Gemara

If one said that his Chatas should not be offered, all agree that it does not atone. "Yakriv Oso" teaches that it must be with his consent. (Note: this verse (Vayikra 1:3) refers to an Olah. Our Gemara understands that it applies also to Chatas.)

Erchin 21a (Mishnah): If one is obligated to bring a Chatas or Asham, we do not take a security from him. If he must bring an Olah or Shelamim, we take a security from him.

Even though "li'Rtzono" teaches that he does not get atonement until he consents to offer it, we force him until he consents.

Similarly, if one must divorce his wife, we force him until he says "I want" (and thereby authorizes Sheluchim to write and give a Get).

Kidushin 50a - Question: He was forced. He does not really want!

Answer: This shows that thoughts in the heart are ignored.

Rejection: Perhaps there is different, for it is a Mitzvah to obey Chachamim.

Gitin 88b (Mishnah): If (a Beis Din of) Yisre'elim forced a man to divorce his wife, it is valid. If Nochrim forced him, it is Pasul.

(Rav Nachman): A Get coerced k'Halachah through Yisrael is valid. If it was improperly coerced, or it was coerced k'Halachah by Nochrim it is Pasul and is Posel (disqualifies her from Kehunah). If not, it is Pasul and is Posel. If it was coerced illegally by Nochrim, it is not even Posel.

Mid'Oraisa, Nochrim cannot force us to divorce. Chachamim decreed that a Get coerced (legally) through Nochrim is Posel, lest it be confused with a Get coerced legally by Yisrael.

(Beraisa - R. Meir): "These are the judgments that you will put before them." One may not go to Nochrim for Din, even if they follow Torah law;

Bava Basra 47b (Rav Huna): If Reuven hung (or afflicted in another way) Shimon until Shimon agreed to sell his property, the sale is valid.

48a: Amidst the coercion, he decides absolutely to sell.

Question (Rav Yehudah) Why do we disqualify a Get coerced by Nochrim? We should say that amidst the coercion, he resolves to divorce!

Answer (Rav Mesharshiya): Mid'Oraisa, it is valid. Chachamim disqualified it, lest women get Nochrim to force their husbands to divorce them.

Kesuvos 86a - Question (Rav Kahana, to Rav Papa): You hold that it is a Mitzvah to pay a debt. If the borrower says 'I do not want to do the Mitzvah', what happens?

Answer (Rav Papa - Beraisa): If someone refuses to do a Mitzvas Aseh, e.g. to make a Sukah or take a Lulav, we lash him until he fulfills it or until he dies.

Rishonim

Rambam (Hilchos Gerushin 2:20): If the Halachah is that Reuven must divorce his wife, and Nochrim beat him, telling him to do like Chachmei Yisrael say, until he divorced, it is valid. If Nochrim forced him on their own, until he divorced, since he was obligated to divorce, it is Pasul. If the Halachah did not obligate him to divorce, and Beis Din erred and forced him, the Get is Pasul. Since Yisrael forced him, he resolves to divorce. If Nochrim forced him improperly, it is not a Get.

Ohr Some'ach: The Mitzvah to heed Divrei Chachamim applies only to one who observes Mitzvos, but not to an apostate. When the Mikdash stood, Beis Din could kill such people. Therefore, he would resolve to divorce, just like one who land was taken by an extortionist would agree to give it to him due to fear lest he be killed.

Tosfos (Rosh Hashanah 6a DH Yakriv): We force for every Mitzvas Aseh, like it says in Kesuvos. We need a verse for Korbanos, for one might have thought that li'Rtzono teaches that we do not force (regarding Korbanos). The Gemara says that we take security to force people to bring Olah and Shelamim, but not Chatas and Asham. All Korbanos should be the same. We should force only after he transgressed Bal Te'acher! Really, it is before, in a case that we see that he is being lazy about it (and is spending money needlessly so that he will not have left money for the Korban). If we do not find a security to take, then we force him.

Rashi (Kesuvos 91b DH Mitzvah): Beis Din does not force people to return their father's debt, for this is not an explicit Mitzvas Aseh like Sukah and Lulav. It is a mere Mitzvah mid'Rabanan.

Rebuttal (Tosfos 86a DH Pri'as): We find that we force for a Mitzvah mid'Rabanan, e.g. to fulfill the command of the deceased (Gitin 40a).

Poskim

Shulchan Aruch (EH 134:8): If Nochrim forced a man to divorce, if he was obligated to divorce, the Get is Pasul, but she is forbidden to Kehunah. If he was not obligated to divorce, she is permitted to Kehunah.

