YEVAMOS 88 (4 Sivan) - Dedicated by Rabbi Kornfeld in memory of the members of his father's family who perished at the hands of the Nazi murderers in the Holocaust, Hashem Yikom Damam: His father's mother (Mirel bas Yakov Mordechai), brothers (Shraga Feivel, Aryeh Leib and Yisachar Dov sons of Mordechai), grandfather (Reb Yakov Mordechai ben Reb David Shpira) and aunt (Charne bas Yakov Mordechai, the wife of Reb Moshe Aryeh Cohen zt'l). Their Yahrzeit is observed on 4 Sivan.

QUESTION: The Mishnah (87b) discusses the case of a woman who receives word that her husband has died abroad. She marries another man, and then her first husband returns alive. The Gemara teaches that the Rabanan were lenient in such a case "Mishum Iguna"; they permitted the woman to remarry based on the testimony of a single witness. Because of that leniency, however, the Rabanan imposed a number of severe stringencies upon her in the event that her husband is found to be alive, as described in the Mishnah (87b). The purpose of these stringencies is to ensure that she will meticulously verify the testimony of that witness and determine beyond any doubt that her husband indeed is dead.
Why did the Rabanan permit her to remarry based on the testimony of a single witness, when, according to the Torah, she is an "Eshes Ish"? What authority do the Rabanan have to override the Isur d'Oraisa of "Eshes Ish"?
(The Gemara later (89a-90b) teaches that although the Rabanan have the authority to override Torah law through "Shev v'Al Ta'aseh," an enactment which passively overrides a Torah law, they do not have the power to uproot a Torah law actively, through "Kum va'Aseh." Allowing a woman to marry another man is an active violation of Torah law.)
(a) TOSFOS (DH Mitoch) explains that the Rabanan are empowered to "override," but not "uproot," a Torah prohibition (unless it is done through "Shev v'Al Ta'aseh," as the Gemara on 90b teaches).
The difference between "overriding" and "uprooting" an Isur d'Oraisa is as follows. To "uproot" an Isur means to do an act which everyone sees is contradictory to the Torah. In contrast, to "override" an Isur refers to an act which seems to have some logical (if not Scriptural) basis and does not appear to contradict anything in the Torah. In the case of the Gemara here, there are grounds ("Ketzas Ta'am u'Semach," as Tosfos writes) to assume that the woman's husband is dead, since a woman always investigates the matter before she marries another man. Hence, the Rabanan's allowance for her to remarry based on the testimony of a single witness is not considered an enactment that "uproots" the Torah's prohibition of "Eshes Ish," but rather one that "overrides" it.
According to Tosfos, the Gemara apparently accepts that this is one of the powers which the Torah grants to the Rabanan -- the authority to make enactments as they deem appropriate as long as they do not "uproot" a law written in the Torah. When their enactment is based on sound judgment and reason, it is not called "uprooting" Torah law. Since the Torah does not openly say not to accept such reasoning (and thus issuing such a ruling will not inadvertently lower the people's respect for the Torah or for the Rabanan), the Rabanan are empowered to institute any decree they deem necessary.
(b) RASHI in Shabbos (145b, cited by REBBI AKIVA EIGER in Gilyon ha'Shas) writes that in this situation the Rabanan uprooted the Kidushin retroactively ("Afke'inhu," a concept the Gemara discusses later on 90b) in order to permit the woman to remarry. Thus, retroactively she was never married to the first man.
The RITVA and Rishonim ask that if she was never married to the first man, her marriage to the second man is a full-fledged marriage mid'Oraisa. However, the Gemara (91a) clearly implies that the first marriage, and not the second, is considered the real one.
The Rishonim (ME'IRI and TESHUVOS HA'RASHBA 1:1162) answer that according to Rashi, the Rabanan uprooted the first Kidushin on condition that the husband does not return alive. Their retroactive annulment of the Kidushin does not take effect if he eventually returns. (The reason why the woman may remarry in the meantime, even though the possibility exists that her first husband will return alive, is that there is a Chazakah that since now he is not present, he will not return. See Tosfos to Gitin 33a, DH Afke'inhu.)
