1) "SHELISHI" FOR TERUMAH AND "REVI'I" FOR KODESH: MID'ORAISA OR MID'RABANAN
OPINIONS: The Gemara derives the Halachah of Shelishi l'Tum'ah for Terumah from a verse, and the Halachah of Revi'i l'Tum'ah for Kodesh from either a Kal v'Chomer or a Mah ha'Tzad. These sources imply that the respective degrees of Tum'ah for Terumah and for Kodesh are mid'Oraisa. Is this in fact the Halachah?
(a) RASHI in Sotah (29b-30a) implies that the Halachos of Shelishi for Terumah and Revi'i for Kodesh are both mid'Oraisa, and that the Kal v'Chomer of the Gemara is a full-fledged Kal v'Chomer. Although the Kal v'Chomer which the Gemara suggests can be refuted by the argument of "Dayo," nevertheless the Gemara there maintains that when a Kal v'Chomer will be rendered useless when the rule of "Dayo" is applied, we do not apply "Dayo" and the Kal v'Chomer remains in effect (as Rashi writes there, and in his first explanation here, DH Eino Din).
This is also the opinion of TOSFOS in many places (Pesachim 19a, DH Lo; Chulin 35a, DH Ein Lecha; Chagigah 21b, DH Basraisa #2).
(b) However, RASHI here (end of DH Eino Din) and in Pesachim (19a, DH Amar Lei) asserts that the law of Revi'i for Kodesh is only mid'Rabanan. Rashi in Pesachim proves this from the fact that Rebbi Yosi -- who teaches the Kal v'Chomer -- maintains that a solid food is Mekabel Tum'ah from neither a liquid nor a solid food, but only from a Kli (vessel). Since a Kli can never be less than a Rishon l'Tum'ah, the food which touches the Kli becomes a Sheni, and the liquid which touches the food becomes a Shelishi, after which nothing else becomes Tamei, mid'Oraisa. Rebbi Yosi here must be discussing the Tum'ah d'Rabanan of food or drink which touches another food, and thus the point of his Kal v'Chomer is to teach a Halachah d'Rabanan (i.e. the situation in which something can become Tamei with Revi'i l'Tum'ah).
Rashi here and in Pesachim cites further proof from the Gemara (21b) which states that the Chumra of Kodesh (that a Revi'i makes Kodesh become Pasul while only a Shelishi makes Terumah become Pasul) is only a "Ma'aleh d'Rabanan" which has no source in the Torah. (Tosfos in Pesachim cites a different Girsa of the Gemara here. Tosfos also attempts to reconcile the Gemara here with his opinion that Revi'i for Kodesh is mid'Oraisa, even according to Rashi's Girsa. See also Tosfos here, DH Minayin.)
(c) RASHI in Chulin (35a) seems to have a third opinion. Rashi explains that even the law of Shelishi for Terumah is only mid'Rabanan. According to Rashi, the Kal v'Chomer here is not a true Kal v'Chomer (perhaps because of the problem of "Dayo"), and it teaches only a Halachah mid'Rabanan.
This is also the opinion expressed by Rashi later in Chulin (128a, DH Mehader; see Gilyon ha'Shas and Rashash there), and it may also be the opinion of Rashi's second explanation here (DH Eino Din). (See Insights to Sotah 30:1
2) FOODS OF KODESH HANDLED IN A VESSEL WHICH IS NOT "MEKABEL TUM'AH"
QUESTION: The Gemara explains the Mishnah's (20b) tenth stringency of Kodesh over Terumah. One may eat dry foods of Chulin with hands that are Tamei with Sheni l'Tum'ah at the same time he has Terumah in his mouth. There is no concern that he will touch the Terumah with his Tamei hands as he places the Chulin into his mouth. In contrast, one may not eat Chulin with Tamei hands when he has Kodesh in his mouth. The Chachamim were stringent with regard to protecting the Taharah of Kodesh.
The Gemara explains how it is possible that one's mouth can be filled with food of Kodesh which is Tahor when his hands are Tamei. The Kodesh food should have become Tamei as soon as he picked it up with his hands to place it in his mouth. The Gemara answers in the name of the Tosefta (see Tosfos DH Lo) that either someone else (whose hands were Tahor) placed the Kodesh into his mouth, or he placed it into his mouth himself by holding it with a "Kush" or "Karkar," instruments which cannot become Tamei (such as a flat, wooden reed), as RASHI (DH O she'Tachvan) and TOSFOS (DH Lo Tzericha) explain.
Why does the Tosefta explain that he placed the Kodesh into his mouth specifically with utensils which cannot become Tamei? Even if he used utensils which can become Tamei, they would not render the Kodesh Tamei. The person's hands have the status of a Sheni l'Tum'ah; when they touch the utensil, they cannot make it Tamei because neither a Rishon nor a Sheni can make a utensil Tamei. Only an Av ha'Tum'ah can make a utensil Tamei. Accordingly, even if the utensil is one that can become Tamei, one is permitted to use it to place the Kodesh into his mouth because the utensil and the Kodesh that it holds remain Tahor. (TOSFOS YOM TOV)
(a) RAV YAKOV EMDEN (in LECHEM SHAMAYIM) answers that although a utensil normally cannot become Tamei through contact with a Rishon or Sheni l'Tum'ah, this general rule does not apply to a utensil used for Terumah or Kodesh. The Chachamim decreed that a utensil used for Terumah or Kodesh does become Tamei through contact with a Rishon or Sheni l'Tum'ah. Accordingly, when the person touches the utensil with his Tamei hands, his hands make the utensil Tamei which in turn makes the Kodesh Tamei. (Rav Yakov Emden bases this explanation on the Gemara in Berachos 52b.)
