Gemara

4a (Rav Sheshes): "Lo Sachsom Shor b'Disho" is followed by Parashas Yibum, to teach that we do not silence a woman who fell to Yibum to a Mukeh Shechin.

39b (Mishnah): Initially the Mitzvah of Yibum was preferable to the Mitzvah of Chalitzah. Nowadays that people do not intend for the Mitzvah, Chalitzah is preferable.

(Rav): We do not force.

When a Yavam and Yevamah would come in front of Rav, he would tell the Yavam 'It is your choice. Do Chalitzah or Yibum.' "If he does not want" teaches that if he wants, he may do Chalitzah or Yibum.

Also Rav Yehudah holds that we do not force. He enacted to write in a document of Chalitzah '...We told him 'If you want, do Yibum. If not, stick out your right foot.'

(Mishnah): Nowadays that people do not intend for the Mitzvah, Chalitzah takes precedence.

(Rami bar Chama): They returned to say that Yibum takes precedence, like Chachamim:

(Beraisa - Aba Sha'ul): If one did Yibum... for any reason (other than the Mitzvah), it is as if he transgressed Arayos. In my eyes, the child is nearly a Mamzer;

Chachamim say "Yevamah Yavo Aleha" - for any motivation.

(Beraisa): Initially, a Yevamah was permitted to her Yavam. She was forbidden (when she married his brother), and permitted again (when her husband died).

Suggestion: Perhaps she returns to her initial Heter!

Rejection: "Yevamah Yavo Aleha"- (l'Shem) Mitzvah.

(R. Yitzchak bar Avdimi): This is like Aba Sha'ul. Initially, she was permitted to him - he could marry her for beauty, or for the sake of marriage. She became forbidden, and became permitted again. She does not return to her initial Heter. "Yevamah Yavo Aleha" requires l'Shem Mitzvah.

(Rava): It can be like Chachamim. Initially, she was permitted to him - he could marry her or not. She became forbidden, and became permitted again. He does not do whichever he prefers of Yibum and Chalitzah! "Yevamah Yavo Aleha" is the Mitzvah.

Question (against R. Yitzchak): The Reisha says similarly that initially the remainder of a Minchah was permitted, it became forbidden (Hekdesh), and was permitted again (after the Kometz was offered). "Matzos Te'achel b'Makom Kadosh" teaches that it does not return to its initial Heter, rather, it is a Mitzvah.

If this is like Aba Sha'ul, what two types of eating are there?

Answer: Initially, it may be eaten as Matzos or scalded.

Kesuvos 64a (R. Pedas): We honor a demand by the Yevamah to do Chalitzah, but not a demand to do Yibum.

77a (Mishnah): If a husband has any of the following problems, we force him to divorce his wife: he is a Mukeh Shechin,... or a tanner, whether these preceded the marriage or came during the marriage;

R. Meir says, regarding all of them, even if he stipulated with her, she can say 'I thought I could bear it, but now I see that I cannot.'

Chachamim say, she is forced to bear it, except for a Mukeh Shechin, since this harms her.

A case occurred in Tzidon, and a tanner's wife fell to Yibum to a tanner. Chachamim said that she can claim, I could bear your brother, but not you.

Rishonim

Rif (12b) and Rosh (4:17): Rav and Rav Yehudah do not force; we let them decide. They returned to say that Yibum takes precedence.

Rambam (Hilchos Yibum 1:2): If the Yavam or Yevamah does not want to do Yibum, he does Chalitzah and then she is permitted. The Mitzvah of Yibum takes precedence over the Mitzvah of Chalitzah.

Rambam (2:10): If a Yevamah permitted to do Yibum does not want to, she is like one who is Moredes against her husband. We force him to do Chalitzah; she does not receive her Kesuvah.

Magid Mishnah: The Rambam (Ishus 14:8) says that we force any husband to divorce a Moredes.

Rosh (Yevamos 4:17): Rav does not force. Rashi explains that if both of them want to do Yibum, we let them. We do not say that this is like Arayos because they do not intend for the Mitzvah. The Semichus of "Lo Sachsom" to Parashas Yibum allows a Yevamah to refuse to do Yibum with a Mukeh Shechin, or for any proper reason, e.g. a tanner (he works with excrement and smells bad). Even if her first husband was a tanner, she can say that she could bear him, but not the Yavam. If he does not want to do Chalitzah, we try to trick him. E.g., we tell him to do Chalitzah and she will pay him 200 Zuz. If we cannot trick him we force him to do Chalitzah.

Rebuttal (Rosh): We cannot learn that we honor any proper reason from a Mukeh Shechin or a tanner. Beis Din forces such a man to divorce his wife if she requests! The Gemara (106a) gives several cases where she had a proper reason, and Chachamim toiled greatly to trick him. This shows that for other reasons we do not force; we only trick him. The Gemara that says that we do not write an Igeres Mered against a Yevamah holds that Chalitzah has precedence. Rashi says that nevertheless, we do not force to do Chalitzah (unless she has a proper reason). This is wrong.

