Chapter 3, Mishnah 6. This Mishnah is divided into two parts. Its first part is structured exactly like the previous one, except that instead of his daughter and his wife's daughter, the Mishnah deals with his mother-in-law, his mother-in-law's mother, and his father-in-law's mother, three additional cases where the calculation is completely identical, except for the first of the seven prohibitions due to which that woman is forbidden to him, and for each and every one of them there is a penalty of kares and an independent obligation for a sin-offering. The study requires careful tracking, and therefore we will use the names appearing in the ArtScroll diagrams. The second part of the Mishnah deals with a completely different point.
The First Case - One Who Has Relations With His Mother-In-Law:
Reuven is the groom, and Basemas is the mother-in-law. The family tree: Yishmael has a daughter named Basemas; from Basemas, Yishmael had another daughter, Yehudis; and Yehudis married Reuven.
At this stage, Basemas is already forbidden to Reuven in two ways at once:
His mother-in-law - He is married to Yehudis, and Basemas is her mother. This is the primary prohibition.
His wife's sister - Yehudis and Basemas have one father, Yishmael. They are paternal sisters, and that is sufficient.
From here on, the additional prohibitions join in:
His daughter-in-law - Reuven has a son from another marriage, Chanoch, and he marries Basemas. The marriage dissolves, but she remains his daughter-in-law forever.
His brother's wife - Afterwards, Basemas marries Shimon, Reuven's brother, and even though this marriage dissolves, she remains his brother's wife or divorcee forever. There is no issue of yibbum here, and it does not help at all.
His father's brother's wife - For the third time, Basemas marries Esav, Reuven's father's brother, which is also an independent prohibition.
A married woman - Because she is still married.
A niddah - Because she became a niddah.
Here we have seven prohibitions. And the wording of the Mishnah:
"Haba al chamoto chayav aleha mishum chamoto" - Reuven who had relations with Basemas, who is the mother of his wife Yehudis.
"Vechalato" - Because she was married to Chanoch, his son from another marriage.
"Va'achot ishto" - Because she is the sister of his wife Yehudis, since they share one father, Yishmael.
"Ve'eshet achiv" - Because she was married to Shimon, his brother.
"Ve'eshet achi aviv" - Because she was married to Esav, his father's brother.
"Ve'eshet ish" - Because she is still married.
"Veniddah" - Because she became a niddah. These are seven.
"Vechen haba al em chamoto ve'al em chamiv" - And similarly, one who has relations with his mother-in-law's mother and with his father-in-law's mother:
Here too, it is possible to establish a situation where the woman is forbidden in seven ways, whether as Reuven's mother-in-law's mother or as his father-in-law's mother. We will examine the various family trees.
The Second Case - His Mother-In-Law's Mother:
The family tree: Lavan has a daughter named Leah; Leah has a daughter named Dinah, making her Lavan's granddaughter; and Lavan has a daughter named Serach with Dinah. Reuven marries Serach, meaning that his mother-in-law is Dinah, and his mother-in-law's mother is Leah. Because of this, Leah is forbidden to him in two ways:
His mother-in-law's mother - as she is the mother of his mother-in-law, Dinah.
His wife's sister - because Leah's father is Lavan, and Serach's father is also Lavan, who had her with Dinah.
From here onward are the five familiar prohibitions: Leah marries Chanoch, Reuven's son from another marriage, and the marriage dissolves, but she remains his daughter-in-law forever; after that she marries Shimon, Reuven's brother, and becomes his brother's wife forever; after that she marries Asaf, Reuven's father's brother; and she is still married to him - a married woman - and also a niddah. This makes seven.
The third case - his father-in-law's mother:
Here the two people are Leah and Levi. The family tree: Keturah has a daughter named Leah; Leah has a son named Reuven, who is Keturah's grandson; and Keturah and Reuven have a daughter named Dinah; and Levi marries Dinah. Once Levi marries Dinah, Leah becomes forbidden to him in two ways:
His father-in-law's mother - Dinah is Levi's wife, Reuven is her father and therefore his father-in-law, and Leah is Reuven's mother.
His wife's sister - Leah's mother is Keturah, and Dinah's mother is also Keturah.