However, other Acharonim prove from a number of Mishnayos that there is no such decree; even when used for Kodesh, a utensil cannot become Tamei through contact with one's hands. (See NETZIV.)
(b) RAV YAKOV EMDEN suggests further that the Beraisa means that when a person's hands (or entire body) are Tamei, he should store his Terumah and Kodesh in utensils which cannot become Tamei. Placing the Terumah and Kodesh in such utensils serves as a reminder that he must not touch the Terumah and Kodesh with his hands.
Rav Yakov Emden cites an example of such a decree from the Gemara in Gitin (62a) which says that when a Chaver separates Chalah from the dough of an Am ha'Aretz on behalf of the Am ha'Aretz, he should place the Chalah into a flat wooden utensil which cannot become Tamei. This act will remind the Am ha'Aretz not to touch the Chalah, lest he make it Tamei before he gives it to a Kohen.
The RASHASH finds a more explicit source for this type of decree in the Mishnah in Tevul Yom (4:2). The Mishnah states that when a person who is a Tevul Yom (who has the status of a Sheni l'Tum'ah) wants to separate Chalah, he should place the dough on a flat wooden utensil which cannot become Tamei before he declares it to be Chalah. (The declaration of the dough as Chalah gives it the status of Terumah and enables it to become Tamei with Shelishi l'Tum'ah.) The BARTENURA and Rishonim there explain that the act of placing the dough on a flat wooden utensil reminds the person not to touch it, lest he make the Chalah Tamei.
(The comparison to the case of Chalah of a Tevul Yom is questionable. In the case of a Tevul Yom, the person originally separated the Chalah from the dough himself while it was still Chulin. Since he began to handle it himself, he needs a reminder not to continue to handle it after he declares it Chalah. In contrast, in the case of the Gemara here, there is no reason to suspect that a person with Tamei hands will touch the Kodesh himself.)
(c) The OR HA'CHAIM (in RISHON L'TZIYON) explains that the Tosefta recommends that one use a utensil (such as a Kush or Karkar) which cannot become Tamei just in case a drop of liquid wets the utensil where one's hands are touching it. Liquids that become Tamei from hands (which are Tamei with Sheni l'Tum'ah) can make a utensil Tamei (Tosfos to Shabbos 14b, DH Ela), which in turn can make the Kodesh Tamei. Therefore, the Tosefta states that he placed the Kodesh into his mouth specifically with utensils which cannot become Tamei.
3) A "REVI'IS" OF OIL OF KODESH
QUESTION: The Mishnah states that after the wine-pressing and olive-pressing seasons have passed, an Am ha'Aretz is not trusted to say that his Terumah is Tahor. If he brings wine of Terumah to the Kohen after the end of the wine-pressing season, the Kohen may not accept it from him. However, if the Am ha'Aretz says that he separated a Revi'is of Kodesh into the barrel of wine, he is trusted and the Kohen may accept the entire barrel from him.
RASHI writes that when the Mishnah says a "Revi'is of Kodesh," it means a "Revi'is of a Log of oil."
Why does Rashi write that the Revi'is mentioned in the Mishnah is a Revi'is of oil? The previous case in the Mishnah discusses a barrel of wine of an Am ha'Aretz. This part of the Mishnah seems to be a continuation of that case. Rashi should explain, as the BARTENURA and others do, that the Am ha'Aretz separated a Revi'is of wine of Kodesh into the barrel.
ANSWER: RAV YOSEF BEN-ARZA (in YOSEF DA'AS) quotes IYUNIM B'DIVREI CHAZAL by RAV CHANOCH EHRENTROY who gives the following answer. TOSFOS in Chulin (35b, DH v'Im) asks why the Kohen is permitted to eat the contents of the barrel which the Am ha'Aretz brings to him. Although the Am ha'Aretz is believed to say that he guarded the barrel from Tum'ah because of the Kodesh that is inside of it, the Kohen may not eat the Terumah in the barrel if it is mixed with Kodesh (since Kodesh is forbidden)!
Tosfos in Zevachim (88a, Min ha'Meduma) answers that the Am ha'Aretz does not actually separate Kodesh into the barrel. Rather, he plans to separate some of the wine in the barrel and consecrate it, and that is why he guards it from Tum'ah.
However, this answer is not feasible according to Tosfos later (25b, DH bi'Metaher). Tosfos there proves from the Mishnah that an Am ha'Aretz is trusted to guard Kodesh through the entire year only if he actually separated the Kodesh. If he just planned to consecrate some of the wine as Kodesh at a later time, he is trusted only for seventy days before the time of wine-pressing. (See TIFERES YISRAEL (Boaz), who raises this point and attempts to find another answer to the question of Tosfos in Chulin.)
Rashi answers this question when he explains that the Revi'is of Kodesh which the Am ha'Aretz placed into the barrel is a Revi'is of a Log of oil. Since wine and oil do not mix together, the Kohen is able to separate the oil in the barrel from the wine, drink the wine, and use the oil for purposes of Kodesh!