Nimukei Yosef (ibid.): We expound only that we do not silence a Yevamah (who fell to a Mukeh Shechin), i.e. we do not force her to do Yibum or write Igeres Mered against her. This is no source to force him to do Chalitzah. If he does not want Yibum or Chalitzah, we force him to do one of them. Tosfos says that even if he already has a wife, and it is improper to marry a second, we do not force him to do Chalitzah. R. Shimshon imposed a Cherem not to marry a second wife, but it does not apply here, for Shomayim gave the woman to him.

Rosh (4:17): R. Tam explains that 'Rav did not force' refers to the Reisha, when Yibum was the primary Mitzvah. If they intended for the Mitzvah, Rav allowed them to do either. Also Rav Yehudah gave the option to people who came to do Chalitzah. If they do Yibum, surely it is l'Shem Mitzvah. However, normally we force to do Chalitzah, for the Halachah follows Aba Sha'ul.

Rosh (ibid.): The Ri (in Tosfos Kesuvos 64 DH v'Dinei) says that R. Tam agree that we never force to do Chalitzah. Even nowadays if they are l'Shem Mitzvah, e.g. they came to do Chalitzah, we let them do Yibum. If it is not clear that they are l'Shem Mitzvah, we verbally force them and distance them from Yibum. R. Tam agrees that if he wants to do Yibum and she does not, we do not force him to do Chalitzah, we only try to trick him. If he does not want to do Yibum or Chalitzah, we force him.

Beis Yosef (EH 165 DH v'Da): The Ri was forced to say this due to the questions against Rashi.

Poskim

Shulchan Aruch (EH 165:1): The Mitzvah of Yibum has precedence over Chalitzah. If she does not want to do Yibum with any brother (Rema - or with the oldest when he wants to do Yibum) without a proper reason, she is like a Moredes. Some say that Chalitzah has precedence.

Rema: And (therefore) she is not like a Moredes if she does not want to do Yibum. In any case we do not force him to do Chalitzah, but we trick him into doing it if possible, e.g. we tell him to do Chalitzah on condition that she will pay him 100 Zuz.

Source (Gra 7): R. Pedas taught that we do not honor a demand to do Yibum. If we force to do Chalitzah, there is no need to say this!

Rema (ibid.): This is only if he is not a kind of man whom we force him to divorce his wife if she requests. If they want to do Yibum we permit only if we know that this is l'Shem Mitzvah. Some say that if he already has a wife, we force him and excommunicate him until he does Chalitzah. Some say that even if he is single, if they are not l'Shem Mitzvah and she does not want to do Yibum and we cannot trick him, we force him.

Beis Shmu'el (1): The Rema connotes that the Rosh and R. Tam never force. This is wrong. If we do not know that they are l'Shem Mitzvah, we force verbally. According to Tosfos and the Poskim who say that 'Kefiyah' in the Gemara is always with sticks, if she vowed not to get Hana'ah from him we force him physically because there is a Vadai Isur. A normal Yibum is only a Safek (perhaps they are not l'Shem Mitzvah). If we know that they are not l'Shem Mitzvah, we force physically. According to the Poskim that Yibum is preferable, there are three laws. If we know that they are l'Shem Mitzvah, we allow Yibum. If we are unsure, we force verbally. If we know that they are not l'Shem Mitzvah, we force physically. The Beis Yosef and Darchei Moshe hold that even then case we do not force physically. Our custom is not to force physically even if we know that they are not l'Shem Mitzvah, because the Rif and Rambam say that Yibum is preferable. If he already has a wife all agree that Chalitzah is preferable, so we force physically. Perhaps this is wrong, for Yibum is not forbidden. Some say that when he has a wife we force even when we do not know his intent, due to R. Gershom's decree.

Rema (ibid.): The custom is like the first opinion, that we never force, even if we know that he desires her money. Rather, we make a compromise between them like communities enacted (Sa'if 4). This is when he wants to do Yibum and there is no concern for Isur.

Taz (2): Nowadays if he says that he refuses to do Chalitzah, it is as if he says that he will not do Chalitzah or Yibum, so we force him to do Chalitzah.

Rema (ibid.): If he does not want to do Yibum or Chalitzah we force him, but only if she has a claim (she wants children for her old age). We try to trick him into thinking that he will be paid for doing Chalitzah, to avoid needing to force him. They should not leave the money with a third party, for then they cannot tell him 'we were kidding'.

Beis Yosef (DH v'Da): The Tur says that R. Tam holds that we force to do Chalitzah. He must mean verbally, to avoid the questions against Rashi.

Darchei Moshe (1): The Radach says that when we force, it is physically. The Terumas ha'Deshen says that this is only when she has a claim (that she needs children).