1) IS A "KINYAN AGAV" EFFECTIVE FOR OWNERLESS PROPERTY?
OPINIONS: The Gemara cites a Beraisa (117b) which discusses the case of a person who steals a field, and afterwards a river overflows and floods the field. Rebbi Elazar rules that the thief is obligated to replace the stolen field with a field of equal quality. The Chachamim rule that the thief may say to the owner, "Here is your field," even though it was ruined by the flood. The TIFERES YISRAEL (#28) explains that according to the Chachamim, whose opinion is also that of the Tana of the Mishnah (117b), land always remains in the possession of the owner.
The Gemara (117b) cites another Beraisa in which Rebbi Elazar and the Chachamim argue in a similar case. A person stole a cow and an overflowing river drowned it. Rebbi Elazar rules that the thief must replace it with another cow. The Chachamim rule that the thief may claim, "Here is your cow." The Gemara inquires what the dispute is between Rebbi Elazar and the Chachamim in this case. (The Chachamim's position seems difficult, since, in this case, the cow is not land, and therefore the thief should be obligated to make restitution for it.)
Rav Papa answers that the case of the second Beraisa refers to a person who stole a field, and there was a cow lying in the field. The overflowing river flooded the field and drowned the cow. Rebbi Elazar and the Chachamim follow their respective positions that they express in the first Beraisa with regard to whether it is possible to steal land or not.
RASHI (118a, DH Parah) explains that the thief performed no act of Meshichah on the cow. Therefore, the cow has the same status as the land on which it lies. According to Rebbi Elazar who maintains that it is possible to steal a field, the thief acquires the cow along with the field. Therefore, the thief must pay for the lost cow because all movable objects on the field (such as the cow) are acquired through a Kinyan Agav with the field. According to the Chachamim, the thief acquires neither the field nor the cow on it.
Does this Gemara imply that a Kinyan Agav is effective for ownerless objects? That is, when a person acquires a field of Hefker, can he also acquire movable objects on the field through Kinyan Agav? Perhaps Agav works only when the owner of the field gives or sells the field to someone along with movable objects.
(a) The KETZOS HA'CHOSHEN (275:1) addresses this issue of whether or not one can effect a Kinyan Agav from Hefker. He proves from the Gemara here that a Kinyan Agav is effective even when the person does not acquire the land from someone else. Rashi implies that a Kinyan Agav would be effective to acquire objects from Hefker, since he explains that Rebbi Elazar understands that the cow is acquired with the field through Kinyan Agav even when the thief steals the field.
The Ketzos ha'Choshen explains further why Rashi understands that Rebbi Elazar must maintain that the cow is acquired through Kinyan Agav and not through Kinyan Chatzer. Kinyan Chatzer works only because the Chatzer is his domain, and thus whatever falls into his Chatzer becomes his. However, a thief does not actually own the Chatzer. His Kinyan on the stolen Chatzer makes it his property only with regard to liability for any unavoidable accidents that happen to it; he does not acquire objects situated in the Chatzer. Therefore, Rashi explains that according to Rebbi Elazar the thief acquires the cow through Kinyan Agav and not through Kinyan Chatzer. (The Ketzos ha'Choshen does not elaborate on the mechanism of Kinyan Agav. Apparently, he understands that one acquires movable objects through Kinyan Agav with any form of Kinyan he makes on the land, even if that Kinyan is a weak Kinyan (such as a Kinyan only for the purpose of making the thief liable for damage that happens to the land).)
(b) The NESIVOS HA'MISHPAT (202:2) disagrees with the Ketzos ha'Choshen. He maintains that one cannot acquire ownerless objects with a Kinyan Agav. A Kinyan Agav requires that there be another person who wants to transfer movable objects along with the land. (This is known as "Da'as Acheres Makneh" -- "the intention of another person effects the transaction," which applies to other cases of Kinyanim as well.) He points out that the Gemara in Kidushin (26a) derives the law of Kinyan Agav from the verse, "Their father gave them many gifts... with fortified cities in Yehudah" (Divrei ha'Yamim 2 21:3), which describes the gifts which Yehoshafat gave to his sons before he died. Since the verse refers to gifts of Metaltelin which Yehoshafat gave "Agav" the gifts of land (the cities in Yehudah), it implies that a Kinyan Agav is effective only when a person specifically gives the land and movable objects.
The Nesivos ha'Mishpat suggests that the reason why Rashi here implies that a thief's Kinyan Agav is effective is that Rebbi Elazar maintains that "Stam Gezeilah Ye'ush Be'alim." This means that we may assume that a victim of a theft despairs of ever retrieving the stolen property. (See the Gemara earlier (114a) which records a dispute between the Chachamim and Rebbi Shimon on this point.)
