if Hash-m answers their prayers in a positive way. If the Tzarah ends without a clear salvation from Hash-m (such as in the case of the sick person who dies), perhaps the fast is not annulled.