Gemara

(Beraisa - Rebbi): A ship is acquired through Mesirah;

Chachamim say, it is not acquired until he does Meshichah or rents the place where it is standing.

Rebbi said that a ship is acquired through Mesirah, i.e. in a Reshus ha'Rabim. In a Simta (an area next to a Reshus ha'Rabim), Meshichah acquires.

Question: They cannot discuss a Reshus ha'Rabim, for one cannot rent a Reshus ha'Rabim! Also, Meshichah does not acquire there!

(Abaye and Rava): Mesirah acquires in a Reshus ha'Rabim, or in a Chatzer that is not of both of them. Meshichah acquires in a Simta or in their joint Chatzer. Hagbahah (lifting the item) acquires everywhere.

Answer: Chachamim mean, it is not acquired until he does Meshichah from the Reshus ha'Rabim to a Simta. If it is in the owner's premises, he must rent the place it is standing.

Suggestion: Abaye and Rava hold like Rebbi, unlike Chachamim (who say that Mesirah does not acquire in a Reshus ha'Rabim).

Rejection (Rav Ashi): Chachamim agree that Mesirah acquires if the seller said 'go make Chazakah and acquire.' They argue when he said 'go be Moshech and acquire'. Chachamim say that he is insistent that the buyer do Meshichah. Rebbi says, he merely suggests that he may acquire through Meshichah if he wants. He may also acquire through Mesirah.

86a (Mishnah): Metaltelim are acquired only through Meshichah.

(Rav Chisda): That applies only to something not normally lifted. What is normally lifted is acquired through Hagbahah, but not Meshichah.

Question (Rav Ada bar Masnah - Beraisa): If one stole a wallet on Shabbos, and he was dragging it out, he need not pay, for the liabilities for theft and Shabbos come at the same time. (Since he is liable to die, he need not pay.)

A wallet can be lifted, yet he acquires it through Meshichah!

Kidushin 25b (Rav): A large animal is acquired through Meshichah.

Question (Shmuel): The Mishnah says that it is acquired through Mesirah!

Answer: Rav holds like a different Tana.

Bava Metzia 8b (Idi): The word 'Mosirah' connotes that like one who is Moser (hands over) something to another person.

This applies to buying, but no one gives over Hefker!

Rishonim

Rambam (Hilchos Mechirah 4:3): Mesirah acquires only in a Reshus ha'Rabim, or in a Chatzer that does not belong to both of them. Meshichah acquires only in a Simta or in their joint Chatzer. Hagbahah acquires everywhere.

Rosh (5:2): The Rivam says that Mesirah is only when he gives the item from hand to hand. He learns from Bava Metzia 8b. It says that 'Mosirah' connotes handing over to another, therefore, it does not apply to Hefker. This is wrong. Holding it by the hoof is Mesirah, and the Gemara connotes that the seller did not hand it over! Also, all agree that Mesirah acquires if the seller said 'go make Chazakah and acquire', which connotes that it is not from hand to hand. Bava Metzia 8a means that when the seller said 'go make Chazakah' and the buyer holds it, it acquires, for the seller gave it to him to hold it on his command.

Rosh (5:4): Rebbi holds that a ship is acquired through Mesirah, and all the more so through Meshichah. We derive this from Chachamim, who say 'until he does Meshichah to exclude Mesirah. This implies that Rebbi holds that also Meshichah acquires. Also, we said that Rebbi holds that also Mesirah acquires a ship, i.e. in addition to Meshichah. Just like here, Mesirah does not exclude Meshichah, also everywhere it means Mesirah and all the more so Meshichah. This is clear from the Rashbam, who says that Mesirah acquires in Reshus ha'Rabim because Meshichah does not work there. Meshichah is taking to one's Reshus, and Reshus ha'Rabim is not his Reshus. Meshichah acquires in a Simta, for it is his Reshus to rest things there. Since Meshichah, an important Kinyan, can be done, Mesirah, an inferior Kinyan, does not acquire. Also, if some item could be acquired with Mesirah, but not Meshichah, Mesirah would acquire it in a Simta, for Meshichah does not acquire it! In Kidushin, Rav taught that a large animal is acquired through Meshichah. Shmuel challenged him from a Mishnah that says that Mesirah acquires it. We must say that the Mishnah means that even Mesirah acquires it, and Rav holds that only Meshichah acquires. We cannot say that Rav meant that even Meshichah acquires, and Shmuel asked from the Mishnah, which holds that only Mesirah acquires, for Shmuel himself explains a Mishnah (Bava Metzia 2a) to say that Meshichah acquires animals. R. Shimshon rejected these proofs. A Hefker animal is different, for Mesirah does not apply to it. The Halachah follows Chachamim, who say that he is insistent that the buyer do Meshichah. If he said 'go make Chazakah and acquire', all agree that he acquires through Mesirah.

