Question: What is the source that if Reuven had Bi'ah b'Mezid with Achos Ishto, Reuven is not forbidden to his wife (Leah)?

Answer (Beraisa): "Osah" - Leah is forbidden through her own Bi'ah (with a man other than her husband), but not through Bi'ah of her sister (with Reuven).

If not for the verse, we would have learned a Kal va'Chomer:

In a light Isur Bi'ah (Eshes Ish), the Oser (one who forbids, i.e. her husband forbids her to all men) becomes forbidden. All the more so, in a severe Isur Bi'ah (Achos Ishto), the Oser (Leah, who forbids her sister to Reuven) should become forbidden!

R. Yehudah says, Beis Shamai and Beis Hillel agree that one who has Bi'ah with Chamoso (his mother-in-law) becomes forbidden to his wife. They argue only about Bi'ah with Achos Ishto;

Beis Shamai say, this forbids his wife;

Beis Hillel say, it does not.

R. Yosi says, Beis Shamai and Beis Hillel agree that one that has Bi'ah with Achos Ishto permitted to his wife. They argue only about Bi'ah with Chamoso:

Beis Shamai say, this forbids his wife;

Beis Hillel say, it does not.

(Bi'ah with Achos Ishto does not forbid because) initially, Reuven was permitted to all women, and Leah was permitted to all men. After he was Mekadesh her, he forbids her and she forbids him:

He forbids her more than she forbids him. He forbids her to all men in the world, and she only forbids him on her relatives.

We learn from a Kal va'Chomer. He forbids her to all men, yet Bi'ah b'Shogeg with someone forbidden to her does not forbid her to (her husband, to) whom she was permitted;

She forbids him only to her relatives. All the more so Bi'ah b'Shogeg with someone forbidden to him does not forbid him to one to whom he was permitted!

Question: This teaches about Shogeg. What is the source if he sinned b'Mezid?

Answer: "Osah" - she is forbidden through her own Bi'ah, but not through Bi'ah of her sister.

Question: What is R. Yehudah's reason?

Answer (Reish Lakish) Question: "You will burn he and them" - do we burn everyone (even his wife, who did not sin)?!

Answer: The verse cannot teach that she is burned. Rather, it teaches that she is forbidden.

(Rav Yehudah): The Halachah does not follow R. Yehudah.

A man had Bi'ah with his mother-in-law; Rav Yehudah lashed him.

Rav Yehudah: Had Shmuel not taught that the Halachah does not follow R. Yehudah, I would forbid you to your wife permanently.

Question: The Beraisa (1:c:1) mentioned a light Isur. What is it?

Answer #1 (Rav Chisda): It is Machazir Gerushaso after Nisu'in with another man;

When the latter husband had Bi'ah with her, this forbade her to the first husband. When the first remarried her and had Bi'ah with her (after the second divorced her), he forbade her to the second (the second transgresses Machazir Gerushaso if he remarries her).

Rejection: One cannot learn a Kal va'Chomer from Machazir Gerushaso (to say that Bi'ah with Achos Ishto forbids Ishto), for Machazir Gerushaso is more stringent:

Her body was defiled;

The Isur can come through any man (Tosfos. Rashi deletes this from the text);

The Isur is permanent (but Achos Ishto is permitted after Ishto dies).

Answer #2 (Reish Lakish): It is a Yevamah.

Question: To whom is the Isur?

Answer #1: It is to a stranger, like Rav Hamnuna taught:

(Rav Hamnuna): If a Shomeres Yavam had Bi'as Zenus she is forbidden to her Yavam.

Rejection: One cannot learn a Kal va'Chomer from a Yevamah who had Bi'as Zenus. That case is more stringent (than Achos Ishto):

Her body was defiled;

The Isur applies to all men.

Answer #2: It is a Yevamah forbidden to the brothers:

If Reuven gave to her a Ma'amar, he forbids her to the other brothers. If Shimon then had Bi'ah with her, he forbids her to Reuven.

Question: Why does the Beraisa say that Bi'ah with the light Isur (forbids the Oser)? Even if Shimon gave to her a Ma'amar, he forbids her to Reuven!

Answer: The Beraisa is R. Gamliel, who says that a Ma'amar does not take effect after a Ma'amar.

Rejection: Still, Shimon can forbid her through giving her a Get or doing Chalitzah!

Answer #3 (R. Yochanan): It is a Sotah.

Question: To whom is the Isur?

Answer #1: It is to her husband.

