Gemara

(Mishnah): If Reuven gave a Perutah of Hekdesh to a Balan (bathhouse attendant), Reuven is Mo'el immediately, for he may bathe whenever he wants.

Bava Metzi'a 44a (Mishnah): If Reuven paid for Shimon's Peros and did not yet do Meshichah, Shimon can retract. However, Chachamim said 'He (Hash-m)... will punish one who does not honor his word.'

47b (R. Yochanan): Mid'Oraisa, money acquires Metaltelim;

Chachamim enacted that (only) Meshichah acquires, lest one sell something in his house, and a fire will erupt through Ones. The seller will strive to save it only if it still belongs to him.

(Reish Lakish): "Kanoh mi'Yad Amisecha" refers to something that is passed from hand to hand. This teaches that Meshichah (and not Kesef) acquires.

R. Yochanan explains that "mi'Yad" excludes land from the law of Ona'ah.

48a (Rava): A verse supports Reish Lakish - "and he will deny to his colleague a deposit, bi'Seshumes Yad... or Oshak..."

(Rav Chisda): "Seshumes Yad" is a security for a loan. "Oshak" is a security for wages.

Regarding admission, it says "he will return... ha'Oshek...", but it does not mention Teshumes Yad!

Suggestion: This is because the lender need not return it, for he never acquired it, for he never did Meshichah!

Question (Rav Papa): Perhaps the Torah need not say that he returns it, because we learn from Oshek!

(Rava): Also a Beraisa supports Reish Lakish.

(Beraisa): If Reuven gave to a Balan, Reuven transgressed Me'ilah;

(Rav): This refers only to a Balan, for no Meshichah is required. When Meshichah is required, there is no Me'ilah until Meshichah. (It completes the transaction.)

Support - Contradiction: A Beraisa teaches that if Reuven gave Hekdesh money to a barber, Reuven transgressed Me'ilah. Another Beraisa teaches that Me'ilah is only after Meshichah of the tools used to cut!

Answer: Beraisa #1 discusses a Nochri barber. Beraisa #2 discusses a Yisrael barber.

(Rav Nachman): Money acquires mid'Oraisa.

Rishonim

Rif (Bava Metzi'a 28b): R. Yochanan taught that mid'Oraisa, money acquires. We derive that if Ones occurred before the buyer did Meshichah, the seller loses. The buyer can say 'give to me the sale item, or return my money.' If the buyer rented the seller's attic, the buyer cannot retract. If an Ones occurred, the buyer loses. Chachamim enacted that Meshichah acquires, lest the seller say 'your wheat burned in the attic.' Here, it is in the buyer's Reshus. If there is a fire, he will save it himself! Even though this is according to R. Shimon, from R. Shimon we can learn to Chachamim.

Rambam (Hilchos Mechirah 3:1): Mid'Oraisa, money acquires animals and other Metaltelim. Once the buyer gave money he acquired, and neither can retract. However, Chachamim enacted that Meshichah are acquired only through Hagbahah, or Meshichah of something that is not normally lifted.

Hagahos Maimoniyos (1): This is like R. Yochanan against Reish Lakish. Also R. Tam says so, because the Halachah follows Rav Nachman in monetary laws. Also, the Halachah follows R. Yochanan against Reish Lakish with only three exceptions. Even though a verse and Beraisa seem to support Reish Lakish, R. Yochanan is not refuted. One can establish the verse like R. Yochanan. A Beraisa connotes that there is Me'ilah without Meshichah only regarding a Balan. It discusses a Nochri Balan. Regarding a Yisrael barber, there is Me'ilah before Meshichah. Rav Hai Gaon and Tosfos say so.

Rosh (Bava Metzi'a 4:8): Our Gemara teaches that if Ones occurred before Meshichah, the seller loses. The Halachah follows R. Yochanan, because Rav Nachman holds like him and the Halachah follows Rav Nachman in monetary laws. Also, in Avodah Zarah (71a) Rav Ashi concluded that Meshichah acquires for Nochrim (like R. Yochanan holds). Even though he said otherwise in Bechoros 13b, he retracted. Rava brought supports for Reish Lakish, but we hold like Rav Ashi and Ravina, for they are Basra. Also, Rava's supports for R. Yochanan were not so strong. We can say that the Torah taught that he returns Oshek (and the same applies to Teshumes Yad), and the Beraisa discusses a Nochri Balan.

Tosfos (Avodah Zarah 71a DH Pardesheni): The Ri says that even according to the opinion that money does not acquire, this is only when there is money. Regarding a (Hefker) Metzi'ah or a gift, when there is no money, all agree that one acquires through Meshichah or Hagbahah.

Shitah Mekubetzes (47b DH v'Kashya, citing the Ritva): According to R. Yochanan, how does one acquire a gift, in which there is no money? Tosfos said that R. Yochanan agrees about a gift. The Ramban says that even a gift is acquired only through Chalipin, Chatzer or Agav.

Question (Ketzos ha'Choshen CM 198:1): I do not understand this. Chazakah acquires only because it is like a Yad (i.e. putting in one's Chatzer is like putting in his hand), or due to Shelichus. According to R. Yochanan, Yad itself does not acquire (if no money was given)! Even the one who says that a Chatzer is like a Shali'ach says so only when his Yad could acquire. This requires investigation.

Poskim

Shulchan Aruch (CM 198:1): Mid'Oraisa, money acquires. However, Chachamim enacted that Metaltelim are acquired only through Hagbahah, or Meshichah of something that is not normally lifted. Once he did Meshichah or Hagbahah, he acquired even though he did not gave money.

