The Torah in Parashat Naso introduces the law of sota, which addresses the situation of a man who suspects his wife of an adulterous affair. If a husband warns his wife not to be secluded with a certain man, and the woman is seen violating the warning and going into a secluded room with that individual, she and her husband may not engage in marital relations until she undergoes the process outlined here in the Torah. This process entails her drinking special waters, and if she survives, then she is considered innocent and may resume normal relations with her husband.
The Talmud Yerushalmi (Sota 1:2) raises the question of whether these laws apply in the case of a husband who warns his wife not to go into seclusion with an immediate family member, such as her father or brother. According to one view, violating this warning does not render the woman a sota, and she and her husband may continue living together as husband and wife. The classic commentators to the Yerushalmi (Korban Ha-eida and Penei Moshe) explain that the Yerushalmi’s question is whether the laws of sota hinge upon the prohibition of yichud – secluding oneself with a member of the opposite gender other than one’s spouse. According to the aforementioned view, the concept of sota is applicable only if the suspected adulterer is somebody with whom the wife is halakhically forbidden to be secluded. If she secludes herself with somebody with whom seclusion is halakhically permissible, such as her father, then even though her husband had warned her not to seclude herself with that person, the laws of sota do not apply.
Interestingly enough, this issue may have important practical halakhic implications. The Gemara in Masekhet Sota (26b) cites Shemuel’s comment that the laws of sota apply even if the man with whom the husband forbids seclusion is shachuf (impotent). Although it may be presumed in such a case that no adulterous act occurred, nevertheless, the laws of sota apply. The Gemara, somewhat surprisingly, reacts to Shemuel’s comment by asking, “Peshita” – why such a self-evident halakha needed to be stated. In the Gemara’s eyes, it is obvious that the laws of sota apply irrespective of the suspected adulterer’s sexual capabilities. The Gemara answers that Shemuel’s ruling was necessary because the Torah introduces the laws of sota by describing the scenario of a suspected adulterous relationship that included semenal ejaculation (“shikhvat zera” – Bamidbar 5:13). For our purposes, however, it is significant that the Gemara initially found Shemuel’s ruling intuitive and self-evident. As noted by Rav Moshe Yehuda Leib Zilberberg, in his Zayit Ra’anan (E.H. 1:1), this would seem to prove that the prohibition of yichud forbids even an impotent man from secluding himself with a female. After all, if yichud in such a case would be permissible, then the status of a shachuf with respect to the laws of sota would hinge on the aforementioned debate in the Yerushalmi. According to the view that a wife does not become a sota by being secluded with a family member, this would be true also in the case of a shachuf. As such, Shemuel’s ruling would hardly be obvious. Evidently, Rav Zilberberg reasons, the Gemara worked off the assumption that yichud is forbidden even for an impotent man who is incapable of intercourse, and therefore Shemuel’s halakha initially seemed self-evident.
Rav Eliezer Waldenberg, in a letter to Rav Yosef Shalom Elyashiv which he then published in his Tzitz Eliezer (7:46), disagreed. Among his refutations of Rav Zilberberg’s proof is the fact that the question raised by the Yerushalmi is never mentioned in the Talmud Bavli. Indeed, the Mishna (Sota 24a) makes a generic statement that the laws of sota apply to all relatives with whom intimacy is forbidden (“Al yedei kol ha-arayot maknin”), which would certainly suggest that they apply even in the case of immediate family members. Quite possibly, then, the Bavli assumed that the laws of sota do not hinge at all on the prohibition of yichud, and they apply even if the man in question is somebody with whom the wife is halakhically permitted to be secluded. As such, even if yichud is permissible for an impotent man, the Gemara justifiably found Shemuel’s ruling obvious. Indeed, Rav Waldenberg rules that an elderly, impotent man who is incapable of intercourse may be secluded with a woman (see Tzitz Eliezer, vol. 6, pp. 230-231).