1) DERIVING THE LAWS OF "INUY" FROM THE LAWS OF "MELACHAH"
QUESTION: The Gemara seeks a source to show that there is no Azharah ("Lo Ta'aseh") against transgressing the prohibitions of Inuy during the period of Tosefes Yom Kippur (for example, one who eats during the time added from the weekday to Yom Kippur at either the beginning or the end of the day does not transgress mid'Oraisa). The Gemara suggests the following Kal v'Chomer based on the Isur of Melachah (which is more "Chamur," or severe, because it is prohibited not only on Yom Kippur but also on Shabbos and Yom Tov): If there is no Azharah for Melachah done during the time of Tosefes Yom Kippur, then certainly Inuy -- which is less severe because it applies only on Yom Kippur -- is not prohibited by an Azharah during Tosefes Yom Kippur.
However, the basis for this Kal v'Chomer is flawed. The Gemara a few lines later says that Inuy is more severe than Melachah in one respect. It is not "Hutar mi'Kelalo" (there is never an allowance to transgress the prohibitions of Inuy). Melachah, on the other hand, is "Hutar mi'Kelalo" (for example, Melachah may be done in order to offer the Korbanos). Consequently, perhaps Tosefes Inuy is prohibited by an Azharah, even though Tosefes Melachah is not. (TOSFOS YOM HA'KIPURIM and RASHASH)
(a) The RASHASH suggests that the fact that Inuy is not "Hutar mi'Kelalo" shows that it carries a more severe punishment and is a weightier prohibition. However, with regard to the question of when the prohibition applies (as opposed to the question of whether an Isur exists altogether), the fact that it is prohibited on fewer days overrides the severity of not being "Hutar mi'Kelalo." As far as time is concerned (whether there is an Azharah for Inuy during the time of Tosefes Yom Kippur), the logic that Melachah applies on more days reveals that the prohibition of Melachah should also apply for more of the day, such as during the time of Tosefes Yom Kippur.
(b) The KORBAN AHARON cited by the TOSFOS YOM HA'KIPURIM says that the source that there is no Azharah for Tosefes Inuy is not really a Kal v'Chomer. The Gemara intends merely to compare Inuy to Melachah. It does not intend to make a real Kal v'Chomer. The Gemara's reasoning is as follows:
The Gemara concludes that the source for the Azharah of Inuy (that is, during Yom Kippur itself) is derived from a Gezeirah Shavah from Melachah ("Etzem-Etzem"), as Ravina teaches. Since the Azharah of Inuy is derived from Melachah, there cannot exist an Azharah for Tosefes Inuy if there is no such Azharah for Tosefes Melachah (as the Beraisa already proved).
2) DERIVING THE PUNISHMENT FOR "MELACHAH" FROM "INUY"
QUESTION: In an attempt to find the source for the Azharah of the Inuyim on Yom Kippur, the Gemara suggests that the verse which states the punishment for doing Melachah on Yom Kippur seems superfluous. This punishment could have been derived through a Kal v'Chomer: The Torah specifies that Inuy is punishable with Kares, even though Inuy applies only on Yom Kippur and not on any other day. Therefore, Melachah certainly is punishable with Kares, for Melachah is more severe than Inuy because it applies on every Shabbos and Yom Tov. Once the Gemara shows that the verse is not needed to teach the punishment for Melachah on Yom Kippur, it instead derives the Azharah for Inuy from the verse.
Since there is a rule that "Ein Onshin Min ha'Din" -- a punishment for a transgression cannot be derived from a Kal v'Chomer, even a punishment like Kares (Tosfos to Chulin 115b, and as implied by the Gemara in Makos 5b), how can the Gemara suggest that the punishment of Kares for Melachah is derived from this Kal v'Chomer? (SI'ACH YITZCHAK)
(a) TOSFOS YOM HA'KIPURIM answers that the Gemara here is in accordance with the opinion in Sanhedrin which says "Onshin Min ha'Din" -- a punishment may be derived from a Kal v'Chomer.
(b) The SI'ACH YITZCHAK answers that the Gemara indeed could have asked how the opinion that maintains "Ein Onshin Min ha'Din" would explain this Kal v'Chomer, but it had a better question to ask. It asks that the Kal v'Chomer itself is incorrect, because Inuy is actually more severe than Melachah since it is not "Hutar mi'Kelalo.".
3) DERIVING THE WARNING AND PUNISHMENT FOR YOM KIPPUR FROM THE WORD "SHABBOS"
QUESTION: Rav Papa learns that the Azharah (warning) for Inuy is derived from the fact that Yom Kippur is referred to as "Shabbos." Just as the Torah gives an Azharah and a punishment for the desecration of Shabbos, so, too, the Torah gives an Azharah and a punishment for the transgression of the prohibition of Inuy on Yom Kippur.
