QUESTION: Zeiri and Rav argue whether "Eshes Avi Imo" -- the wife of the
father of one's mother -- has a "Hefsek" or not; is that relation prohibited
for only that generation (the wife of the father of one's mother), or is
that relation prohibited for preceding generations as well (such as the wife
of the father of one's grandmother)? Zeiri maintains that "Eshes Avi Imo" is
not prohibited in any other generation. Rav maintains that the prohibition
does extend to earlier generations.
Rav explains that even though there is no Ervah d'Oraisa involved in the
first generation (since his mother cannot be married to a wife),
nevertheless the Chachamim decreed that "Eshes Avi Imo" is prohibited for
all prior generations because of the existing prohibition of "Eshes Avi
*Aviv*," the wife of the father of one's *father*, which does have an Ervah
d'Oraisa in the first generation ("Eshes Aviv," the wife of one's father).
Since the wife of his mother's father and the wife of his father's father
are easily confused, the Chachamim gave them the same Halachah and
prohibited both.
Zeiri argues and says that they are not easily confused. A person spends
much more time with his father's family than with his mother's family, and
thus he will not easily confuse the two.
According to Zeiri, who asserts that one does not confuse the relatives on
his maternal side with those on his paternal side, why is it that the
Chachamim prohibited one's father's mother (his paternal grandmother)
without "Hefsek," for all earlier generations? RASHI (DH v'Eshes Achi ha'Av)
explains that the father's mother does not have an Isur in the first
generation (because there is no woman with that relation to him in the first
generation), and nevertheless this relation is Asur for all generations
because she is confused with the grandmother on the maternal side, one's
mother's mother. Everyone, including Zeiri, agrees with this! Why, then, is
Zeiri not concerned that we will confuse the maternal and paternal sides in
the case of "Eshes Avi Imo," the wife of one's mother's father's?
ANSWER: RASHI (DH Hasam) alludes to the answer to this question when he says
that because a person spends much more time with his father's family, he
considers the relatives on that side to be "more closely" related than those
on the maternal side. Thus, there is more reason to prohibit a relative on
one's paternal side.
Consequently, Zeiri says that the Chachamim did not prohibit the maternal
side just because the paternal side is Asur, and therefore the wife of one's
mother's father is not Asur. The Gemara earlier was discussing the opposite
situation -- prohibiting the paternal side because the maternal side is
Asur. If one's mother's mother is Asur, then the Chachamim should also
prohibit one's father's mother, because the paternal side is always treated
more stringently due to the higher degree of closeness that one feels with
the relatives on the paternal side.
According to Rashi, that is what the Gemara is saying -- the fact that one
spends more time with them is more reason to make them Asur. This actually
supports the words of the RAMBAM and IBN EZRA (quoted by the RAMBAN in
Vayikra 18:6) that the reason for the Isur of Arayos is to prohibit marrying
the women whom one associates with most often, the women whom he has
interactions with most commonly, in order to prevent a person from acting
like an animal, which mates with all of the females that are around him. (M.
Kornfeld)