Nesivos ha'Mishpat (Chidushim 2): When coins are not lacking, e.g. one collected property for a debt, Meshichah acquires mid'Oraisa. If Reuven's Metaltelim were in Shimon's Reshus, and Reuven told him 'give them to Levi', and Levi gave money, saying 'give' is like saying 'Zechi (acquire for)', and Reuven cannot retract. If this was in front of the buyer, also the buyer cannot retract. (This is from Sefer ha'Mekach of Rav Hai Gaon, and Machaneh Efrayim Hilchos Mechirah, Kinyan Ma'os 6).

SMA (3): If the seller was Mekadesh a woman with coins that he received from the buyer, she is Mekudeshes. We are stringent to say that Chachamim's enactment does not uproot Torah law.

Nesivos ha'Mishpat (Bi'urim 2): The SMA needed to say this (we are stringent...) only according to the opinion that the seller may not use the money. According to the opinion that the seller may use the money, because Chachamim did not uproot the seller's Kinyan of the money, we do not need this reason.

Nesivos ha'Mishpat (Chidushim 3): If the seller (retracted and) accepted the curse 'He who punished...', surely she is not Mekudeshes.

Rebuttal (Pischei Teshuvah EH 28:1): This is not clear. See Beis Shmuel (28:59, brought below, that when the seller received money through a sale, perhaps it is like a loan, so it is Safek Kidushin). If the seller was Mekadesh with the sale item, the Mishneh l'Melech (Hilchos Ishus 5:7) says that it is Safek Kidushin. Yad ha'Melech discussed a buyer who was Mekadesh with what he bought through money alone. If the seller does not retract, perhaps it is as if it was a deposit in the buyer's hand, which makes Kidushin.

Shulchan Aruch (EH 28:1): If a thief was Mekadesh with Gezel and it is known that he acquired through despair, she is Mekudeshes.

Rema: If he was Mekadesh with Gezel after despair alone, she is Mekudeshes mid'Rabanan.

Beis Shmuel (6): The Beis Yosef holds that a Kinyan mid'Rabanan makes Kidushin mid'Oraisa. The Rema holds like R. Yerucham, that it makes Kidushin mid'Rabanan, and so hold the Bach and Maharshal. It seems that the Tur in the name of the Ramah agree, but one could distinguish.

R. Akiva Eiger (Drush v'Chidush, Bava Metzi'a 48a DH Kai): Rashi says that R. Yochanan and Reish Lakish argue about one who was Mekadesh a woman. Perhaps he means that the buyer was Mekadesh with a Kli for which he paid money, but he did not do Meshichah. I.e. the Kli is in the seller's Reshus, and the buyer gave it to the woman through Chalipin. R. Yochanan holds that she is Mekudeshes. Or, perhaps all agree that she is not Mekudeshes. Rashi discusses a seller who was Mekadesh with the money he received before Meshichah was done. According to one answer in Tosfos (43b DH Mai), the seller may use the money only if money acquires mid'Oraisa. Even if Chachamim uprooted Kinyan Kesef, the seller may use the money like a borrower. Also, the seller's Kidushin with the money is valid because mid'Oraisa the money is his, but the buyer's Kidushin with the Kli is invalid because the seller can retract. Even though mid'Oraisa the buyer acquired the Kli, since the seller can retract, it is as if it is not in the buyer's Reshus. This is like Kidushin with a stolen object before the owner despaired. In practice, this requires investigation.

Dagul me'Revavah: The SMA says that we are stringent to say that the enactment does not uproot Torah law. If so, if Reuven acquired through Meshichah alone and was Mekadesh Leah, and then Shimon was Mekadesh her, she should need a Get from both of them. However, I showed (see Noda bi'Yehudah below) that Reuven can be Mekadesh mid'Oraisa.

Noda bi'Yehudah 2 EH 54, 33 DH u'Mah she'Chasav v'Im): If one acquired something (even mid'Rabanan), it is his, and he can be Mekadesh with it mid'Oraisa. The SMA said that it is a stringency to say that the seller can be Mekadesh with the money. There, Chachamim uprooted the seller's Kinyan. The buyer can retract, and the seller must return the money. When Chachamim enacted that one acquires, e.g. through Meshichah, then he can be Mekadesh mid'Oraisa. R. Yerucham was unsure about Kidushin through Ma'amad Sheloshtam, in which the woman acquires only mid'Rabanan. We cannot learn this from Kidushin with what the man acquired mid'Rabanan.

Shulchan Aruch (22): If one sold Isurei Hana'ah to a Yisrael who did not know that it is Asur b'Hana'ah, and he was Mekadesh a woman with the money, she is Mekudeshes.

Beis Shmuel (59): The Rosh and Ran say that we can say that the money is like a loan, since he received it through a sale. Bedek ha'Bayis said that this is reasonable.

Shulchan Aruch (CM 235:7): If a minor bought land and paid money and did Chazakah, he keeps it, for Zachin l'Adam she'Lo Befanav (we may do something beneficial for someone in his absence).

Ketzos ha'Choshen (4): We accept Shekalim (for Korbanos Tzibur) from minors. Mid'Oraisa they cannot give to the Tzibur. Seemingly, the Korban (brought with their money) belongs to an individual! Rather, we infer that a Kinyan mid'Rabanan helps for mid'Oraisa. The same applies to Kidushin with what was acquired through Ma'amad Sheloshtam, unlike R. Yerucham, who says that it is not Torah Kidushin.

Pischei Teshuvah (4, citing Beis Efrayim CM 8): The Poskim said that a Kinyan mid'Rabanan does not helps for mid'Oraisa only when the item is intact in the owner's Reshus. If it was given to someone else, surely the latter acquires mid'Oraisa. Chachamim's enactment is no weaker than despair and Shinuy Reshus.