Yesterday, we saw the debate among the Rishonim as to whether one may count the omer during the period between sunset and nightfall – a period known as bein ha-shemashot. This period is treated in Halakha as one of uncertainty, when we cannot determine whether the halakhic day has ended and the halakhic night has begun. As it is uncertain during this period whether or not night has begun, and thus whether or not the time for counting the omer has arrived, some Rishonim maintained that one should not count the omer until tzeit ha-kokhavim (nightfall), when the obligation has assuredly set in. Others, however, ruled that since counting the omer nowadays constitutes a rabbinic obligation, commemorating the Biblical requirement which applied in the times of the Mikdash, we may be lenient in this regard, and count the omer during the uncertain period of bein ha-shemashot.
At the heart of this debate, as we saw, is the question as to the scope of the famous rule of “safeik de-rabbanan le-hakel” – that we may be lenient in situations of uncertainty when the law at stake is rabbinic in origin. This rule should, seemingly, allow us to rely on the possibility that halakhic night has already begun during bein ha-shemashot and thus permit counting the omer already at that point. Some poskim, however, maintain that the principle of “safeik de-rabbanan le-hakel” applies only “be-di’avad” – after the fact. In our case, this means that if somebody mistakenly counted the omer during bein ha-shemashot, then he may rely on the possibility that night had begun, such that he does not have to repeat the counting, since counting is required only mi-de’rabbanan. This is not to say, according to this opinion, that one may from the outset be lenient.
Another expression of this question arises in the context of tzitzit. The Shulchan Arukh (O.C. 10:7) addresses the case of a garment which is open from the bottom on both sides, but closed on top. Such a garment requires tzitzit only if the majority of the sides is open, but not if the majority is closed. In the case of a garment whose sides are precisely 50% open and 50% closed, it is uncertain whether the garment requires tzitzit, and one should therefore affix tzitzit, but should not recite a berakha when putting on the garment, given the uncertainty as to whether the berakha is warranted. The Shulchan Arukh adds that one may not wear this garment in a public domain on Shabbat, due to the possibility that it does not require tzitzit. Generally, one may wear a garment with tzitzit in a public domain on Shabbat only because the tzitzit are deemed part of the garment by virtue of the obligation to affix tzitzit to the garment. Otherwise, one would be considered “carrying” the tzitzit, in violation of Shabbat. Therefore, in a case where it is uncertain whether Halakha indeed requires affixing tzitzit, one may not wear the garment in a public domain, as it is possible that the tzitzit are not required, in which case wearing the garment in a public domain violates the prohibition against carrying in a public domain on Shabbat.
The later poskim debate the question of whether this ruling also applies to wearing such a garment in a karmelit – a public area that does not have the formal halakhic properties of a reshut ha-rabim (public domain). Carrying in a karmelit on Shabbat is forbidden only by force of rabbinic enactment, and therefore many poskim ruled that it is permissible to wear in a karmelit a garment whose status vis-à-vis tzitzit is uncertain. Since the prohibition at stake is a rabbinic provision, as opposed to a Torah law, the rule of “safeik de-rabbanan le-hakel” allows one to rely on the possibility that the garment truly requires tzitzit and thus may be worn in a public domain. This is the position of Chayei Adam (11, Nishmat Avraham 2) and the Mishna Berura (10:27). The Magen Avraham, however, forbade wearing such a garment even in a karmelit, asserting that the rule of “safeik de-rabbanan le-hakel” does not permit knowingly placing oneself in a situation of uncertainty. This debate seemingly parallels the aforementioned debate regarding the permissibility of relying on the rule of “safeik de-rabbanan le-hakel” from the outset to count the omer during the period of bein ha-shemashot.
It should be noted, as an aside, that the Chazon Ish (cited in Shemirat Shabbat Ka-hilkhatah, chapter 18, note 148) disputed the entire notion that one may not wear on Shabbat in a public domain a garment with an uncertain status regarding tzitzit. The Chazon Ish argued that once Halakha requires affixing tzitzit to the garment given the uncertainty involved, then the tzitzit are to be regarded as part of the garment, such that it is entirely permissible to wear the garment in a public domain on Shabbat.
(See also Rav Asher Weiss’ extensive article on this topic.)