Study Rosh Hashanah folio 23A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
Text Excerpt
למיטעי, אמרי: האי חסר הוא, והאי דלא עביד מאתמול, משום דלא אפשר. או דלמא מלא הוא, ובזמנו עבדו.
to err. They will be unsure how to interpret the lighting of the torches, as they will say: Perhaps this month is deficient, i.e., of 29 days, and the reason that the torch sequence was not performed yesterday, on Friday, is due to the fact that it was impossible to do so on Shabbat. Or perhaps it is a full, 30-day month, and they are performing the sequence at its proper time. Therefore, the rabbis instituted that the torches should be lit only after deficient months, and the absence of this signal means that the month was a full one.
וליעביד בין אמלא בין אחסר, וכי מקלע ראש חדש בערב שבת לא ליעביד כלל. וכיון דלא עבדינן מוצאי שבת ועבדינן אמלא — מידע ידעי דחסר הוא!
The Talmud suggests: And let them perform the ceremony both for a full, 30-day month and for a deficient one, and when Rosh Chodesh occurs on Friday, in which case they would have to light the torches after Shabbat, let them not perform it at all. And since the torches are not lit this month at the conclusion of Shabbat, and one normally performs the sequence for a full month, people will know that the month is deficient. In this manner, it should be possible to light the torches for all the months, with this one exception.
אפילו הכי אתו למיטעי, אמרי: האי מלא הוא, והאי דלא עבדי — איתנוסי הוא דאיתנוסי.
The Talmud answers: Even so, people might come to err, as they will say: This month is indeed full, and the reason that they are not performing the ceremony is that they were subject to circumstances beyond their control. Therefore, there might still be confusion as to the date of Rosh Chodesh that month.