Gemara

(Mishnah): At first, one who bought Bayis Ir Chomah (a house in a walled city) would hide on the day 12 months were finished (to prevent the seller from redeeming it). Hillel enacted that the seller can leave the money in a chamber (in Beis Din), break down the door and re-enter his house. The buyer can retrieve his money whenever he wants.

Version #1 (Rava) Inference: If a man said "this is your Get on condition that you give to me 200 Zuz," she is divorced only if he willingly accepts the money from her, but not if she forces him to take it.

An enactment was needed to allow the seller to return the money to the buyer against his will. Normally, this does not work.

Objection (Rav Papa): Perhaps the enactment was needed because the buyer would hide, but if the buyer is here, the seller can return the money even against the buyer's will!

Version #2 (Rava) Inference: If a man said "this is your Get on condition that you give me 200 Zuz," if she gives the money she is divorced, whether or not he accepted it willingly.

The enactment was needed because the buyer would hide, but if the buyer is here, the seller can return the money against his will!

Objection (Rav Papa): Perhaps it does not help to give against the buyer's will. Even if the buyer would have been there, an enactment would have been needed!

Rishonim

Rambam (Hilchos Gerushin 8:21): If a man said "this is your Get on condition that you give to me 200 Zuz within 30 days," if she gave within 30 days b'Al Korcho, it is a Pasul Get until he willingly accepts from her.

Rosh (Gitin 7:7): Rava did not teach about giving a free gift b'Al Korcho. Obviously, one does not acquire b'Al Korcho! Obviously, one can pay a debt or return a deposit b'Al Korcho in a settled area. He discusses something that Ploni must receive from Almoni, and Almoni has rights in a corresponding matter, e.g. a Get on condition that she give 200 Zuz or Bayis Ir Chomah. Rava was not concerned for Rav Papa's question, for he holds that if Nesinah is even b'Al Korcho, also in his absence it is Nesinah, and Hillel would not have needed to enact. Ba'al ha'Itur, citing Rav Hai Gaon, rules like Version #2 of Rava. He holds that Rava's opinion is primary, even though Rav Papa is Basra, because Rav Papa did not come to argue with Rava. He merely debated with him, like a Talmid in front of his Rebbi. He asked 'perhaps'. He himself was unsure. Rava saw no need to answer him. The Rambam holds that she is Safek divorced. It is good to be stringent.

Ran (Gitin 36a DH ul'Inyan) and Magid Mishneh: Ba'al ha'Itur, citing Rav Hai Gaon, rules like Version #2 of Rava. Even though Rav Papa challenged him, we do not abandon what was clear to Rava due to Rav Papa's attack, which was a mere Dichuy (a flimsy rejection). The Rambam connotes like this. He says that the Get is Pasul, i.e. mid'Rabanan, like he explained (10:2). L'Chatchilah she may not marry based on the Get. If she did, she need not leave, and the children are not Mamzerim. If he held that it is a Safek, he would have said that she is divorced and not divorced. He rules like Version #2, but he wanted to be stringent due to the severity of Ervah not to let her marry l'Chatchilah. Therefore, if one was Mekadesh 'on condition that I give to you 200 Zuz', if he gave to her b'Al Korchah she is Mekudeshes. Also for monetary laws, if one gave a house or field 'on condition that you give to me 200 Zuz', if he gave b'Al Korcho, he acquired. Others say that it is a Safek whom the Halachah follows. Therefore, for Gitin and Kidushin it is Safek divorced or Safek Mekudeshes. In monetary matters, for Metaltelim, we do not take it from the one who received. Land is in the Chazakah of the original owner.

Tosfos (Gitin 75a DH Michlal): Rava (in Version #1) does not distinguish whether or not it is in front of the receiver. In any case, it is not Nesinah. If so, why did people hide? (It would have sufficed to refuse to take the money!) We can say that in front of the seller, they would not have been brazen to refuse payment. Also, Beis Din would force them to accept.

Question: Regarding Bayis Ir Chomah, which is like paying a debt, surely it is payment! We say that one who borrowed in a settled area may not pay in a Midbar, but in a settled area he may pay even b'Al Korcho! Once one says 'take your money', he is not even a Shomer Chinam (Bava Metzia 49a).

Answer (Tosfos): Normally, it is payment, for the lender does not lose. Here, through payment he must return the house.

Question: Regarding Get, surely it is not Nesinah. One need not accept a gift!

Answer (Ri, in Tosfos): Since he said 'on condition that you give to me 200 Zuz', he made it dependent on her will, so he must accept it, and this is like Bayis Ir Chomah. Even so, b'Al Korcho it is it is not Nesinah (in Version #1).

