QUESTION: The Mishnah states that Nezirus takes effect on Nezirus, but a
Shevu'ah does not take effect on a Shevu'ah. The Gemara cites Rav Huna who
explains that this means that a person who makes, at one time, two oaths to
become a Nazir on two consecutive days must observe thirty days of Nezirus
for his first oath, and when he finishes the first Nezirus, he must observe
another thirty day Nezirus for the second oath. In contrast, when one makes
two Shevu'os, first making a Shevu'ah that he will not eat figs, and then
making a Shevu'ah that he will not eat both figs and dates together, the
second Shevu'ah does not take effect since he is already prohibited from
eating figs (by the first Shevu'ah).
Why should the Halachah of Nezirus differ from the Halachah of Shevu'os? If a
Shevu'ah cannot take effect on a pre-existing Shevu'ah because the person is
already prohibited from part of the items in his Shevu'ah due to the first
Shevu'ah, then so, too, one's acceptance of a second Nezirus should not take
effect because the first twenty-nine days of that Nezirus are already
included in the first Nezirus! Even though the Gemara (18a) cites a verse,
"Nazir l'Hazir" (Bamidbar 6:2), that teaches that Nezirus takes effect on
Nezirus, and thus there is a Gezeiras ha'Kasuv for Nezirus, we should still
learn from that Gezeiras ha'Kasuv that a Shevu'ah takes effect on a Shevu'ah!
This is because, as we learned (3a), the Halachos of Nedarim can be learned
from Nezirus through a Hekesh, and the RAN (beginning of 7a) explains that
all of the Halachos that are learned from Nezirus to Nedarim apply also to
Shevu'os because of a Hekesh between Nedarim and Shevu'os (it is this Hekesh
which teaches that Yados work for Shevu'os). Therefore, we should learn from
the verse of "Nazir l'Hazir" that a Shevu'ah, too, takes effect on a
Shevu'ah!
ANSWER: There is a logical reason why a Shevu'ah should not take effect on
another Shevu'ah when the second Shevu'ah includes objects already prohibited
by the first Shevu'ah. Since the second Shevu'ah does not take effect on the
objects that are already prohibited, but can only take effect on the other
objects, then if the Shevu'ah were to take effect it would not be taking
effect in the manner in which the person desired! Perhaps the person did not
want to make a Shevu'ah only on part of the objects he mentioned, but he
wanted to make a Shevu'ah that included all of the objects. Since he might
not have wanted to make a Shevu'ah on only part of the objects, the entire
Shevu'ah does not take effect. (This is related to the concept of "Neder
(Shevu'ah) she'Hutar Miktzaso, Hutar Kulo" (25b). Even though some Tana'im
maintain that a Neder (or Shevu'ah) that was partially annulled does *not*
become completely annulled, that is only when the person mistakenly included
something in his Neder that he himself did have any intention to include in
the Neder. Since he did not want it to be part of the Neder, when that part
of the Neder is annulled it does not affect the rest of the Neder. But when
he *wants* to include two things in his Neder but the *Torah* does not let
him make both of them Asur, then everyone agrees that we apply the principle
"Neder she'Hutar Miktzaso Hutar Kulo.")
The Torah tells us that Nezirus is different, and the second Nezirus that he
made, accepting upon himself to observe a second Nezirus the following day,
does take effect. However, there is a very strong logical argument to
differentiate between Nezirus and Shevu'os. The reason a second Nezirus takes
effect is that although the first twenty-nine days cannot take effect because
he is already Asur (to drink wine, cut hair, etc.) due to the first Nezirus,
the *thirtieth* day of the second Nezirus *can* take effect, since the first
Nezirus does not extend to that day. He will then have one day of Nezirus.
Once he has that one day of Nezirus to observe, he automatically must observe
a full thirty days, because of the rule that no Nezirus can take effect for
less than thirty days (Nazir 7a). Therefore, that day automatically expands
to become a thirty-day Nezirus. Hence, even if the person intended for the
second Nezirus to be observed for thirty days starting from the very next day
(so that twenty-nine of those days overlap with the first Nezirus), and he is
not getting what he wanted (but rather a one day Nezirus after the conclusion
of his first Nezirus), that one day Nezirus will expand into thirty days of
Nezirus, and thus he will be a Nazir anyway for thirty days as a result of
his second oath of Nezirus. That is why the Torah says that Nezirus takes
effect upon Nezirus. In the case of a Shevu'ah, though, if the first half of
the Shevu'ah does not take effect, then the Shevu'ah will never fit into the
words that he articulated. Therefore, Shevu'ah cannot be learned from Nazir.
Even a Hekesh will not teach us to learn Shevu'ah from Nazir when there is a
strong logical factor to distinguish between the two. (The principle of "Ein
Meshivin Al ha'Hekesh" means that we cannot disprove a Hekesh by finding a
Chumra or Kula in one of the two categories being compared to each other
(while a Chumra or Kula can be used to disprove a Kal v'Chomer or Binyan Av).
However, a stronger argument certainly can refute a Hekesh (see Insights to
Yevamos 3:2, in the name of SEFER KERISUS).