In a similar vein, TOSFOS (69a, DH Kol she'Liktu) writes that because of the owner had Ye'ush, it is considered as though he gave a gift to the thief. The Nesivos ha'Mishpat explains that since the owner has Ye'ush when his object is stolen, and thus it is considered as though he gave the object as a gift to the thief, it follows that theft indeed has an element of "Da'as Acheres Makneh." This is why a Kinyan Agav is effective in a case of theft. In contrast, a Kinyan Agav does not acquire an object of Hefker because there is no "Da'as Acheres Makneh" whatsoever. (See also DEVAR AVRAHAM (1:3:6) and CHAZON ISH, Bava Kama 16:13.) (D. Bloom)

118b----------------------------------------118b

2) BUYING ANIMAL PRODUCTS FROM SHEPHERDS
QUESTION: The Mishnah states that one may not buy wool, milk, or goats from shepherds. RASHI (DH Ein) explains that the reason is that a shepherd is suspected of having stolen such items from the flock which he is employed to watch. The Gemara cites a Beraisa which states that one may buy ready-made clothing from them, because such items certainly belong to the shepherds. The Beraisa adds that one may buy milk and cheese from shepherds in the desert, but not in settled areas.
RASHI (DH Tefurim) explains that the reason why one may buy ready-made clothing is that even if the material from which the clothing is made in fact is stolen, nevertheless the shepherds acquired it with a Shinuy when it was made into a garment. (See RASHBA who disagrees with Rashi, and see BACH (CM 358:2) who answers the Rashba's question on Rashi.)
Rashi (DH Chalav) also explains why one may buy milk and cheese from shepherds in the desert. The owners of the animals usually do not go to the desert to take the materials produced by their animals (because going there involves too much effort for too little gain), and thus they allow the shepherds to keep the materials. (See TUR CM 358.) In contrast, in settled areas it is the common practice for the shepherds to bring the milk and other products to the owners (Rashi DH Aval), and therefore the products do not belong to the shepherds.
What is the difference between ready-made clothing and cheese in a settled area? Just as one may buy clothing from the shepherds because even if the material is stolen, they acquired it with a Shinuy, one should also be permitted to buy cheese, even in town, because even if the milk is stolen, when the shepherds make cheese from the milk they acquire it through a Shinuy.
ANSWERS:
(a) The PNEI YEHOSHUA explains that one may not purchase l'Chatchilah an item when there is strong reason (a Chazakah) to assume that it is stolen, even if the thief acquired it with a Shinuy. Purchasing such an item constitutes "Mesayei'a Ovrei Aveirah," assisting transgressors. If no one would buy stolen goods from a thief, the thief stop stealing. Accordingly, buying from him is prohibited since it supports and encourages his thievery. (The Pnei Yehoshua writes that this is the ruling of the SHULCHAN ARUCH CM 358:1; see also CM 269:1 and S'MA #1.)
In contrast, one is permitted to purchase ready-made garments from the shepherds because there is no certainty that the wool from which the garments are made was stolen. Perhaps they bought the wool to make clothes in the same way that tailors do. Since there is only a doubt that the wool might be stolen, one may buy the garments. In contrast, it is unusual for shepherds to buy milk in order to produce cheese, and thus one must assume that the cheese they sell is made from stolen milk and if he purchases the cheese he will be encouraging theft.
(b) RAV YEHOSHUA LEIB DISKIN (in TORAS HA'OHEL page 16a, DH Sham) answers that the Gemara must be referring to the purchase of cheese outside of Eretz Yisrael. The Mishnah earlier (79b) states that one may not raise Behemah Dakah (small, domesticated animals, such as a sheep and goats) in Eretz Yisrael.
The RAMBAM (Hilchos Ma'achalos Asuros 11:25) writes that in Chutz la'Aretz one may buy cheese only from a seller who has a Chezkas Kashrus (he is known to be reliable). Since the shepherds are known to be thieves they clearly cannot be relied upon for Kashrus, and one must suspect that they may have made the cheese with non-kosher materials.
(The Rambam's reasoning seems to contradict the words of TOSFOS in Chulin (12a, DH Harei), who writes that when one is suspected of stealing he is not automatically suspect of improperly slaughtering an animal. Perhaps, however, Tosfos agrees that a higher level of reliability is required for a person to have a Chezkas Kashrus and to trust him with regard to purchasing cheese from him in Chutz la'Aretz.) (D. Bloom)