1) HALACHAH: BENEFITING FROM A MELACHAH PERFORMED BY A JEW ON SHABBOS
OPINIONS: The Tana'im disagree about whether one may benefit from the result of a Melachah performed by a Jew on Shabbos. Rebbi Meir maintains that food cooked on Shabbos accidentally (b'Shogeg) may be eaten on Shabbos by anyone, even the person who cooked it. Food cooked intentionally (b'Mezid) may not be eaten on Shabbos by anyone, but it may be eaten after Shabbos.
Rebbi Yehudah maintains that food cooked on Shabbos b'Shogeg may be eaten only after Shabbos, by anyone. Food cooked b'Mezid may never be eaten by the person who cooked it, but it may be eaten after Shabbos by one who did not cook it.
Rebbi Yochanan ha'Sandlar rules that the transgressor may never eat food he cooked on Shabbos, whether he cooked b'Shogeg or b'Mezid. Others, however, may eat the food after Shabbos if it was cooked b'Shogeg. If it was cooked b'Mezid others may never eat it.
The Gemara in a number of places (see, for example, Shabbos 18b, 151a) teaches that when a Jew wrongfully instructs a Nochri to perform Melachah on Shabbos, the Jew may not benefit from that Melachah until "bi'Chedei she'Ya'asu" -- until enough time has passed for the Melachah to be done after Shabbos. When the Tana'im here rule that one may not benefit from Melachah wrongfully performed by a Jew on Shabbos, do they require that one wait "bi'Chedei she'Ya'asu" or do they permit one to benefit from the Melachah immediately after Shabbos?
(a) RASHI in Chulin (15a, DH Lo Yochal) writes that one must wait "bi'Chedei she'Ya'asu" whenever he is required to wait until after Shabbos to eat the food. Since one may not benefit from a Melachah performed on Shabbos, he obviously must wait "bi'Chedei she'Ya'asu." This is also the opinion of the BEHAG (Hilchos Shabbos 22b) and the RAMBAN. The Ramban adds that this requirement applies only to a Melachah which was performed wrongfully by a Jew, but not to a Melachah which was permitted on Shabbos because of Piku'ach Nefesh. A vegetable picked on Shabbos for a deathly-ill person may be eaten by a healthy person immediately after Shabbos.
(b) However, the RAMBAM (Hilchos Shabbos 6:23) rules that when a Jew performs Melachah from which one may benefit after Shabbos, he is permitted to benefit from it immediately after Shabbos. This is also the opinion of RABEINU YONAH (cited by the MAGID MISHNEH), the ROSH, RAN, and many other Rishonim (see BEIS YOSEF OC 318:1).
Why, according to the ruling of these Rishonim, is the Halachah more stringent with regard to a Melachah performed by a Nochri for a Jew on Shabbos (which constitutes an Isur d'Rabanan according to most opinions) than with regard to a Melachah performed by a Jew on Shabbos (which is an Isur d'Oraisa)?
The BEIS YOSEF and others explain that the reason why the Halachah is more stringent with regard to a Melachah performed by a Nochri is that people tend to be more lax with the prohibition against benefiting from a Nochri's Melachah, since it is only mid'Rabanan. If one would be allowed to benefit from a Nochri's Melachah immediately after Shabbos, he might openly ask the Nochri to do Melachah for him on Shabbos. In contrast, when a Jew accidentally does Melachah on Shabbos, there is no concern that if he is permitted to benefit from the Melachah immediately after Shabbos he will do Melachah on Shabbos again. Also, there is no concern that a Jew will tell another Jew to do Melachah for him on Shabbos. Therefore, there is no requirement to wait "bi'Chedei she'Ya'asu" in order to benefit from a Melachah done by a Jew on Shabbos.
The SHITAH MEKUBETZES in Chulin (15a) points out that there is a case in which waiting "bi'Chedei she'Ya'asu" is necessary in order to permit one to benefit from a Melachah done by a Jew. The Gemara in Shabbos (18b) discusses a case in which a woman filled a pot with legumes and put it in the oven right before Shabbos, and thereby transgressed the Isur d'Rabanan of Shehiyah. The Gemara rules that one is permitted to benefit from the legumes after Shabbos, but only after he waits "bi'Chedei she'Ya'asu." How does the Rambam (and other Rishonim) understand the Gemara there?