R. Tam (brought in Rosh): Meshichah and Mesirah are not Mitzvos that Mevatel each other, i.e. only the best one works! Also, on 86a, we asked why Meshichah acquires something that can be lifted. Why didn't our Sugya ask this, if it also holds that Meshichah (an inferior Kinyan) does not acquire when Hagbahah (a better Kinyan) is possible?! Rav taught that Meshichah acquires a large animal. We challenged him from a Mishnah that says that Mesirah acquires. Why didn't we answer that the Mishnah discusses in a Reshus ha'Rabim, where Meshichah does not acquire? Mesirah is better, for it is given from hand to hand, in front of the seller. It acquires in a Reshus ha'Rabim, and all the more so in a Simta. The Mishnah teaches that only Mesirah acquires a large animal, but Meshichah does not. Meshichah works in the owner's absence, but Mesirah does not. This is not because Meshichah is better. Rather, 'Mesirah' connotes that it is in front of him.

Rebuttal (Rosh): Mesirah need not be from hand to hand, like I explained (above, 2). Mesirah works even in the seller's absence, e.g. when he says 'go make Chazakah and acquire.' I showed that a big animal is acquired also with Meshichah, unlike R. Tam. If Mesirah acquires in a Simta, what forced the Gemara to explain the Beraisa to mean 'it is not acquired until he does Meshichah from the Reshus ha'Rabim to a Simta'? We could say that both discuss a Simta, and they argue about whether the seller is particular about Meshichah, like we conclude! The Rashbam's Perush is primary. Also Rav Hai Gaon says that Meshichah is better than Mesirah. We find that Hagbahah is Mevatel other Kinyanim, which are inferior to it. In Kidushin, we did not answer that the Mishnah discusses in a Reshus ha'Rabim, and Rav discusses a Simta, because Mesirah connotes that also Meshichah acquires, but Meshichah connotes only Meshichah (so Rav should not have said 'Meshichah').

Tosfos (Bava Basra 76a DH Sefinah): The Ri says that Mesirah is weak, therefore, Meshichah is Mevatel it. Meshichah is strong, so Hagbahah is not Mevatel it.

Tosfos (Kidushin 25b DH Behemah): R. Chayim Kohen says that Mesirah does not work in a Simta because a Simta belongs to whoever was there first. Presumably, the seller was there first, and no Kinyan works in the seller's Reshus. Meshichah works only because the buyer takes it to his Reshus.

Poskim

Shulchan Aruch (CM 198:9): Mesirah acquires only in a Reshus ha'Rabim, or in a Chatzer that does not belong to both of them (Rema - and he brought the item there without permission of the owner of the Chatzer).

SMA (16): If he brought it there with permission, it is like the Reshus of the one who was authorized or of both of them.

Gra (13): Rashi (Bava Kama 48a DH Havya) says (regarding damages) that when one is allowed to enter a Chatzer, it is like his Chatzer.

Shulchan Aruch (ibid): Meshichah acquires only in a Simta or in their joint Chatzer. Hagbahah acquires everywhere.

SMA (17): Even though Meshichah acquires only with Mesirah (i.e. authorization to acquire), and Mesirah acquires in Reshus ha'Rabim, since he showed that he wants to acquire specifically with Meshichah, he acquires only through it.

Rema: If the seller said to acquire with Mesirah or Meshichah in a place where it does not acquire, the buyer does not acquire.

Gra (14): The Gemara said that (always,) Meshichah does not acquire in a Reshus ha'Rabim! Kidushin 25b asks how one can acquire an elephant according to R. Shimon, who requires Hagbahah. We do not say that he authorized him (to acquire with Mesirah or Meshichah)! This is unlike a stipulation to acquire land with money (which works), for letter of the law money acquires; the document is needed only because the buyer lacks resolve without it. If he says to acquire with money, he resolves without the document! This contradicts the Rema in Sa'if 5 (who said that a stipulation to acquire Metaltelim with money works. Nowadays, letter of the law money does not acquire!)