(c) The RITVA cites the RE'AH who explains that the testimony of the single witness is not accepted as "testimony" per se, but rather as a "Giluy Milsa b'Alma" that the woman no longer has a husband. The Torah does not always require formal testimony of two witnesses as evidence. In some situations, any clear, circumstantial proof ("Anan Sahadei" -- "we bear testimony") suffices. The Torah empowered the Rabanan to decide what proof is considered clear enough to permit a woman to remarry.
In the case of the Mishnah, the fact that a single witness testifies to the death of the husband is considered to be strong proof that the husband is dead, because a person would not lie in court about an indisputable fact which eventually will become known to all (through the return of the supposedly dead husband; the Gemara introduces this logic later on 93b). Additional proof is provided by the fact that a woman does not rely on the testimony of a single witness to remarry unless she has investigated the matter herself. Since the Rabanan decided that in this case there is sufficient circumstantial evidence of the death of her husband, the woman may remarry even mid'Oraisa. (See also TOSFOS YESHANIM.)
This might be the intention of the RAMBAM as well. In several places, the Rambam writes that the trustworthiness of a single witness is "mi'Divreihem" (that is, mid'Rabanan; see Hilchos Edus 5:2 and Hilchos Yibum 3:11). However, in the end of Hilchos Gerushin (13:29) the Rambam writes, "Do not wonder why the Rabanan permitted a most severe Ervah (Eshes Ish) to remarry based on the testimony of [a witness whose testimony the Torah normally does not accept, such as a single witness], because the Torah requires formal testimony of two witnesses and the other laws of testimony only for an event which can be known only through witnesses (for example, that one person killed another person, or that one person lent money to another person). In contrast, for a matter which eventually will become known on its own, the Torah does not require formal testimony, since it is very unlikely that a [normally invalid] witness would lie about such a matter." The Rambam concludes, "Therefore, the Rabanan were lenient in this matter and believed a single witness... in order that Jewish women should not remain Agunos."
The Rambam's words need clarification. He opens and concludes his comments by saying that the single witness is believed mid'Rabanan (as he writes in other places), but in the middle of his comment he says that the witness is believed mid'Oraisa.
The SHEV SHEMAITSA (7:11) explains that although the witness is believed mid'Oraisa as the Rambam says, the Rabanan usually were very stringent with Isurim as severe as "Eshes Ish" and they required two witnesses. In the case of a single witness who says that a woman's husband died, the Rabanan should have decreed that an "Eshes Ish" may not remarry based on such uncertain testimony, and they should have required two witnesses, mid'Rabanan. The reason why they did not require two witnesses in this case was the consideration to prevent women from becoming Agunos.
This is the intent of the Rambam when he writes that the Rabanan were lenient, while at the same time the witness is believed mid'Oraisa. This also explains why the Rambam writes in Hilchos Yibum that a single witness is believed only "Mishum Iguna." When the Rambam (in Hilchos Edus) writes that a single witness is believed "mi'Divreihem," he means that it is not explicitly written in the Torah that a single witness is believed in this case, but rather the Rabanan derived it from the verses. (The Rambam consistently refers to such Halachos mid'Oraisa as "mi'Divreihem.") The witness, however, is trusted mid'Oraisa. (The Rambam, unlike the Ritva, does not mention the logic that a woman thoroughly investigates the testimony of a witness, as the Gemara itself says, apparently because he understands (as the Gemara itself implies) that this logic is solely mid'Rabanan and does not affect the Halachah mid'Oraisa. The Ra'avad (ibid.) notes, like the Ritva, that this logic does serve to lend credence to the testimony of the single witness.)
(d) The RAMACH in his comments on the Rambam (end of Hilchos Gerushin) presents a different approach. He differentiates between the trustworthiness of a single witness (a Jewish male) whose testimony otherwise would be valid (i.e. if he would join with another valid witness) and that of a single witness whose testimony otherwise would not be valid witness (i.e. even if he would join with another witness, his testimony would not be valid). In the former case, the testimony is accepted to allow the woman to remarry mid'Oraisa (as the Ritva writes), while in the latter case, the witness is trusted only mid'Rabanan (as Tosfos writes). (See also Insights to Yevamos 92:1:a.)