KIDUSHIN 66 - Ari Kornfeld has generously sponsored the Dafyomi publications for this Daf for the benefit of Klal Yisrael.

1) ACCEPTING THE TESTIMONY OF A SINGLE WITNESS
QUESTION: Abaye lists three cases in which the testimony of a single witness ("Ed Echad") is accepted: when he testifies that "you ate Chelev," when he testifies that "your Taharos became Tamei," and when he testifies that "your ox was Nirva." The Gemara explains why Abaye needs to teach that a single witness is believed in each of these cases when one case would have sufficed (from which the other cases could have been derived).
RASHI (DH v'Tzericha) explains that in each case it is necessary to teach that the silence of the other person (the subject of the single witness' testimony, such as the person who ate Chelev, the person who owns the Taharos, or the person who owns the ox) is considered Hoda'ah (admission). One might have thought that Shetikah (silence) is judged as Hoda'ah only in certain circumstances. Abaye therefore teaches that Shetikah is considered Hoda'ah in all cases.
The words of the Gemara imply that the subject of the single witness' testimony is liable not due to the testimony of the witness but due to his own admission. Abaye, however, states that the single witness is believed. How is Abaye's statement to be reconciled with the words of the Gemara?
Moreover, the Gemara cites a dispute between Rava and Abaye. Abaye maintains that the testimony of a single witness is acceptable even for a "Davar sheb'Ervah"; a single witness may testify that a man's wife committed adultery. Rava argues and maintains "Ein Davar sheb'Ervah Pachos mi'Shenayim" (any matter which involves a prohibited relationship requires the testimony of two witnesses). If Abaye's reason for why a single witness is believed is the admission of the other party, what is Rava's argument? Abaye discusses the Hoda'ah of the defendant while Rava does not address the issue of Hoda'ah at all! Perhaps Abaye agrees with Rava that "Ein Davar sheb'Ervah Pachos mi'Shenayim" when the defendant's liability depends on the testimony of witnesses, but in a case of Hoda'ah no testimony at all is needed. Why does Rava argue with Abaye in this case, if testimony is not necessary?
ANSWERS: There is a fundamental dispute among the Rishonim as to when, and why, the testimony of a single witness is accepted. Below is a summary of the differing opinions, followed by an explanation of the Gemara according to each opinion.
RABEINU TAM concludes that the Gemara here teaches not that the testimony of a single witness is acceptable, but that the silence of the defendant is considered an admission to the claim against him ("Shetikah k'Hoda'ah").
The RITVA and most other Rishonim maintain that the Gemara is discussing the validity of the testimony of a single witness.
TOSFOS (DH Rava) and the RAN maintain that the two issues are interdependent. The testimony of the single witness and the Hoda'ah of the defendant work concomitantly.
The Gemara may be understood according to each of these opinions as follows.
(a) RABEINU TAM. Rabeinu Tam maintains that the subject of the Gemara's discussion is whether Shetikah is considered Hoda'ah. This is also implied by the "Tzerichusos" of the Gemara. However, a basic question may be asked. Why is the defendant's Hoda'ah needed when there is already testimony of the witness? Since a single witness is believed in cases of Isur, his testimony should suffice even without the defendant's Hoda'ah.
TOSFOS (65b, DH Nitme'u) cites the Gemara in Gitin (54b) which describes a case of a worker who testifies that his employer's food products became Tamei while he was working with them. The Gemara there teaches that a person is not always believed in such a situation. If he is presently working with the food, he is believed. If he has finished his work and has returned the food to the owner, he is not believed. The reason he is believed while he is still working with the food is that it is within his ability ("b'Yado") to make the food Tamei.
Based on the Gemara in Gitin, Rabeinu Tam concludes that the testimony of a single witness differs fundamentally from the testimony of two witnesses. When two witnesses testify, their word is accepted because of their inherent trustworthiness. In contrast, when the testimony of a single witness is accepted (in cases of Isur), it is not his inherent trustworthiness which gives credibility to his testimony. Rather, he is believed solely due to the logic of "b'Yado." Without "b'Yado," his testimony would not be accepted.
Rabeinu Tam explains that since there is no element of "b'Yado" in any of the cases mentioned by the Gemara here (it is not within the witness' ability to make the other person eat Chelev, to be Metamei the other person's Taharos, or to make the other person's ox a Nirva), it is necessary to rely on "Shetikah k'Hoda'ah" in order to substantiate the testimony of the single witness.