Chasam Sofer (EH 116): A man married a woman without telling her that he is epileptic. She does not want to live with him, and he refuses to divorce her. The Mordechai citing Avi ha'Ezri holds that we do not force him to divorce her, and the Rosh holds that we force him. Even if Hash-m knows that the Halachah follows the Rosh, since the Mordechai argues and we cannot decide, if one was forced to divorce, mid'Oraisa she is married. It is not a Safek. A forced Get is valid because we assume that a man wants to fulfill Divrei Chachamim. This is when the husband knows that they properly force him. Here, he can say 'who says that I must heed the Rosh? Perhaps I should heed the Mordechai!' Therefore, we cannot force him.

Nesivos ha'Mishpat (205 Bi'urim 9): The Mitzvah to heed Divrei Chachamim does not apply to a fine or one who needed to give a gift to fulfill his oath. Perhaps then he does not really want in his heart! Poskim are stringent about a Get given due to an oath (perhaps he will permit the oath!). Regarding a gift, when he says 'I want', we are not concerned lest he is insincere.

Question: The Ridvaz (on Yerushalmi Berachos 6:1) says that we do not force for a Mitzvah learned from a Kal va'Chomer. Tosfos says that we force even for Mitzvos mid'Rabanan!

Answer (Emek Halachah 1:45 DH Bi'er): Rashi says that we do not force even for Mitzvos mid'Rabanan. I agree with the Ridvaz, but for a different reason. We do not learn from a verse that we force people. It is logical, due to Arvus (Yisre'elim are guarantors for each other_. We force people so we will not be punished due to them. The Tzlach (Berachos 20) says that according to the Rambam, one cannot obligate himself in something without a limit. If so, Yisrael can obligate themselves to be Arevim for Torah laws, but not for mid'Rabanan laws. This explains Rashi. He holds that the Mitzvah must be explicit, for then it is limited. There is no limit to what can be expounded through Kal va'Chomer. This can explain why sometimes the Torah explicitly taught a law that can be learned from a Kal va'Chomer, in order that Beis Din can force for it.

Note: Sometimes we can say that the Torah explicitly taught it so Beis Din can lash for it, but lashes do not apply to all Mitzvos. Another difference is that we rebuke transgressors even if they will not listen only if it is explicit in the Torah (Rema 608:2), and one cannot become a Zaken Mamre (rebellious Chacham) for something explicit.

Emek Halachah: We force a woman to do Chalitzah only if the Yavam demands this because women do not want to marry him until he does Chalitzah. If not, we do not force her to do her Mitzvah. R. Yitzchak Elchanan (Yevamos 64) derived from this that the Mitzvah is only on the Yavam. I answer based on the Rosh (Berachos 3:13), who says that Arvus does not apply women. Therefore, we cannot force women.

Emek Halachah (2:7): For a Mitzvas Aseh, we force someone until he dies. This is only for men, but not for women. The Beraisa discusses one who refuses to make a Sukah or take a Lulav, i.e. Mitzvos that apply only to men. It did not mention eating Matzah, for also women are obligated. Rav Papa said that paying a creditor is a Mitzvah. The Gemara applied the above teaching to one who says that he does not want to do the Mitzvah. If so, how can we answer for a woman who does not want to pay her debt? I explained that we force people to do Mitzvos due to Arvus. Just like an Arev can force the borrower to pay, lest the Arev lose his money, the same applies to a Mitzvas Aseh, lest we lose through the transgressor. The Rosh and Mutzal me'Esh say that Arvus does not apply to women. Also men are not Arevim for women. Therefore, we may not force them, since they do not harm others (if they do not do Mitzvos). This applies only to a Mitzvas Aseh Bein Adam la'Makom. Surely, for a Mitzvah Bein Adam l'Chavero, such as paying debts or damage, which harm others, we force them, even though there is no Arvus.

Note: If so, we should force women regarding Chalitzah, since it affects the Yavam! Perhaps indeed, this was the Gemara's answer, that sometimes it affects the Yavam, e.g. others will not marry him until he does Chalitzah.

Emek Halachah: According to those who say that even though women are not Arevos for men, men are Arevim for women (unlike Mutzal me'Esh), we force women also due to Arvus, just like we force men. Tosfos asked why we need a verse to teach about forcing regarding Korbanos. If normally we do not force women, we can say that the verse teaches that we force a woman who vowed to bring a Korban. This shows that Tosfos holds that we force women just like we force men. However, we say that children die due to vows (of the parents). If so, surely we force women, just like for a Mitzvah Bein Adam l'Chavero, lest she cause her husband's children to die!

Note: Why do we force single women? Even if you will say that future children die due to previous vows of the parents, why do we force a woman who does not have and will not have children, e.g. she is too old, Katlanis (was widowed twice, so she may not remarry), Ailonis (does not have normal female development; she is sterile)... Perhaps since we force most women, we do not distinguish and force all women.

Emek Halachah (2:7): Tosfos could hold that we do not force women for other Mitzvos Aseh.