Once again, the five familiar stages join in: Leah marries Chanoch, Levi's son from another marriage, and becomes his daughter-in-law; after that she marries Shimon, his brother; after that she marries Eisav, his uncle, his father's brother; and she is still married to him - a married woman - and also a niddah. This gives the same total of seven.
The dispute between Rabbi Yochanan ben Nuri and the Sages:
This concludes the first part of the Mishnah, and now a new point arises. Rabbi Yochanan ben Nuri holds that one can set up a family tree where a person is liable for one act of intimacy with one woman due to three different prohibitions: his mother-in-law, his mother-in-law's mother, and his father-in-law's mother - the three prohibitions listed in the first part of the Mishnah.
The family tree: Zilpah has three children - Leah, Rachel, and Asher; Leah has a daughter named Yocheved, and Asher has a daughter named Serach. This means that Zilpah is the grandmother, and she has three children and two granddaughters. Now Kalev comes and marries the three women in the story - Rachel, Yocheved, and Serach:
He married Rachel, Zilpah's daughter, making Zilpah his mother-in-law.
He married Yocheved, Leah's daughter, making Leah his mother-in-law and Zilpah his mother-in-law's mother.
He married Serach, Asher's daughter, making Asher his father-in-law and Zilpah his father-in-law's mother.
Thus, there are three relationships between Kalev and Zilpah: his mother-in-law, his mother-in-law's mother, and his father-in-law's mother. And Rabbi Yochanan ben Nuri says that just as in the other cases, here too he would be liable for three separate chatas offerings. On this point the Sages disagree with him, and the halachah follows the Sages.
The Source of the Prohibitions:
The foundation of the dispute is the question: From where do we know that one's mother-in-law, his mother-in-law's mother, and his father-in-law's mother are prohibited under the penalty of kares? The answer is that this is derived from an exposition, since the verse itself speaks of the generations below. It states: "You shall not uncover the nakedness of a woman and her daughter" - that he may not have a mother and a daughter; and it states: "You shall not take her son's daughter, or her daughter's daughter, to uncover her nakedness" - going down to the next generation, to the granddaughters through the son and through the daughter; and it further states: "They are her near kinswomen; it is depravity".
From the verse it is expounded that we do not merely go down one generation to the granddaughters from both directions, but we also go up generations above: not only to the mother, but to the mother-in-law, and from there to the mother-in-law's mother and the father-in-law's mother. In other words, one who marries a daughter is prohibited to her mother - who is his mother-in-law - and even to the generation above her, to his mother-in-law's mother and to his father-in-law's mother.
These three prohibitions - a mother-in-law, a mother-in-law's mother, and a father-in-law's mother - are all derived from the same verse, and not one of them is explicitly stated in the text, but rather it is all an exposition. From here they disagree:
Rabbi Yochanan ben Nuri: Since we derived all three of them, each one is a separate negative commandment, and one is liable to kares for each and every one. Therefore, if the situation is structured in such a way that all three apply to one woman, he is liable to three chatas offerings.
The Sages: Since the matter is not explicit, and the three different prohibitions - a mother-in-law, a mother-in-law's mother, and a father-in-law's mother - are all derived from the same teaching and the same verse, from a single source, they are all considered to be one prohibition. Therefore, even if he violated all three of them at once, he is only liable to one chatas offering. This is the principle of one inclusive category as opposed to separate, individual prohibitions.
And the wording of the Mishnah is:
"Rabbi Yochanan ben Nuri omer: Haba al chamoto chayav aleha mishum chamoto" - this is the first prohibition.
"Ve'em chamoto" - if it turns out that she is also his mother-in-law's mother, like Zilpah, the mother of Leah.
"Ve'em chamiv" - if it turns out that she is also the mother of his father-in-law, Asher. He is thus liable for three.
"Amru lo: Shelushtan shem echad hen" - the Sages reject his words: they are one category, one classification, since they are all derived from the same verse and there is no explicit mention for each relationship on its own as a separate prohibition; rather, they are all bound together.
Therefore, even one who violates all three of them at once is only liable to one chatas offering alone - and such is the halachah.