Gemara

23a (Mishnah #1): A woman may not be secluded with Nochrim, for they are suspected of illicit relations;

(Ravina): We are concerned for bestiality only l'Chatchilah (one may not leave animals with Nochrim, but one may buy Korbanos from them).

Question: Another Mishnah (#2) permits an Eshes Ish (a married woman) to her husband if she was taken captive by Nochrim due to money owed to her captors.

Resolution (Ravina): L'Chatchilah she may not be secluded with Nochrim, but b'Di'eved we are not concerned.

Rejection: Perhaps we are concerned even b'Di'eved. Only here, her captor fears to defile her, lest her husband not pay her debt to redeem her.

Support (Seifa of Mishnah #2): If she was taken for Nefashos (a capital charge), she is forbidden (since her captors have nothing to lose).

25a - Question: Why does the Mishnah specify Nochrim? Seclusion is forbidden even with Yisraelim!

25b - Answer: A woman may not be secluded with a Nochri even if his wife is there, for she will not guard him. A Yisraelis guards her husband.

Kesuvos 13b: R. Yehoshua said that talking (seclusion) is like a Shevuyah (a woman taken captive). Chachamim said that a Shevuyah is different, for most Nochrim are immoral.

26b (Rav Shmuel bar Rav Yitzchak): Mishnah #2 discusses only when Yisrael are in control. If the Nochrim are in control, even when taken for money she is forbidden to her husband.

Question (Rava - Mishnah): A girl was taken for collateral for a loan in Ashkelon. Her family distanced themselves from her, even though the witnesses about her abduction said that she was never secluded.

Suggestion: Nochrim are in control in Ashkelon, and she needed witnesses (that there was no seclusion) only because she was taken for collateral. One taken for ransom would be permitted without witnesses!

Nedarim 90b (Mishnah): The law was revised to say that if an Eshes Ish says 'I was defiled', she is not believed without proof.

91b: An adulterer entered a woman's house. He hid when David (her husband) came; he saw that David was about to eat poison, and warned him.

Rava: She is permitted to David. Had the man had Bi'ah with her, he would want her husband to die. We do not say that they had Bi'ah, and he wants her husband to live, for "stolen waters are sweeter."

Rishonim

Rambam (Hilchos Isurei Bi'ah 18:30): If a woman was taken for money she is permitted. When the Nochrim are in control, since she is in the Nochri's Reshus she is forbidden, unless someone testified for her, like a captive.

Magid Mishneh: 'Since she was in the Nochri's Reshus, she is forbidden' connotes that only this forbids, but not if she was willingly secluded with them. Avodah Zarah 23a connotes that we forbid due to seclusion. Sefer ha'Terumos said in the name of the Ri that in the conclusion, we do not forbid due to willful seclusion. Also the Rashba says so.

Rosh (2:2): Our Gemara concludes that l'Chatchilah and b'Di'eved are the same. An abducted woman is forbidden when the Nochrim do not fear for their money, e.g. thieves seized her or she was taken for ransom, and she does not fear for her life. Likewise, if a woman was secluded with Nochrim, we are concerned lest she was defiled. She is forbidden to Kehunah, including an Eshes Kohen. It is astounding to forbid due to seclusion with Nochrim. Rather, Ravina's law is true. The rejection is flimsy. The Reisha is not only when she was taken due to money. It applies also if she was seized by thieves or taken for ransom. B'Di'eved we are not concerned. The Mishnah discusses for money, for usually women are taken for money or Nefashos. R. Elchanan says that surely seclusion does not forbid an Eshes Kohen. Ravina teaches that b'Di'eved we are not concerned for bestiality, even if the animal was with the Nochri many days. We bring a proof from an Eshes Kohen who was abducted and in the Nochri's house many days. The Gemara rejects this. An abducted woman is permitted because her captor fears to lose his money, but if he had no monetary claim against her or her husband, she is forbidden even b'Di'eved. Likewise, we are concerned for bestiality if the animal was with the Nochri many days. Surely, when she is not under the Nochri's control he is afraid, and we do not forbid her due to seclusion.

Ran (Kesuvos 11a DH Ela): The Gemara connotes that when the Nochri does not fear losing his money, she is forbidden through seclusion. This is wrong. The Ri explained that the Gemara rejects Ravina and forbids buying an animal from a Nochri for a Korban. We permit an abducted woman because the Nochri fears to lose his money. We do not forbid a woman due to seclusion, for she is not under his control. It seems that the Rambam agrees. When the Nochrim are in control, even if she was taken due to money, since she was in his Reshus, she is forbidden.

