1) "YE'USH" IN THE CASE OF A STOLEN OBJECT
QUESTION: The Gemara attempts to prove from a Beraisa that "Ye'ush she'Lo mi'Da'as" is Ye'ush. The Beraisa states that if a Ganav or Gazlan steals something from one person and gives it to another, the recipient may keep the object. The Gemara understands that this is because when something is stolen either through Geneivah or Gezeilah, the owner is assumed to have Ye'ush. The Gemara asks, if "Ye'ush she'Lo mi'Da'as" is not considered Ye'ush, then why may the recipient keep the object? The term "Ganav" refers to one who steals surreptitiously, so it is possible that the owner does not yet know that the object is missing. The Gemara answers that the term "Ganav" in the Beraisa does not have its usual connotation of one who steals surreptitiously, but rather it denotes a "Listim Mezuyan," an armed bandit.
The Gemara's initial proof is based on the Beraisa's assumption that in a normal case of Geneivah, the owner has Ye'ush. Why, then, does the Gemara cite a proof from a Beraisa, when it could cite proof from a Mishnah (Kelim 26:8, cited in Bava Kama 114a)? The Mishnah there teaches that according to the Chachamim, when a Ganav steals animal hides and decides to use them as cushions, his intent makes them fit to become Tamei. Although only the intent of the actual owner of an object can make it fit to become Tamei, the Ganav is considered the owner because in a normal case of theft, the true owner has Ye'ush. (RITVA in the name of "Yesh Makshim")
ANSWER: The RITVA answers that the Mishnah in Kelim might refer to animal hides which the owner already has discovered have been stolen. The Beraisa -- which states that the Ganav stole from one person and gave the object to another -- implies that the recipient received it immediately after the theft. In such a case, the owner probably has not yet had time to realize that the object was stolen. The Gemara chose the Beraisa over the Mishnah to cite as proof because the Beraisa more clearly discusses a case that is relevant to the issue of "Ye'ush she'Lo mi'Da'as."
2) SEPARATING FINE PRODUCE AS TERUMAH WITHOUT THE OWNER'S CONSENT
QUESTION: The Gemara attempts to prove from a Beraisa that "Ye'ush she'Lo mi'Da'as" is Ye'ush. The Beraisa discusses a person who separates Terumah from another person's grain without the knowledge of the owner of the grain. The Beraisa teaches that if the owner of the grain later comes and tells the person that he should have taken better fruit as Terumah, the separation of Terumah is valid because his statement shows retroactively that he consented to the separation of the Terumah. (TOSFOS and the Rishonim explain that although "Ye'ush she'Lo mi'Da'as" applies specifically when it can be assumed that the owner will have Ye'ush, in this case the owner's reaction can be predicted in advance. It is assumed that the owner will consent to the use of fine fruits for Terumah because of the Mitzvah involved.)
The Gemara rejects the proof and explains that the Beraisa is discussing a person who was appointed as a Shali'ach to separate Terumah but was not told by the owner which produce (the produce of higher quality or of lesser quality) to separate. The Beraisa teaches that if the Shali'ach separates good produce and the owner says that he should have separated better produce (and there is better produce), then the Terumah is valid. The Gemara adds that the case must be a case of a Shali'ach, because a verse teaches that only a Shali'ach may separate Terumah for someone else.
How does this answer refute the proof for Abaye's opinion? If a person must be appointed a Shali'ach in order to separate Terumah, and this Shali'ach was not told explicitly to separate the better produce as Terumah, then he should not be considered a Shali'ach to separate the better produce. Even if the owner later shows his consent to the better produce that was separated, it should be like "Ye'ush she'Lo mi'Da'as" since his consent was not given expressly at the time that the produce was separated as Terumah. (TORAS CHAIM)
ANSWER: The RITVA explains that this was, in fact, part of the Gemara's argument. The initial proof of the Gemara also understood that the person who separated the Terumah must have been a Shali'ach, since it is obvious that only a Shali'ach may separate Terumah for someone else. Nevertheless, the Gemara thought that this Beraisa supports Rava's opinion for the reason explained above: If the owner did not expressly appoint the Shali'ach to separate Terumah from the fine produce, then he cannot be considered a Shali'ach to do so. The Gemara's response, according to the Ritva, is that when a person appoints a Shali'ach, he is aware, at least, that the Shali'ach will do something on his behalf, even if he does not show clear consent for better produce to be separated. Since he is aware of the Shelichus, when he later consents to the separation of higher quality produce, that is assumed to have been his original intention as well when he appointed the Shali'ach. In the case of "Ye'ush she'Lo mi'Da'as," however, the owner has no knowledge whatsoever that he lost the object, and therefore his later Ye'ush cannot be understood to reflect his original intent. (The Toras Chaim gives a similar answer.)
3) "SIMAN HE'ASUY LI'DARES"
QUESTION: Rava rules that a "Siman he'Asuy li'Dares" -- a Siman that will likely be trampled and destroyed -- is considered a Siman. The Gemara concludes (end of 23a) that this is the Halachah.
How can this ruling be reconciled with the Gemara's ruling earlier on this page that "Ye'ush she'Lo mi'Da'as" is not Ye'ush? If a "Siman he'Asuy li'Dares" is considered a Siman, then the Halachah of "Ye'ush she'Lo mi'Da'as" should dictate that one is not permitted to take an object that he finds, even if it does not have a Siman, out of concern that it may have had a Siman originally and it lost its Siman when it was trampled. Rava maintains that an owner of a lost object does not expect his object to be trampled and its Siman to be lost, and thus the finder cannot assume that the owner had Ye'ush from his object as soon as it was lost (since it may have had a Siman at that time). Although the owner certainly will have Ye'ush when he finds out that the Siman was destroyed, Rava would rule that the finder cannot assume that the owner is already aware of his loss, and thus any object that is found without a Siman should automatically be considered a case of "Ye'ush she'Lo mi'Da'as." Consequently, a person should never be permitted to take an object that he finds that does not have a Siman. (KOS YESHU'OS)
ANSWER: The answer might be that both Rava and Rabah -- who disagree about the law in the case of a "Siman he'Asuy li'Dares" -- agree that even a "Siman he'Asuy li'Dares" is not usually trampled. Nevertheless, Rabah maintains that the owner has Ye'ush because there is a strong possibility that the Siman will be trampled, even if this happens only in a significant minority of cases. A person who finds an object with no Siman is entitled to keep it because of the principle of Rov; since most Simanim are not trampled and destroyed, the finder may assume that the object never had a Siman in the first place. Even though the Halachah in monetary matters normally does not follow the Rov, nevertheless with regard to an Aveidah, a lost object, the Halachah may be based on a Rov, since the object is not in anyone else's possession, as explained earlier (see Insights to 21:1). (M. KORNFELD)