Rambam (793, brought in Beis Yosef CM 73 DH Kasav ha'Rashba): If one swore to pay a debt on the due date, and on the day the lender was not here, he is exempt until the lender comes. He cannot make a Beis Din to accept the money. That is a special enactment for Bayis Ir Chomah.

Poskim

Shulchan Aruch (EH 143:4): If one said '(this is your Get) on condition that you give to me 200 Zuz within 30 days," if she gave within 30 days b'Al Korcho, and he did not want to accept, it is a Pasul Get until she gives with her consent.

Beis Yosef (DH Amar): It seems that the Rosh's text of the Rambam said that it is a Safek. The Rashba says that she is Safek divorced. The Rashba says that even according to the opinion that Nesinah b'Al Korcho is Nesinah, this is only to exempt the giver and to acquire what he has through fulfillment of the Tanai. This explains Get and Bayis Ir Chomah. The same applies to one who swore to give. If he gave b'Al Korcho, he was Yotzei. However, one does not receive b'Al Korcho. If one said 'give to me 100 Zuz and I will be Mekudeshes to you', and he swore to give to her, if he gave b'Al Korcho he fulfilled his oath, but she is not Mekudeshes. My Rebbi R. Yakov Bei Rav wrote that according to the opinion that Nesinah b'Al Korcho is Nesinah, there is no concern even if he did not accept it. The Chiyuv is only on the giver to give. This is like Tosfos, who said that if the seller did not hide, Beis Din would have forced him to accept. Still, this is b'Al Korcho! Rather, if he took them, even through coercion, this is Nesinah. Tosfos explains that a gift requires the Da'as (consent) of the giver and receiver, but here he made it dependent on her Da'as. It seems that the Rambam agrees. He connotes that the Get is Pasul (but mid'Oraisa, it is valid) even if he did not want to (and did not) receive it.

Beis Yosef (ibid., citing a dissenting opinion): The two versions argue only about this. Version #1 holds that Nesinah b'Al Korcho is Nesinah only if he took it, and even if he took it unwillingly. Version #2 holds that it is Nesinah as long as the giver said 'take'. This is difficult. There is no inference from Tosfos. Beis Din can force someone until he willingly accepts! Tosfos proved from Bava Metzia that Nesinah b'Al Korcho is Nesinah even if he did not take it. If he took it, surely the other has no Chiyuv Shemirah! Some tried to bring a proof from the Rambam, who says 'he did not want to accept.' I say that this does not prove that she still has the money. The Rambam did not come to teach about this. He said 'she gave to him b'Al Korcho, and he did not want to accept.' If he did not get the money, the Rambam would have omitted the words b'Al Korcho.

Beis Yosef (ibid.): I do not understand this opinion. First he said that it is difficult to say that they argue about when he did not take the money, and then brings from Tosfos that this is Nesinah! I resolve from Tosfos (75b DH Klal), who asked from R. Shimon ben Gamliel, who says that whenever she does not prevent fulfillment of the Tanai, it is a Get. This proves that Nesinah b'Al Korcho is Nesinah! R. Elchanan answered that he stipulated to receive willingly. When he changed his mind and 'did not want to accept, the Tanai was not fulfilled.' This shows that he did not take the money. If he did, Tosfos should have said 'when he accepted it b'Al Korcho, the Tanai was not fulfilled.'

Beis Shmuel (7): The Rambam holds that it is a mere stringency to say that the Get is Pasul. The Rosh and Rashba say that it is Safek divorce. This is only when she gave in front of him. Not in front of him, it is not Nesinah at all! This is clear from the Gemara. This is why they enacted to give to Beis Din.

Gra (20): The Rambam is stringent for Rav Papa's opinion.

Shulchan Aruch (CM 207:5): If a buyer or seller stipulated 'on condition that you return the item on day Ploni' or 'when he gives money', see above (120:7) whether this is Nesinah.

Darchei Moshe (1): The Ran brought two opinions about whether it is Nesinah. Therefore, if one sold Metaltelim on condition that he give, and he gave b'Al Korcho, we do not take from the buyer. If it was land, it is in the seller's Reshus.

Nesivos ha'Mishpat (Bi'urim 7): The Shach (8) said 'see Darchei Moshe. This requires investigation.' I.e. here the Darchei Moshe says that there are two opinions, but in Siman 120 all say that it is Nesinah.

Gra (16): We say that it is Nesinah, like Version #2.