2a: https://dafyomi.co.il/nedarim/tosfos/nd-ts-017.htm
Ran 17a: v'Lo li'Mnos Shtayim Gam Kein d'Lo Mishkachas Lah Mah she'Ein Kein b'Nezirus
Why is it that a shvua never entails multiple undertakings from multiple upfront pronouncements? After all, it can be time-bound just like nzeirus.
Paul Davidowitz, United States
Very nice question. I see a few explanations in the commentaries for why the second Shevu'ah does not kick in, unlike Nezirus.
A) Tosfos: A Nezirus has a fixed timeframe of thirty days, unlike Neder/Shevu'ah. Therefore, we assume he means to add another period. In contrast, in Neder/Shevu'ah he is understood to mean specifically the same period of time, in which case it cannot take effect (1).
B) Ramban: The nature of Neder/Shevu'ah is that it can only apply to something that is not related to Cheftzei Shamayim.
C) Rebbi Akiva Eiger (on Shulchan Aruch and on the Mishnah): One Isur cannot apply on top of another one.
D) Avnei Milu'im (Siman 12): One oath cannot apply on top of another oath. Note: This is different from Rebbi Akiva Eiger, because according to Rebbi Akiva Eiger the second oath actually would take effect, just the person would not be punished, unlike the Avnei Miluim, according to whom the second oath does not take effect at all. Two practical differences emerge from this: First, when the person violates the second oath did he do a sin? According to Rebbi Akiva Eiger, yes. According to the Avnei Milu'im, no. Second, if the person would be released somehow from his first oath, does the second oath take effect? According to Rebbi Akiva Eiger, yes. According to the Avnei Miluim, no.
E) Chazon Ish (Even ha'Ezer #136, DH v'Elu Mutarin, #5): No Isur can apply on top of another Isur, not only in Neder/Shevu'ah but even in Nezirus. But in Nezirus, when the person makes his double declaration, he does not take on two Isurim per se. Rather, he takes on a double dose of Kedushah, which can take effect, and that translates to conducting two consecutive periods of Nezirus.
Best wishes,
Yishai Rasowsky
Thanks. Your term "Neder/Shevu'ah" regarding Neder excludes Nezirus (even though the latter is a type of the former) -- is that correct?
Kol Tuv,
-PD
Sure. Yes, even though Nezirus is a type of Neder, nevertheless it is excluded, as we see in the Mishnah which Davka chose to speak about Nezirus. And if I am not mistaken, the point you are analyzing is something that Tosfos (in A above) wanted to help address. He explains that unlike an ordinary Neder, a Nezirus has an inherent timeframe. The Chazon Ish (in E above) helps further to explain why it works, namely, because even though Ein Isur Chal Al Isur, but Kedushah can be Chal on Kedushah, which is where the sequential sets of Isurei Nezirus stem from.
Gmar Chasimah Tovah,
Yishai Rasowsky