Rejection: Why does the Beraisa say that Bi'ah with the light Isur forbids (the Bo'el (suspected adulterer), who forbade her to her husband)? Even if her husband divorced her, or said that he will not give her to drink, she is (permanently) forbidden to the Bo'el!

Answer #2: The Isur is to the Bo'el.

Rejection: This is not a light Isur. It is the severe Isur of Eshes Ish!

Answer #4 (Rava): It is an Eshes Ish.

Question: Why is this called a light Isur?

Answer: The Oser does not forbid her his entire life.

Support - (Beraisa - Aba Chanan) Suggestion: Eshes Ish is a light Isur, for the Oser does not forbid her his entire life. One who has Bi'ah with her forbids her to the Oser. If one has Bi'ah with a severe Isur, in which the Oser forbids her his entire life, all the more so he should forbid her!

Rejection: "Osah" - Bi'as Zenus of an Eshes Ish (Leah) forbids her, but Bi'ah of Leah's sister (with Leah's husband) does not forbid Leah (to her husband).

(Mishnah - R. Yosi): Anyone who forbids others forbids to himself. Anyone who does not forbid others does not forbid to himself (this will be explained).

Question: What does this mean?

Suggestion: The first Tana said that if Reuven's wife Leah and Giso (David, the husband of Leah's sister Rachel) went overseas (and we heard that they died and Reuven married Rachel), David's wife becomes forbidden to David, and Reuven's wife is permitted (to Reuven). R. Yosi says, just like Reuven's wife is permitted, David's wife is permitted.

Rejection: If so, he should have said 'anyone who does not forbid to himself does not forbid to others', and not 'anyone who does not forbid others does not forbid to himself'!

Answer: Rather, just like his (David's) wife is forbidden, also Reuven's wife is forbidden.

Question: This explains 'anyone who forbids to others forbids to himself'. How do we explain 'anyone who does not forbid to others does not forbid to himself'?

Answer #1 (R. Ami): This refers to the Reisha (87b). A woman who married according to Beis Din must leave her husband, and she is exempt from a Korban. If she married based on (two) witnesses, she must leave (her new husband, but she is permitted to her first husband), and she must bring a Korban. Great is the power of Beis Din that exempts her from a Korban;

The first Tana says, whether Reuven married Achos Ishto based on witnesses [that her husband died] and she remains permitted to her husband; or whether he married her according to Beis Din, and she is forbidden to her husband, Reuven remains permitted to his wife;

R. Yosi says, when he married her according to Beis Din he forbids others, and he also forbids his own wife on himself. When he married based on witnesses he does not forbid others, and he does not forbid to himself.

Answer #2 (R. Yitzchak Nafcha): It refers to the Seifa. R. Yosi distinguishes between when Leah was Mekudeshes to Reuven and when she was Nesu'ah;

The first Tana says, whether there was Kidushin or Nisu'in, Rachel is forbidden (to David) and Leah is permitted to Reuven;

R. Yosi says, if there was Nisu'in, we are not concerned lest people say that Leah's Nisu'in was on condition. (It is clear that the marriage to Rachel was a mistake, so) he does not forbid to others (people will not say that Rachel was divorced, married Reuven, and now remarries David), and he does not forbid his wife to himself;

If there was Kidushin, we are concerned lest people say that Leah's Kidushin was on condition (and it was not fulfilled, and Reuven truly married her after David divorced her), he forbids to others (David), he even forbids to himself (Leah looks like Achos Gerushaso).

(Rav Yehudah citing Shmuel): The Halachah follows R. Yosi.

Objection (Rav Yosef): Did Shmuel really say that?!

(Rav): A Yevamah is like an Eshes Ish;

(Shmuel): She is not like an Eshes Ish.

(Rav Huna): The case is, Reuven was Mekadesh a woman and went overseas. His brother Shimon heard that Reuven died, and married her.

Rav says that she is like an Eshes Ish, and she is forbidden to Reuven. Shmuel says that she is not like an Eshes Ish, and is permitted to Reuven.

(Shmuel is not concerned lest people say that Reuven's Kidushin was conditional, and Shimon properly married her, and now Reuven marries Eshes Ach!)

Answer #1 (Abaye): Shmuel ruled like R. Yosi, but he did not say that he explains the argument like R. Yitzchak Nafcha. Perhaps he explains like R. Ami!

Answer #2 (Abaye): Even if he explains like R. Yitzchak, perhaps he rules like R. Yosi regarding 'anyone who does not forbid', but not regarding 'anyone who forbids'!