QUESTION: Rav Yehudah in the name of Rav says that one who tears open a sewn collar (and thereby forms the hole in a shirt through which one puts his head) on Shabbos is Chayav to bring a Korban Chatas. RASHI says that the transgression is "Makah b'Patish," performing the final act to complete an object. The RITVA in Makos (3b) also explains that one is Chayav because of "Makah b'Patish." He adds that one is not Chayav for "Kore'a Al Menas Litfor," tearing for the sake of sewing, because he does not tear the collar with intention to sew an improved seam.

However, the Gemara later (105b) says that a person who tears his clothing on Shabbos to assuage his anger is Chayav for Kore'a. The Rishonim explain that even though he does not tear his clothing with intention to sew it again, his act is nevertheless considered a constructive one (it serves a constructive purpose of assuaging his anger) and therefore he is Chayav. According to the Gemara there, whenever tearing is done as a constructive act, one is Chayav for Kore'a. Why, then, is tearing open the collar of a shirt in order to make a hole for the neck not considered Kore'a?

(a) The BI'UR HALACHAH (OC 340) says that it is not considered Kore'a for another reason (and not because it is done for a purpose other than re-sewing). Kore'a refers to an inherently destructive act which is done to bring about a constructive result. In the case of tearing open the collar, the act if tearing is not destructive at all; it is completely constructive, for it is done in order to make a hole for the neck!

(b) The RAMBAM (Hilchos Shabbos 10:11) says that one indeed is Chayav for Kore'a in this case, because this is a Keri'ah with a constructive purpose.

QUESTION: The Beraisa says then when two parts of an instrument are attached to each other (such as a two-part scissors, or a carpenter's plane), they are considered attached ("Chibur") mid'Oraisa with regard to being Mekabel Tum'ah while they are being used.

If two, attached parts of an instrument are considered to be a single instrument with regard to Tum'ah, then why does the Gemara earlier say that the Beis ha'Pach of an oven, or two garments that were attached to each other by the launderer, are considered attached only mid'Rabanan, even b'She'as Melachah (i.e., while the oven is in use or while the clothes are being washed)?

ANSWER: TOSFOS (DH Iy Chibur) says that two items attached to each other are considered to be attached mid'Oraisa only when those two parts need each other in order to do their job. In the case of the Gemara earlier, each garment has its own separate use (and the two garments are attached only for the sake of laundering them). Similarly, the Beis ha'Pach has a separate use from the oven. Therefore, they are not considered attached mid'Oraisa.