1) MELACHOS DONE FOR A DESTRUCTIVE PURPOSE
QUESTION: The Mishnah (105b) states that one is exempt for all acts of Melachah that he does for a destructive purpose ("Mekalkel"). Rebbi Avahu quotes a Tana who states that the Melachos of Chovel (inflicting a wound) and Mav'ir (kindling a fire) are exceptions for which one is Chayav even when he does the Melachah for a destructive purpose. Rebbi Yochanan argues and maintains that one is Chayav for Chovel and Mav'ir only when there is a constructive element in the perpetrator's act. For example, he is Chayav for Chovel only when he inflicts a wound on an animal in order to obtain blood to feed to his dog, and he is Chayav for Mav'ir only when he kindles a fire because he needs the ashes.
The Gemara questions Rebbi Avahu's opinion from the Mishnah that states that one is exempt for all Melachos done for a destructive purpose. The Gemara answers that the Mishnah follows the opinion of Rebbi Yehudah, while the Tana quoted by Rebbi Avahu follows the opinion of Rebbi Shimon. (From the words of Rashi it seems that Rebbi Yochanan, who argues with Rebbi Avahu, follows the opinion of Rebbi Yehudah, like the Mishnah.)
Rashi explains that according to Rebbi Shimon, it is not possible to perform an act of Mav'ir or Chovel she'Tzerichah l'Gufah for a constructive purpose. This raises the following question. Even though one is Chayav for an act of Mekalkel according to Rebbi Shimon, in order to be Chayav on Shabbos for doing a Melachah another condition must be met. The Melachah must be a Melachah she'Tzerichah l'Gufah (even for Chovel and Mav'ir, Sanhedrin 85a). How can one do an act of Mekalkel, a Melachah for a non-constructive purpose, which is Tzerichah l'Gufah? Since it is a Melachah she'Einah Tzerichah l'Gufah, one should be exempt according to Rebbi Shimon even for Mekalkel b'Chaburah! (TOSFOS to Sanhedrin 84b, DH Man Shemat)
(a) According to Rashi, Rebbi Shimon maintains that one is Chayav only in a situation in which a person intends to do damage (such as by burning or hurting his friend; see Rashi DH Chutz and DH u'Mav'ir). Even though he intends to do damage, the damage is still objectively called "Mekalkel," and therefore Rebbi Yehudah exempts him for such an act, while Rebbi Shimon maintains that he is Chayav. (See MAHARSHA for another explanation. However, it does not seem from Rashi (DH u'Beraisa) that he would consider the Maharsha's case one of "Mekalkel.")
(b) TOSFOS (DH Chutz) disagrees with Rashi's analysis of Rebbi Shimon's opinion. According to Tosfos, the category of Melachah she'Tzerichah l'Gufah is much broader. Cooking on a wood fire is considered to be a Melachah she'Tzerichah l'Gufah even according to Rebbi Shimon. (That is, the category of Tzerichah l'Gufah includes not only a case in which the destruction of the wood is the objective, but even when the cooking of the food is the objective, and not the destruction of the wood.) Consequently, according to Rebbi Avahu, a situation of Mekalkel that is Tzerichah l'Gufah exists when a person lights a fire to cook food (which is Tzerichah l'Gufah) with wood that is, unbeknownst to him, Asur b'Hana'ah and therefore may not be used to cook in truth (and thus the act is Mekalkel).
Tosfos adds that Rebbi Yochanan, who says that an act of Chovel must be done for a constructive purpose such as to feed one's dog, also expresses the opinion of Rebbi Shimon, and not Rebbi Yehudah. According to Rebbi Yochanan, Rebbi Shimon maintains that one who does an act of Mekalkel of Chovel or Mav'ir is Chayav only when there is some degree of constructive outcome from the action, even though the action is not normally done for such a purpose (such as bruising in order to feed blood to dogs), or even though the constructive goal is attained only after the bruising has been done (the blood is fed to dogs only after the animal is bruised; Rabeinu Tam). Tosfos maintains that such an act is also considered to be Tzerichah l'Gufah, since the blood (i.e., the Neshamah that was removed) itself is used to feed the dogs. Rebbi Yehudah, who argues with Rebbi Shimon, requires fully constructive intent and thus maintains that one is not Chayav in the two cases mentioned above.
(According to Tosfos, Rebbi Shimon's only source that one is Chayav for an act of Mekalkel of Chovel or Mavi'r is a Gezeiras ha'Kasuv (it is learned from Milah on Shabbos, etc.), as the Gemara here concludes.)
2) "TZIPOR DROR"
QUESTION: Rabah bar bar Chanah says that the Mishnah (106a) discusses a "Tzipor Dror," a wild bird which does not accept authority. Such a bird is not considered captured even when it is enclosed in a house. RASHI (DH b'Tzipor Dror) explains that the reason the bird is not considered captured while it is in the house is because it flies from one corner of the house to the other and one cannot catch it.
In the Mishnah, however, Rashi (DH ha'Tzad Tzipor) explains that the bird is not considered captured because it escapes through the windows. Why does Rashi change his explanation? (Rashi in Beitzah (24a) also changes his explanation from the Havah Amina, in which he explains that the bird escapes through the windows, to the conclusion, in which he explains that the bird escapes by fleeing from one corner of the house to another.)
ANSWER: The Gemara initially suggests that the difference between a bird that is considered captured and one that is not considered captured depends on the type of enclosure surrounding the bird. If it is roofed, the bird is considered captured. If it is not roofed, the bird is not considered captured. If the Gemara at this stage means that the bird can evade capture by fleeing from one corner to the other, then it should not matter whether the enclosure is roofed or not; the bird can always escape. It must be that the Gemara at this stage refers to an ordinary bird that can escape only through open parts of the house (and not by fleeing from corner to corner).
The Gemara concludes that a bird is not considered captured even in a roofed area when that bird is a Tzipor Dror. Accordingly, it must be that the bird escapes by flying from corner to corner, and not by flying away through the windows. This is why a Tzipor Dror is the only bird that is not considered captured in such a situation.