According to Rav Papa, why does the verse specifically state the punishment (Kares) for one who transgresses the prohibition of Inuy? Since the Azharah for Inuy is derived from the fact that Yom Kippur is called "Shabbos," the punishment should also be derived from there, and there is no need for the verse to teach the punishment for Inuy on Yom Kippur.
Furthermore, because Yom Kippur is called "Shabbos," the punishment for its transgression should be Sekilah and not Kares. Why does the verse state that the punishment for Inuy on Yom Kippur is Kares? (This question is asked by the RASHASH.)
ANSWER: The second question answers the first. The Torah needs to write the punishment for transgressing the prohibition of Inuy and it cannot derive it from the fact that Yom Kippur is called "Shabbos," because its punishment is different from that of Shabbos. The Torah teaches that the punishment for Yom Kippur is Kares, while for Shabbos it is Sekilah. Had the Torah not taught that the punishment for transgressing the prohibition of Inuy on Yom Kippur is Kares, a different punishment (Sekilah) would have been derived from Shabbos.
(See Rashi, DH Hi Gufah, who writes that Yom Kippur is like Shabbos "for both its punishment and its Azharah." Why does Rashi mention that Yom Kippur is like Shabbos for "its punishment," if its punishment differs from that of Shabbos? Apparently Rashi means that although the punishment of Yom Kippur could have been derived from Shabbos, nevertheless the verse states the punishment for Inuy on Yom Kippur explicitly. This implies that the punishment should not be derived from Shabbos (Sekilah). Rather, the punishment is Kares.)
4) AGADAH: THE OBLIGATION TO EAT ON EREV YOM KIPPUR
QUESTION: The Gemara derives from the verses that one who eats and drinks on the ninth of Tishrei, the day before Yom Kippur, is considered as though he fasts on both the ninth and the tenth.
Why should eating on Erev Yom Kippur be considered like fasting?
(a) RASHI (DH Kol ha'Ochel) explains that by eating and drinking on the day before Yom Kippur one prepares himself for the fast. Since it is in preparation for the fast of the tenth, his eating is considered to be a part of his fasting. This is also the opinion of the ROSH (Yoma 8:22), and support can be found for it in the Yerushalmi.
(b) The SHIBOLEI HA'LEKET, in the name of RABEINU YESHAYAH, says that it is especially difficult to fast after one has eaten and drunk a lot on the day before the fast. Therefore, one is rewarded for eating on the ninth as if he lengthened his fast of the tenth. (Support for this understanding can be adduced from the Gemara in Ta'anis (26a) which says that fast-days are not established on Sundays, for it is too difficult to fast after a day of festivity. See Pardes Yosef, Vayikra.)
(c) The TUR (OC 604) quotes a story from the Midrash of a simple Jew who outbid the king's officer to buy a fish on the day before Yom Kippur. The Jew later explained to the king that he wanted the fish "to celebrate that Hash-m is going to pardon the sins of the Jewish people" the next day. This demonstrates that eating on the day before Yom Kippur shows one's faith that the fast of the following day will earn him a complete pardon. RABEINU YONAH (Sha'arei Teshuvah 4:8) also suggests such an explanation.
(d) Since Yom Kippur is a Yom Tov, it requires a Se'udas Yom Tov, a festive meal. However, one cannot have a Se'udah on Yom Kippur because of the obligation to fast. The Se'udah, therefore, was moved to the ninth. Since the Se'udah of the ninth is part of the celebration of the tenth, one who eats on the ninth is considered to have fasted on both days. (Rabeinu Yonah, Sha'arei Teshuvah 4:9)
(e) The ARUCH LA'NER (Rosh Hashanah 9a) suggests a novel approach. During the year, a person sins with both his body and his soul. One who fasts on Yom Kippur afflicts his body in order to attain atonement for the sins he committed with his body against his soul. When he eats on the day before Yom Kippur, he afflicts his soul in order to atone for the sins he committed with his soul against his body (such as excessive fasting on days when one is not required to fast).
All of these reasons assume that the Mitzvah to eat on the ninth of Tishrei is related to the fast of atonement on the tenth. Consequently, one may conclude that women are also obligated to eat on the ninth of Tishrei, even though it is a time-dependent obligation from which women are normally exempt. Since women must fast on Yom Kippur, they are also required to do everything connected with that fast, which should include eating on the ninth. This is how the MAHARIL rules as cited by the DARCHEI MOSHE (OC 604:1). (See also REBBI AKIVA EIGER, Teshuvos 1:16, and KESAV SOFER, Teshuvos OC 112).