1) "YAD L'TUMAH"
OPINIONS: The Gemara quotes the Mishnah in Uktzin (1:1) that states that a Yad (a handle for a food or utensil) which is not a Shomer (it does not protect or preserve the food or utensil) brings Tum'ah to the food if Tum'ah touches the Yad, and it transfers Tum'ah from the food to other food, but it does not combine with the food for the minimum amount needed to be Mekabel Tum'ah.
The Mishnah says that a Yad transfers Tum'ah, but it does not mention whether the Yad itself becomes Tamei. Does the Yad itself become Tamei?
(a) The RAMBAM (Perush ha'Mishnayos to Uktzin 1:1) explains that a Yad does become Tamei, since it is considered part of the food.
HAGA'ON RAV YISRAEL ZEV GUSTMAN zt'l (in Kuntresei Shi'urim, Bava Kama 9) quotes the words of RASHI here (in both DH Tamei) who clearly learns that the Yad itself becomes Tamei. This view is also expressed by Rashi later (123a, DH Tefach).
The Acharonim point out that even according to the Rambam and Rashi who say that the Yad itself becomes Tamei, it remains Tamei only while it is attached to the food, but not when it becomes detached.
(b) The CHAZON YECHEZKEL (Likutim 241-242) and HAGA'ON RAV YISRAEL ZEV GUSTMAN zt'l (loc. cit.) quote TOSFOS later (128a, DH Behemah) who writes, "All Yados are not Mekabel Tum'ah; rather, they serve merely as a conduit to bring in and pass on Tum'ah."
According to Tosfos, it is easy to understand why the Gemara asks that perhaps a Yad serves only to "pass on" Tum'ah, but not to "bring in" Tum'ah. If a Yad is considered part of the food, as the Rambam says, and that is why it serves as a conduit for Tum'ah, then there should be no difference between passing on Tum'ah and bringing in Tum'ah. (Z. Wainstein)
2) BECOMING "TAMEI" WHILE ATTACHED TO THE GROUND
QUESTION: Rebbi Yochanan maintains that just as a Yad transfers Tum'ah to the food to which it is attached, it is also able to cause the food to become Huchshar for Tum'ah. The Gemara quotes a Beraisa that supports Rebbi Yochanan's view. The Beraisa says that "just as a Yad can transfer Tum'ah, a Yad can also bring Hechsher." The Beraisa adds that "just as they (fruits) are not Mekabel Tum'ah until they are uprooted, they do not become Huchshar for Tum'ah until they are uprooted."
RASHI (DH uch'Shem) quotes the Toras Kohanim that says that produce is not Mekabel Tum'ah while it is attached to the ground, because if it would be Mekabel Tum'ah in that state, all produce would be Tamei as a result of contact with Sheratzim.
According to the logic of the Toras Kohanim, why does the Beraisa compare Hechsher to Tum'ah, saying that "just as they are not Mekabel Tum'ah until they are uprooted, they do not become Huchshar for Tum'ah until they are uprooted"? The Beraisa implies that we know first that Kabalas Tum'ah occurs only after the produced is detached from the ground, and from there we learn that Hechsher also occurs only after the produce is detached. However, the logic of the Toras Kohanim seems to apply to Hechsher as well: produce cannot become Huchshar for Tum'ah while attached to the ground because, otherwise, everything should become Huchshar from the rain that falls on it. There should be no need to compare Hechsher to Kabalas Tum'ah in order to know that it does not apply to produce that is attached to the ground! Moreover, since produce cannot become Huchshar while attached to the ground, it obviously cannot become Tamei either. Why, then, does the Toras Kohanim explain this logic only with regard to Kabalas Tum'ah and not with regard to Hechsher Tum'ah?
(a) Perhaps the Toras Kohanim means that even if the food would be able to become Huchshar due to the rain while attached to the ground, it still would not be able to become Tamei until it is detached.
who answers that the fact that it rained does not automatically make the produce Huchshar for Tum'ah, because perhaps the owner of the field was not pleased that it rained at the time (for example, he was traveling). The owner must be pleased that his produce became wet in order for it to be Huchshar for Tum'ah. (See Insights to Chulin 31:3
(c) The Rashba quotes the RAMBAN who explains that the Beraisa indeed could have learned from Hechsher that Kabalas Tum'ah does not apply to produce attached to the ground. The reason why the Beraisa instead writes that we learn from Kabalas Tum'ah that Hechsher does not apply is merely in order to maintain consistency with the preceding statement of the Beraisa, which learns Hechsher of Yad from Kabalas Tum'ah of Yad. (Z. Wainstein)
3) COMBINING FOOD TO FORM A "SHI'UR TUM'AH"
QUESTION: Rav says that the laws of Yad do not apply to a Yad attached to a food that is less than a k'Zayis in size.
Rav seems to be saying that the laws of Tum'as Ochlin apply only to a food that is at least a k'Zayis. However, the Rishonim disagree about the size that a food must be in order to be Mekabel Tum'ah. RASHI in Pesachim (33b, DH b'k'Beitzah) quotes the Toras Kohanim which implies that even the smallest piece of food is Mekabel Tum'ah mid'Oraisa. However, in order to cause something else to become Tamei, the food must be at least a k'Beitzah, as Rashi in Chulin (25a, DH v'Afilu; see Insights there) and elsewhere writes.
