ARE SHABBOS AND YOM TOV ONE KEDUSHAH?
(Mishnah - R. Eliezer): If Yom Tov is right before or after Shabbos, one can stipulate to make one Eruv for the first day in the east, and for the second day in the west, or vice-versa;
He can be Me'arev just for the first day, and the second day he is like residents of his city [without an Eruv], or vice-versa;
Chachamim say, he is Me'arev in one direction, or not at all. He is Me'arev for both days, or not at all;
How can one Me'arev [for both days without risking that the Eruv will get lost?] He takes the Eruv [to the desired place of Shevisah] on Erev Yom Tov, remains there until nightfall, and then takes it home with him. (If our Mishnah is like the Halachah, that anyone can be Me'arev without food through being at the desired place of Shevisah at nightfall, it must discuss a Shali'ach);
The next day he takes it back, and remains there until nightfall. He may eat it and return. He earns permission to walk [further in that direction], and also gets to eat his Eruv.
If the Eruv was eaten on the first day, it is valid only for the first day.
R. Eliezer: This shows that you admit to me that the Kedushah of each day is separate! (Therefore you should also permit a different Eruv for each day.)
(Gemara) Question: [Chachamim say that he is Me'arev] in one direction. This means for both days;
[They also say that he is Me'arev] for both days. This means in one direction. Why do they repeat themselves?
Answer: They say to R. Eliezer 'don't you agree that one may not be Me'arev for half the day to the north and half the day to the south?!'
R. Eliezer: I agree.
Chachamim: Similarly, one cannot do so on consecutive days!
R. Eliezer: One can do so on consecutive days, for each is a separate Kedushah! Don't you agree that if one was Me'arev through walking on the first day, he needs to be Me'arev through walking on the second day! Don't you agree that if the Eruv was eaten on the first day, he may not rely on it on the second day!
Chachamim: We agree.
R. Eliezer: You agree that they are two [separate] Kedushos!
Chachamim are unsure whether or not they are two Kedushos, therefore they are stringent to be concerned for both possibilities.
Chachamim: Don't you agree that one may not begin to be Me'arev on Yom Tov for Shabbos (i.e. if he was not Me'arev for Yom Tov)? This shows that they are one Kedushah!
R. Eliezer: No, it is because one may not prepare for Shabbos on Yom Tov.
(Beraisa - Rebbi): If one was Me'arev through walking on the first day, he must be Me'arev through walking on the second. If his Eruv was eaten on the first day, he may not rely on it on the second;
R. Yehudah says, he is in [a status of] Chamar Gamal;
R. Shimon ben Gamliel and R. Yishmael the son of R. Yochanan ben Brokah say, if he was Me'arev through walking on the first day, he need not be Me'arev through walking on the second. If his Eruv was eaten on the first day, he may rely on it on the second.
(Rav): The Halachah follows the following four Tana'im according to R. Eliezer, who says that they are two Kedushos -- R. Shimon [ben Gamliel], R. Yishmael [son of R. Yochanan ben Brokah], R. Elazar b'Rebbi Shimon, and R. Yosi b'Rebbi Yehudah Stimta'ah (he is the author of many Stam Mishnayos);
Some include R. Elazar among the four and exclude R. Yosi b'Rebbi Yehudah.
Objection: R. Shimon and R. Yishmael hold that they are one Kedushah!
Answer: We must switch their opinion in the Beraisa. (They do not permit the second day due to the Eruv of the first day, unless he again walks there or if the food is still there.)
Question: If so, they do not argue with Rebbi!
Answer: Indeed, it should say 'also R. Shimon and R. Yishmael say...'
Question: Rav should include Rebbi, and say that the Halachah follows five Tana'im according to R. Eliezer!
Answer: Rebbi taught the opinion of R. Eliezer, but he does not hold like it.
Question: [Perhaps] also R. Shimon and R. Yishmael taught R. Eliezer's opinion, but do not hold like it!
Answer: Rav had a tradition [that these four Tana'im hold like R. Eliezer].
YOM TOV MAY NOT PREPARE FOR SHABBOS
After Rav Huna died, Rav Chisda posed a contradiction in Rav's teachings;
Rav taught that the Halachah follows the four Tana'im according to R. Eliezer, who says that they are two Kedushos;
(Rav): [If Yom Tov is right before or after Shabbos] if an egg was laid on the first day, it is forbidden on the second.
Answer (Rabah): That is [not because they are one Kedushah, rather,] due to Hachanah:
"V'Hayah ba'Yom ha'Shishi v'Hechinu" - a weekday can prepare for Shabbos or Yom Tov, but Yom Tov cannot prepare for Shabbos or vice-versa.
Question (Abaye - Mishnah): How can one Me'arev [for both days]? He takes the Eruv on Erev Yom Tov, remains there until nightfall, and then takes it home with him. The next day he takes it back and remains there until nightfall; at which point he may eat it and return.
This is preparing for Shabbos on Yom Tov!
Answer (Rabah): Do you think that an Eruv acquires at the end of the [previous] day?! You are wrong! Rather, it acquires at the beginning of the [coming] day, Shabbos prepares for itself.
Question: If so, one should be able to be Me'arev in a Kli [that is a Tevul Yom with Ma'aser Tevel, and to stipulate that it become Terumas Ma'aser at dark. A Mishnah (cited above, 36a) disqualifies this!]
Answer: The Eruv is invalid because it was forbidden to eat it before Shabbos.
Question (Mishnah - R. Eliezer): If Yom Tov is right before or after Shabbos, one can be Me'arev [for the first day in the east, and for the second day in the west];
[The Eruv for the second day is valid, even though] he cannot eat it during the [first] day [for the first Eruv forbids him to go to the west]!
Answer: You assume that both Eruvin are 2000 Amos [from the city]. This is wrong. Rather, each Eruv is 1000 Amos away. (The first Eruv forbids him only to go more than 1000 Amos west of the city.)
Question (Abaye): Rav Yehudah taught that if one was Me'arev through walking on the first day, he may be Me'arev through walking on the second day. If he was Me'arev with bread on the first day, he may be Me'arev with bread on the second day;
Yom Tov prepares for Shabbos!
Answer (Rabah): You assume that he goes and says that he is Me'arev for the second day. This is wrong. Rather, he goes and is silent.
Suggestion (Abaye): This is like R. Yochanan ben Nuri, who says that Hefker objects acquire Shevisah (no acquisition is needed)!
Rejection (Rabah): It is even like Chachamim. They argue about one who was sleeping, for he could not have spoken;
They agree about one who was awake. Since he could speak, even if he did not speak, it is as if he spoke!