Gemara

65b (Mishnah): Levi may lend to David on condition that if the loan is not paid within three years, Levi will keep David's field. Chachamim sanctioned Baisus ben Zunin to do so.

66a (Rav Huna): If the Tenai was made when the money was given, it is binding (even if the field is worth more than the loan). If the condition was made afterwards, Levi gets land only according to the amount of the loan.

(Rav Nachman): Even if the Tenai was made afterwards, it is binding.

Retraction (Rav Nachman): Even if the Tenai was made when the money was given, it is void. I used to hold that Asmachta (an exaggerated promise) acquires. Minyomi convinced me that it does not.

Question: The Mishnah refutes Minoymi!

Answer #1: The Mishnah is R. Yosi, who says that Asmachta acquires (but Chachamim argue).

Answer #2: The case is, the borrower said 'acquire it from now (on condition that I do not pay in time)'.

Question (Mar Yanuka and Mar Kashisha, sons of Rav Chisda): In Neharda'a, they cite Rav Nachman to say that Asmachta acquires (when he does not pay up) in the (set) time. Not in the time (rather, before it) it does not acquire!

Objection (Rav Ashi): Any Kinyan acquires only at the proper time!

Answer (Rav Papa): If David is particular about land, Levi acquires.

Rav bar Sheva owed money to Rav Kahana. He fixed a date, and said 'if I don't pay by then, you can collect from this wine.'

(Rav Papa): Asmachta does not acquire only regarding land, for it is not destined to be sold. Wine is destined to be sold, so it is like money!

Objection (Rav Huna brei d'Rav Yehoshua): Rava said that any (promise starting with) 'if' does not acquire.

73b (Rav Chama): If a Shali'ach received money to buy wine, and he was negligent and did not, he must give wine like the (low) major market price.

(Rav Ashi): He just gets back his money. Even if he promised to give his wine if he will not buy, this is only Asmachta. There was no acquisition.

This is unlike one who rented a field on condition to give a certain amount if he will not work the field (which is binding). There, he can surely work the field. Here, there is no guarantee that they would sell to him.

Nedarim 27a (Rav Huna): If one had documents in his favor in Beis Din, and said 'if I do not return within 30 days, these proofs should be void', and an Ones prevented him from returning in time, his proofs are void.

Question: Rav Nachman said that the Halachah does not follow R. Yosi, who says that Asmachta acquires!

Answer: Here is different. Since he said that the proofs should be void, this is like an admission that they are invalid.

The Halachah is, Asmachta acquires when there is no Ones, and they acquired from him in a respected Beis Din.

Rishonim

Rif and Rosh (5:29): In our Mishnah, he said 'from now.' If not (rather, he said if...), it would be Asmachta, and it does not acquire.

Rosh: In other cases of Asmachta, even if he said 'from now', it acquires only if it was in an esteemed Beis Din (Nedarim 27b). 'They acquired from him' connotes Chalipin, which can only be from now, but not after the garment was returned. Here is different, for from the beginning the Mashkanta resembled a sale. The lender received the field to use. Also, the borrower benefitted from the lender. Therefore, he intended to fulfill his promise. Surely, this Asmachta is different than others. Here, Rav Nachman retracted only due to Minyomi. In Bava Basra (168a) and Nedarim, he ruled unlike R. Yosi! R. Tam says that here is different because the lender has possession of the field.

Rambam (Hilchos Mechirah 11:2): If one acquired through a valid Kinyan, and Tana'im were made, the Kinyan is valid only if they were fulfilled. If he did not acquire now and stipulated that he will acquire only if he fulfills the Tenai, even if he fulfilled it he did not acquire, for this is Asmachta.