TOSFOS in Pesachim (33b, DH l'Eimas) maintains that the Toras Kohanim is teaching only an Asmachta for a Halachah d'Rabanan. A piece of food smaller than a k'Beitzah is Mekabel Tum'ah only mid'Rabanan. Mid'Oraisa, the food must be at least a k'Beitzah in order to become Tamei. The RASHBA maintains that food which is less than a k'Beitzah is not Mekabel Tum'ah at all, even mid'Rabanan.
How do these Rishonim understand the statement of Rav, who implies that the food becomes Tamei when it is a k'Zayis?
(a) RASHI (DH Ein Yad l'Pachos) explains that Rav is referring to a Yad that is attached to a piece of food less than a k'Zayis (such as a bean), and that food is together with other food which comprises at least a k'Beitzah. Rav says that if Tum'ah touches the Yad, the food does not become Tamei.
TOSFOS (DH Ein Yad) questions Rashi's explanation. When the food attached to the Yad is less then a k'Zayis, it does not become Tamei even when the Tum'ah touches it directly (bypassing the Yad), and even when it is together with other food that is at least a k'Beitzah. One of his proofs is the Gemara earlier (24b) which derives from a verse regarding a Kli Cheres (an earthenware vessel) that is Tamei (and thus is Metamei any food that enters its airspace) that even when the Kli Cheres is filled with mustard seeds (each of which are much smaller than a k'Zayis), they are all Tamei. Tosfos points out that according to Rashi, there is no need for the Gemara to derive this from a special verse; the normal law of Tum'as Ochlin teaches that small amounts of food that are merely touching each other are always considered connected. The fact that a verse is necessary in that case shows that, in general, small, unconnected pieces of food do not join to make a Shi'ur when they are merely touching.
(b) TOSFOS explains that Rav is discussing a case in which the piece of food that is less then a k'Zayis is attached weakly to a larger piece of food. If one picks up the food by the Yad, only the piece that is less than a k'Zayis will be lifted up; the Yad does not support the rest of the food.
If the food itself that is less than a k'Zayis is touched by Tum'ah, then the entire k'Beitzah becomes Tamei, because this piece of food is connected to the food that is the size of a k'Beitzah. Similarly, if the food is the size of a k'Zayis and its Yad is touched by Tum'ah, the Yad conveys the Tum'ah to the k'Beitzah, because the Yad is considered a significant Yad since it is attached to a k'Zayis. However, when the Yad is attached to a piece of food that is less than a k'Zayis, it is not a significant Yad at all and it does not convey Tum'ah. This is what Rav is teaching.
The KEHILOS YAKOV (#34) writes that the proof of Tosfos -- that foods that are touching each other but are not connected do not combine to make a Shi'ur of Tum'ah -- applies only in a case in which the object making them Tamei is touching only part of the food. If the object is touching all of the food simultaneously, then Tosfos has no proof that pieces of food that are touching each other, but are not connected, cannot combine to become Tamei.
It seems that Tosfos could have explained that Rav's case involves two foods that are only touching, and the Tamei object touches both of them simultaneously. From the fact that Tosfos explains the case to be one in which the foods are somewhat connected, it is apparent that Tosfos maintains that even when the Tamei object touches food items that are touching each other, it does not make the food Tamei.
The MISHNEH L'MELECH (Hilchos Tum'as Ochlin 4:3) also writes that Tosfos and the RASHBA require that separate food items be connected in order to combine to make the minimum amount necessary to become Tamei. The Kehilos Yakov concludes that it must be that Tosfos and the Rashba either have some source that a connection is required, or they maintain that the simultaneous contact between a Tamei object and all of the foods that are touching each other does not provide any logical reason for them to combine to form the minimum amount of the Shi'ur of Tum'ah.
The Mishneh l'Melech adds that this may be the basis of the dispute between Rashi and Tosfos here. Rashi maintains that a k'Beitzah of food can be comprised of many pieces touching each other, while Tosfos and the Rashba maintain that the pieces of food must be connected in order to combine to make a k'Beitzah. The Mishneh l'Melech sides with Tosfos and asserts that this is also the opinion of the RAMBAM.
However, the Gemara later (124b) seems to contradict the logic of Tosfos. Rebbi Akiva there says that one can become Tamei from touching two different pieces of Neveilah, each of which is only half of a k'Zayis. (The minimum amount of Neveilah that is Metamei is one k'Zayis.) Other, similar opinions are found throughout the Gemara (see, for example, Ohalos 3:3). This implies that if foods that merely touch each other are simultaneously touched by a source of Tum'ah, then they should become Tamei, even though each food by itself is less than the Shi'ur of Tum'ah.
Tosfos in Nazir (50b, DH Ta Shema Chelev) differentiates between the law of combining Tamei items in order to make a third object Tamei, and combining food so that it should become Tamei itself. He states that Tamei items combine (even when they are merely touching and are not connected) only to make things that they touch become Tamei. In order to become Tamei themselves, foods do not combine when they are not connected. (See Kehilos Yakov #34, DH v'Nir'eh, for the logic behind this difference.) (Y. MONTROSE)