(b) RITVA. The Ritva explains that the subject of the Gemara is the trustworthiness of a single witness. According to the Ritva, two matters need clarification: the "Tzerichusos" of the Gemara (which imply that the Gemara is discussing "Shetikah k'Hoda'ah" and not the trustworthiness of a single witness), and the Gemara in Gitin mentioned above (which implies that without the logic of "b'Yado" the testimony of a single witness is not acceptable).
The Rishonim (see Ran) explain that the case of the Gemara in Gitin is unique and its law does not apply to the cases in the Gemara here. Since the worker's job is to ensure that the food is prepared properly and does not become spoiled or ruined, he has a Chazakah that he performed his job properly and that he did not let the food become Tamei. In order to accept his testimony that the food did become Tamei, the logic of "b'Yado" is necessary, because without "b'Yado" his testimony would be contradicted by the Chazakah.
The Gemara's "Tzerichusos" here do not mean that the testimony of the single witness is believed solely because of "Shetikah k'Hoda'ah." Rather, the Gemara is giving reasons for why Beis Din may assume that the defendant did not deny the witness' claim. Although the testimony of a single witness is accepted in cases of Isur, if the subject of his testimony denies what the witness says, the testimony of the witness is not accepted (because his testimony is contradicted by the word of another single witness, and they cancel each other out). One might have thought that the reason why the defendant does not respond to the claim of the witness is that he views the testimony as nonsense and not worth answering. Therefore, the Gemara must teach that his silence is viewed as Hoda'ah (or at least not as a denial of the witness' testimony).
(c) RAN. The Ran agrees with the view of most Rishonim that the testimony of a single witness is believed even without the logic of "b'Yado." However, the Ran explains the "Tzerichusos" of the Gemara in the same manner as Rabeinu Tam (they are expressing reasons for why one's Shetikah is like Hoda'ah) and he introduces a new understanding for why the testimony of a single witness is accepted.
The Ran points out that the Gemara's concept of "Shetikah k'Hoda'ah" applies only in cases of Isur. One's "Shetikah," silence, is not viewed as Hoda'ah in other types of cases, such as cases of monetary matters. The degree of Hoda'ah necessary to take money away from the defendant is not achieved by his mere silence in the face of a single witness' claim. Moreover, his lack of response to the claim cannot be considered a Hoda'ah even to create a situation of "Shavyei a'Nafshei" (wherein a person makes something forbidden to himself through his own explicit admission), which is a type of Hoda'as Ba'al Din in cases of Isur. The Hoda'ah by itself has no Halachic ramifications.
On the other hand, the single witness' testimony is also not sufficient by itself. The Ran proves this from the "Tzerichusos" of the Gemara, as mentioned above.
The Ran explains, therefore, that the Gemara here refers to a new, unique type of Hoda'as Ba'al Din. This new type of Hoda'ah does not operate through the mechanism of admission, but rather it enables the testimony of a single witness to be believed. Beis Din cannot accept the testimony of a single witness the same way it accepts the testimony of two witnesses. Rather, the testimony of a single witness needs additional support in order to have validity. It is the silence of the defendant which gives strength and credence to the single witness' claim. These two factors together -- the testimony of the single witness and the silence of the defendant -- give the single witness the necessary degree of trustworthiness.
Based on this explanation, the Ran clarifies the dispute between Rava and Abaye. Although Abaye maintains that the testimony of the witness is not accepted without the Hoda'ah of the defendant, it is not the Hoda'ah (Hoda'as Ba'al Din) which substantiates the witness' claim. Rather, the claim is substantiated through "Hoda'ah l'Ed Echad" -- "admission to the testimony of a single witness," a new form of credibility (Ne'emanus). Rava disagrees with Abaye and maintains that there is no such form of Ne'emanus. Had Abaye said that Beis Din may rely on the single witness alone, perhaps Rava would have agreed. However, since Abaye is discussing a case of "Davar sheb'Ervah," Rava rejects Abaye's new form of Ne'emanus and maintains that two witnesses are necessary.
(According to the approach of Rabeinu Tam, the dispute between Rava and Abaye still requires explanation.)

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