QUESTION: The Gemara rounds out its list of the Sheniyos l'Arayos with the
Sheniyos of Rebbi Chiya. Rebbi Chiya adds six Sheniyos. The first four
Sheniyos of Rebbi Chiya include the daughter of the third generation through
one's son, the daughter of the third generation through one's daughter, the
daughter of the third generation through one's wife's son, and the daughter
of the third generation through one's wife's daughter.
RASHI (DH Shelishi and DH v'sh'Bibito) explains that these refer to the
daughter of the son of one's son, the daughter of the son of one's daughter,
the daughter of the son of one's wife's son, and the daughter of the son of
one's wife's daughter.
According to Rashi's explanation, why does Rebbi Chiya only discuss the
daughter of the *son* of one's son or daughter, and makes no mention of the
*daughter of the daughter* of one's son or daughter? Likewise, he mentions
only the daughter of the *son* of one's wife's son or daughter, but not the
*daughter of the daughter* of one's wife's son or daughter! He only mentions
cases where there is a woman at the end (obviously, since we are discussing
a prohibited woman) and at the beginning, but not when there is a woman in
the middle generation! Why does Rashi exclude such a case from Rebbi Chiya's
list of Sheniyos? (Indeed, the RAMBAM in Perush ha'Mishnayos and the
BARTENURA include those cases in their list of the Sheniyos of Rebbi Chiya!)
ANSWER: REBBI ELAZAR MOSHE HOROWITZ answers that later in the Gemara, the
Gemara questions whether the Sheniyos of Rebbi Chiya have "Hefsek" (and they
do not extend to further generations) or not (and they do extend to further
generations). In a case of the daughter of one's daughter's daughter, where
the first, second, and third generations are all women, then it is obvious
that the Isur continues down through the generations, because the first
generation is Asur mid'Oraisa (his daughter), and the second generation is
also Asur mid'Oraisa (his daughter's daughter), and whenever there is any
generation in which this relation is Asur mid'Oraisa, it is Asur throughout
all of the generations (as Rashi explained earlier, 21a DH v'Eshes -- see
Chart). Hence, if Rebbi Chiya was referring to the daughter of one's
daughter's daughter, the Gemara would not ask whether it has Hefsek or not.
The only question is in the case of the daughter of the *son* of one's
daughter. There, even though the first generation is mid'Oraisa (his
daughter), there is a son in the middle that stops the Isur, and there is no
case of an Ervah with a son in a middle generation, following a daughter,
which is Asur mid'Oraisa. That is why the Gemara asks whether the
prohibition of the daughter of the son of one's daughter continues for
ensuing generations or not.