The Shitah Mekubetzes answers that when a person performs a Melachah before Shabbos and the effects of that Melachah occur on Shabbos, it is not obvious to everyone that benefiting from the Melachah is prohibited (or that the Melachah itself is even prohibited to do in the first place). Therefore, the Rabanan were stringent in such a case and instituted the requirement to wait "bi'Chedei she'Ya'asu," just as they were stringent and prohibited benefiting from Melachah performed by a Nochri on Shabbos. The Isur that was done is not so obvious, and thus there is a concern that people might continue to do this form of Melachah on Shabbos. The Rabanan instituted the requirement to wait "bi'Chedei she'Ya'asu" so that it would be clear to everyone that such a Melachah is forbidden.
HALACHAH: The TUR and SHULCHAN ARUCH (OC 318:1) rule like the Rambam and permit one to benefit, immediately after Shabbos, from Melachah done by a Jew on Shabbos. The MISHNAH BERURAH (318:5) also records the opinion of the Rambam. However, the Halachah may differ in the case of a Melachah done by a non-observant Jew who has no reservations about violating Shabbos. Even the Rambam may agree that one may not benefit from such a Jew's Melachah until after he waits "bi'Chedei she'Ya'asu." (See HE'OROS B'MASECHES CHULIN, 15a, in the name of RAV Y. S. ELYASHIV shlit'a.) (Y. MONTROSE)
2) INADVERTENT THEFT
QUESTION: Rava rules that when a man dies and leaves his children a borrowed cow, the children may use the cow for the duration of time for which their father had borrowed it. If the cow dies through an Ones (circumstances beyond one's control), the heirs are not responsible for it. Although a borrower generally is obligated to pay the owner for the animal he borrowed even when the it died through an Ones, his heirs do not have to pay because they did not borrow the cow themselves (Rashi DH Ein).
If the children slaughtered and ate the cow under the erroneous assumption that the cow belonged to their father, they are obligated to pay to the original owner only the lowest market price for the value of the meat. (Rashi here (DH Demei) and the RASHBAM in Bava Basra (146b, DH v'Shamin) explain that this means that they must pay only two thirds of the meat's actual value.]
Why are the heirs not obligated to pay the full price of the meat they ate? In what way does this case differ from the case of the Gemara in Bava Kama (111b) in which a person stole an object and, before the owners despaired ("Ye'ush") of recovering it, someone else came and ate the object? In that case, the owner may collect the value of the object either from the original thief or from the person who ate it. In the case of the Gemara here, there is no indication that the owner despaired (just because the borrower died), and thus the children should be required to pay the full value of the meat to the owner and not a reduced value.
ANSWER: The RITVA, RA'AVAD, and other Rishonim explain that the difference between the two cases is the person's awareness of the fact that he is stealing. In the case in Bava Kama, the person who eats the meat knows that the meat was stolen by a thief. Even if he does not know that it was stolen, he himself intends to steal it from the thief. In contrast, in the case of the Gemara here the heirs think the cow belonged to their father and they think they are eating meat rightfully belongs to them. Since that they are not deliberately stealing, they are not required to pay the full price.
The MACHANEH EFRAIM (Hilchos Gezeilah #7) writes that the Ritva clearly implies that one who steals inadvertently is not categorized as a Gazlan (thief).
(The RASHBAM (Bava Basra 146b, DH v'Shamin) writes that the law that one pays only for inexpensive meat, or two thirds of the actual value, applies in any case in which one person eats the food of another person which he would not have eaten had he known that he would have had to pay for it. See RE'AH here who writes that this value represents the benefit that the eater derived from the meat, rather than its actual market value.)
According to this approach, the Ritva explains the Gemara earlier (30b) which states that when one person thrusts food down another person's throat, the second person is considered to be the thief. The Ritva explains that the Gemara refers specifically to a case in which the second person knows that the food does not belong to the person who gives it to him. For this reason the Gemara there says he is a thief only if he could have cast it out of his mouth but did not. If he did not know at the time he ate it that it was stolen, he is not considered a thief. (D. BLOOM)