Rosh (Yevamos 2:8): We forbid a woman to her husband only through witnesses of Zenus. Rumors forbid her only to the suspected adilterer (if he later married her), even if they were secluded for Zenus. In Nedarim, Rava needed a reasoning to permit only because she claimed that she was defiled.

Tosfos (23a DH v'Su): If we would forbid even a Penuyah to Kehunah for willful seclusion with a Nochri, no Eshes Kohen could remain married! Ravina is correct; the rejection is flimsy. Or, seclusion is unlike abduction. A secluded woman can scream and people will save her, so the Nochri is afraid. The Yerushalmi permits even a deafmute, for she can gesture.

Tosfos (Kesuvos 13a DH Ma'aleh): Our Gemara connotes that we forbid a Penuyah (to Kehunah) due to seclusion, but not an Eshes Ish. Nedarim 91a connotes that we forbid even an Eshes Ish (Rava needed a special reason to permit)! There, he discusses an adulterer. R. Yosef explains that we do not forbid a secluded Penuyah to the man's son, according to R. Yehudah who forbids a man to a girl with whom his father had Bi'ah.

Poskim

Rema (EH 7:11): If a woman was secluded with a Nochri, even if she owes him money, we do not forbid due to seclusion, even though she did improperly. Even if there are rumors of Zenus, we are not concerned for rumors after Nisu'in to forbid to her husband.

Beis Yosef (DH v'Chosav ha'Ran): The Ran, Magid Mishneh, Tosfos, Rashba and Rosh hold that seclusion does not forbid. A case occurred in which Reuven owed money to a Nochri, and he went away. The Nochri ate, drank and slept in the house with Reuven's wife. The Nochri was in control. There was suspicion about Reuven's wife. The Rosh (Teshuvah 32:7) said that we are not concerned for it to forbid her. We hold that we do not forbid due to seclusion (Kesuvos 13a). This is unlike a woman taken into the Nochri's house for collateral. Since the Nochrim are in control and he does not fear losing his money, she is forbidden. Here, she was not taken. Even if she is an Eshes Kohen, she is permitted.

Rema: However, if she was secluded for Zenus, one should be stringent (Maharik 160).

Chelkas Mechokek (22): If the Maharik means that one should be stringent to forbid her to her husband, this is unlike Kidushin 81a which says that we do not forbid due to seclusion, unless her husband warned her not to be secluded with him. The Mechaber (178:6) does not forbid due to seclusion for the sake of Ervah (there he does not discuss Nochrim - PF). If the Rema discusses an Eshes Kohen, why is seclusion for the sake of Zenus different? We are concerned for rape only when she is under his control! Darchei Moshe (13) left this difficult. I say that Maharik discusses a Penuyah talking obscenely with a Nochri, and she was secluded for the sake of Zenus. We forbid her to a Nochri. He does not discuss an Eshes Ish. If an Eshes Ish was secluded, we do not distinguish an Eshes Kohen from an Eshes Yisrael. The lenient opposite permits even an Eshes Kohen. The Re'em is concerned for rape in any seclusion, even not for the sake of Zenus. Maharik says that this is unlike all the Poskim.

Beis Shmuel (34): The Maharik cites Semag in the name of Bahag that a woman secluded with a Nochri is like a Shevuyah, and she is forbidden to Kehunah. He learns from Kesuvos 13b that seclusion is like a Shevuyah. R. Gamliel argues, for most Nochrim are immoral. This shows that he agrees that seclusion with a Nochri forbids, like a Shevuyah! Maharik said that Bahag can agree with all the Poskim who permit one who was secluded. They discuss an Eshes Ish, but a Penuyah is forbidden. Or, Bahag discusses one who was secluded after obscene talk. Chelkas Mechokek holds that both answers discuss a Penuyah. They argue about whether we forbid only if they were talking obscenely beforehand. This is wrong. Maharik's second answer discusses an Eshes Ish. Maharik and the Darchei Moshe say that one may rely on most Poskim without permit an Eshes Kohen who was secluded, if it was not for Zenus. However, the Mechaber (178:6) permits even seclusion for Zenus! The concern is for willful Zenus, and Maharik does not distinguish Yisraelim from Nochrim! Perhaps Maharik forbids then even with a Yisrael, and we hold like him only regarding a Nochri. Or, perhaps Maharik is a mere stringency of lineage regarding Kehunah, even though the concern is due to willful Zenus, since it is only a Safek, and we do not forbid to her husband due to a Safek. Seclusion for the sake of Zenus is like a Shevuyah, who is considered Vadai defiled regarding Kehunah. The Rema rules like this.

Gra (40): Seclusion for the sake of Zenus is like seclusion after warning. It forbids, for there are Raglayim l'Davar (grounds to believe) that there was Zenus (Sotah 2b).