Gemara

(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. Nochrim beat him, telling him to do like Chachmei Yisrael say.

(Rav Nachman): A Get coerced legally (i.e. when he is obligated to divorce) by Yisre'elim is valid. If it was illegally coerced, it is Pasul and is Posel (disqualifies her from Kehunah).

If it was coerced legally by Nochrim, it is Pasul and is Posel. If it was coerced illegally by Nochrim, it is not even Posel.

Question: If Nochrim have the power to force us to divorce, a legally coerced Get should be valid. If they have no such power, it should not be Posel!

Answer #1 (Rav Mesharshiya): Mid'Oraisa, a Get legally coerced by Nochrim is valid. Chachamim decreed that it is Pasul, lest women who want to be divorced get Nochrim to coerce their husbands.

Objection: If so, a Get coerced illegally should be Posel, like a Get coerced illegally by Yisre'elim!

Rav Mesharshiya's answer is wrong.

Answer #2: Mid'Oraisa, a Get legally coerced by Nochrim is Pasul. Chachamim decreed that it is Posel, lest it be confused with a Get coerced legally by Yisrael. A Get coerced illegally by Nochrim will not be confused with a Get coerced legally by Yisrael, so there is no need to decree.

Rav Yosef was forcing a man to give a Get.

Question (Abaye): We (Chachamim of Bavel) are like commoners. We cannot coerce to divorce!

(Beraisa - R. Meir): "These are the judgments that you will put in front of them" - one may not go for judgment in front of Nochrim, even if their law (in the case) is the same as Torah law;

Also, "in front of them (Mumchim, i.e. expert judges)", not in front of commoners.

Answer (Rav Yosef): We are Sheluchim (to coerce Gitin) on behalf of the Mumchim in Eretz Yisrael, just like we are their Sheluchim to judge cases of admissions (of debt) and loans.

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 - Mishnah): If (a Beis Din of) Yisrael forces a man to divorce his wife, it is valid. If Nochrim force him, it is invalid. Nochrim beat him and say 'do what Beis Din of Yisrael tell you.'

Why is it invalid when Nochrim coerce (on their own)? We should say that amidst the coercion, he decides absolutely to divorce!

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

Rishonim

Rif and Rosh (9:10): A Get coerced legally by Nochrim is Pasul and is Posel. If it was coerced illegally by Nochrim, it is not even Posel.

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.

Kesef Mishneh: Rashi says that Rav Mesharshiya is rejected because surely Nochrim cannot force a Yisrael to divorce, and the Get is Batel mid'Oraisa. Chachamim enacted that the Get is Pasul lest people think that even Beis Din cannot coerced Gitin. Rav Nachman's words 'it is Pasul and it is Posel' support this. It is a Get only to disqualify from Kehunah. Why does the Rambam say that it is Pasul, i.e. mid'Oraisa it is valid? Rav Mesharshiya was rejected! Perhaps he holds that since we rely on his answer in Bava Basra (48a), this shows that the Halachah follows him. This is difficult. We rely on where his law was taught (Gitin). Even if we were concerned for the other Sugya, she would be Safek Megureshes; if she remarried, she must leave!

Question (Lechem Mishneh): The Rambam is unlike either Sugya! In Gitin, the Get is Batel mid'Oraisa. If he rules like the other Sugya, why is a Get coerced improperly by Yisrael Pasul, i.e. Kosher mid'Oraisa? Also, why are Nochrim different than Yisraelim? Both of them have power to coerce!

Answer (Lechem Mishneh): Really, he holds like the Sugya in Bava Basra. The Gemara equates coercion to divorce with coercion to sell. If amidst coercion to sell he agrees for the money, we should say that amidst coercion to divorce he agrees for the Mitzvah. This is even when Nochrim coerce, and the only Mitzvah is to divorce. The questioner held that neither of these suffices, unless Beis Din coerces to divorce, for then there is also a Mitzvah to heed Chachamim. Rav Mesharshiya answered that a Get properly coerced by Nochrim is Kosher mid'Oraisa. They have no authority to coerce, but it is a Mitzvah to divorce. Similarly, a Get improperly coerced by Beis Din, in which there is also one Mitzvah (to heed Chachamim), is Pasul mid'Rabanan. If a lone Yisrael coerces, since he is not a Beis Din, this is like Nochri who coerces. The Gemara in Gitin rejected Rav Mesharshiya because it misunderstood him. However, since we equate a coerced Get to a coerced sale, we should require that he says 'I want.' The Rambam says that coerced Kidushin is valid, and did not mention this!' Perhaps the questioner equated a coerced Get to a coerced sale, but the conclusion does not.

Rosh: R. Tam explained that the Seifa, 'Nochrim beat him, telling him to do like Chachmei Yisrael say' refers to the previous clause, which disqualifies this, for Nochrim may not be used to coerce. R. Tam retracted to explain that it teaches how it is Kosher through Nochrim? They beat him, telling him to do like Chachmei Yisrael say.' When Nochri judges force, we apply "in front of them", but not in front of Nochrim. Yisrael judges may force through Nochrim. Before Abaye knew that we are Sheluchim to coerce Gitin on behalf of Mumchim in Eretz Yisrael, surely he did not think that the Mumchim themselves must beat the husband! Therefore, even when Nochri beat him, it is as if the Mumchim beat him. The Tosefta supports this. The Yerushalmi derives from our Mishnah that when the Nochri says 'do what they say, not what I say', it is Kosher. Rav Huna taught that a coerced sale is valid. Amidst the coercion, he resolves to sell. We challenged him from our Mishnah. Why didn't we support him from the Reisha? If this is because it is a Mitzvah to heed Chachamim, like we said there to reject a support from a Beraisa, this applies also when Nochrim force him to do obey Chachamim! (If this is Pasul, the Gemara should have challenged the Mishnah itself!) Rather, also this is Kosher. We asked why when Nochri judges coerce, it is Pasul. (I.e. we do not say that amidst the coercion, he decides to divorce!)

Poskim

Shulchan Aruch (EH 134:8): If Nochrim forced one 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.

Shulchan Aruch (9): If a Beis Din of Yisre'elim pressured him through Nochrim, who beating him, saying 'do like Yisrael tell you', it is as if Yisre'elim forced him.

Beis Shmuel (15): It suffices if they say 'give a Get', since Yisre'elim said so.