Yesterday, we noted the theory posited by a number of Acharonim that the mitzva of sefirat ha-omer cannot be fulfilled with an uncertain counting. Meaning, if a person lost track of the days, and does not remember whether that day is, for example, the 20th or 21st day of the omer, he does not fulfill the obligation by counting both numbers, counting the 20th day and then counting the 21st day. Although he knows with certainty that one of his two counts is correct, nevertheless, he does not fulfill the mitzva, because counting, by definition, requires certainty. Since this person did not count either number definitively, he cannot be said to have truly counted that day.
However, as these writers themselves noted, this theory seems to be disproved by the famous comments of the Ba’al Ha-ma’or (end of Masekhet Pesachim) regarding the counting of the omer in the Diaspora. Communities in the Diaspora observe two days of Yom Tov to commemorate the observance of two days by ancient Diaspora communities who were unsure when the month began. As it took time to receive word of whether the new month was declared on the thirtieth or thirty-first day since the beginning of the previous month, these communities did not know on which day Yom Tov fell, and so they observed both days. In commemoration, Diaspora communities even today observe two days of Yom Tov. The Ba’al Ha-ma’or raised the question of why Diaspora communities do not also count each day of the omer twice, given the uncertainty in ancient times as to which day was the 16th of Nissan. Seemingly, just as Diaspora communities observe two days of Yom Tov, they should likewise conduct two counts each day of the omer in commemoration of the uncertainty that existed in the Diaspora in ancient times. The Ba’al Ha-ma’or answers that since the sefirat ha-omer obligation applies nowadays only as a commemoration, as the Biblical obligation is applicable (according to most opinions) only in the times of the Beit Ha-mikdash, there is no need to go so far as to require a double counting in the Diaspora. Secondly, he adds, such a practice would result in counting the final day of the omer on Shavuot, which would infringe upon the honor of Shavuot, which celebrates the completion of the omer period.
This entire discussion, of course, presumes the theoretical possibility of counting twice in situations of doubt to cover both possibilities. The Ba’al Ha-ma’or seems to have felt that an uncertain counting qualifies as a valid counting for sefirat ha-omer, in direct contrast to the theory noted earlier.
It has been suggested that a distinction may be drawn between the Ba’al Ha-ma’or’s discussion and the case of somebody who on a given day does not know which number to count. In the system proposed by the Ba’al Ha-ma’or, one has not lost track of the days, but rather does not know when the first day was to be counted. He therefore conducts two parallel counts, each day counting definitively twice, knowing with certainty which number day it is according to each count. Each time he counts on any given day, he knows with certainty that he counts the number subsequent to the number counted the previous day. Conceivably, we might accept this arrangement even if we disallow a person to count when he lost track of the days. In that case, the individual does not know with certainty each time he counts whether he is truly counting the number following the previous day’s counting, and thus such a counting is invalid. (See Ha-mitzvot Ba-parasha, Parashat Emor, 5776.)