Rambam (3): If one sold or gave a house on Tenai that Levi go with him to Yerushalayim on a certain day, and Levi made a Chazakah in the house from now, he acquires only if he goes on that day. However, if he stipulated 'if you will go with me on this day or give a certain item to me, I will give this house to you, or sell it for this amount', and Levi went on that day or gave the item, even if he did Chazakah in the house afterwards, he did not acquire. This is Asmachta, for he attributed the Kinyan to doing the action. It does not acquire, for he did not resolve in his heart to transfer ownership. The same applies to all similar cases.

Rambam (7): Whoever says 'acquire from now', it is not Asmachta at all, and he acquires. Had the giver not resolved to transfer ownership, he would not have given from now. If he said 'if I come from now until such and such day, acquire the house from now' and a Kinyan was done, he acquired if he came in the time. The same applies to all similar cases.

Rosh (5:30): We conclude that Asmachta acquires only if David is particular about land, i.e. from the beginning he was insistent not to give any other land for collateral. Why did the Rif omit this? Rava said that any 'if' does not acquire, but Rav Papa says that he acquires in this case. The Halachah follows him, for he is Basra! We conclude that Asmachta does not acquire, even if he said 'acquire for collection', and even if it is not exaggerated. Even though people often sell land to pay debts, since people do not willingly sell land, it is considered exaggerated. We say that Asmachta does not acquire wine because people do not normally sell it before the proper time, when it sells for more.

Poskim

Shulchan Aruch (YD 174:1): If Reuven sold a field to Shimon and said 'when I will get money, return the land to me', Shimon did not acquire, and all the Peros he eats are Ribis. If Shimon told him on his own 'when you will have money, I will return the land to you', it is not a Tenai and Shimon acquires immediately, therefore, he eats the Peros. If when Shimon said this Reuven strengthened it, it is a Tenai. If Shimon stipulated, even amidst the sale, and Reuven was silent and did not strengthen it, it is not a Tenai. It is Pitumei Mili. The sale is valid, since Reuven, who should have stipulated, did not do so.

Shach (2): If he said so at the beginning of the sale, even if the buyer said so it is a valid Tenai.

Gra (3): This is like Rashi and the other Poskim. The Rambam explains differently, like we wrote in CM 207.

Shulchan Aruch (CM 207:1): If one was Makneh land or Metaltelim, and the giver or buyer stipulated Tana'im, he acquires only if they are fulfilled.

SMA (CM 207:6): It sounds like the Rambam (and Tur) distinguish(es) between whether or not he acquired immediately. The Beis Yosef says so. I proved that even if the Kinyan was immediately, since the Kinyan was on Tenai, it is Asmachta unless he acquired from now. The Rambam holds that 'from now' is Mevatel Asmachta. Perhaps this is why Ir Shushan says 'he acquired from him from now.' However, the Rambam did not mention 'from now' until Halachah 7! Also, the Rambam explains that the Tenai works when he says 'on condition that', but it is Asmachta when he said 'if'. Also, he says 'this is Asmachta, for he attributed the Kinyan to doing the action.' He did not say that it is Asmachta because he did not transfer ownership from now! Rather, the Rambam distinguishes as follows. When the seller wanted to sell the item, just he wanted the Tenai to be fulfilled, this is like the Tenai with Bnei Gad and Bnei Reuven. It is not Asmachta, and it acquires. If his primary intent is fulfillment of the Tenai, but the other party will do so only if he will get the field, this is Asmachta.

Shach (2): This requires investigation. See the Maharshach.

Maharshach (2:163): A case occurred in which Moshe sold to Yosef a quantity of wool, to be given at the time of shearing. The document said that if he lacks it, he is obligated to buy it to give to Yosef. The price skyrocketed. This is not Asmachta, for his primary obligation was to give wool, just he must buy if he lacks. This is unlike the Shali'ach who was negligent and did not buy wine. It was not b'Yado (perhaps they would not sell to him). Here, Moshe could have bought. Also, even the word 'Kinyan' removes Asmachta, all the more so here, where they stipulated that he is obligated.

Gra (5): The Rambam holds like Rav Hai Gaon, who says that any 'if' is Asmachta, for it should not take effect from now.