Now that we have presented the background to the position of Rabbeinu Tam regarding two shkiyas, and the opposing position of the GR”A, the question remains whether the visible, “first,” shkiya has any halakhic significance for Rabbeinu Tam. Here is where the Tosafot from the daf comes up. Tosafot on 20b, s.v. nifsal, drawing on Rabbeinu Tam’s Sefer HaYashar, states that it does. Tosafot is bothered why a special verse (biyom hakrivo et zivcho) is needed to invalidate blood of a korban that is not placed on the altar on the same day that the animal is slaughtered since we already know that all the avodot, sacrificial rites, must be done during the day. Tosafot’s answer is that this extra verse tells us that the blood of a sacrifice becomes invalid even after the first shkiya.
The way to know, says Rabbeinu Tam, is based on the phrasing that is used. Tosafot points out that when the Gemara states that blood becomes invalid at sunset, it uses the phrase bi’shkiyat ha’chama, at the setting of the sun. This phrase, says Rabbeinu Tam, means the beginning of the setting, i.e., the first shkiya. It is only when the Gemara uses the phrase mi’she’tishka ha’chama, when the sun has set, that it is referring to the second setting. Making this distinction between the two phrases allows Rabbeinu Tam to state that the Gemara in Shabbat (35a) that placed tzeit at 3/4 of a mil after shkiya was talking about the second shkiya, because it used the phrase mi’she’tishka. In contrast, the Gemara in Pesachim (93a) that gave the period of 4 mil was talking from the first shkiya because it used the phrase mi’shkiyat ha’chama.
It is interesting to consider the significance of this first shkiya within the approach of Rabbeinu Tam. It seems, for Rabbeinu Tam, that the end of the day has 3 stages. First there is physical sunset. This is an ongoing process, which starts with shkiyat hachama, the setting of the sun, and ends with mi’she’tishka ha’chama, once it has finally set. This is a period which is technically day, but seen as leading into night. This roughly corresponds to the period that we call twighlight (which comes after sunset), where there is still some direct sunlight lighting the sky. Then comes the period which is the onset of night, but not fully night proper – this period is bein ha’shemashot, beginning at the “second shekiya”and roughly corresponds to what we call dusk. And finally there is night proper, tzeit hakokhavim.
Dusk, bein heshemashot, which is the beginning of night, but not night proper, has the status of “doubtful day, doubtful night.” As Rav Soloveitchik explained, in his article Yom VaLaila, “Day and Night,” in Shiurim liZekher Aba Mari, Yahrtzeit Lectures in Memory of My Father, vol. 1
פירושו של ספק אינו מציין פקפוק בדעת חז”ל, שלא יכלו להכריע אם זמן זה בכלל יום או בכלל לילה, כי הלא מקרא מלא הוא מעלות השחר ועד צאת הכוכבים, ושיעור יום ודאי נאמר כאן. אלא שבזמן זה ישנה חלות יום וגם חלות לילה. שניות נאמרה בו, הוא גם יום והוא גם לילה, והכל תלוי מאיזה בחינה נסתכל בו… שני החלותים הסותרים זה את זה מחדשים שזמן זה ספק המבטא במובן זה עימות והתמודדות של יום ולילה
The explanation of this “doubtful status” does not indicate that there Chazal had an uncertainty as to the facts, that they could not come to a conclusion whether this period was included in “day” or in “night.” For behold, it is an explicit verse, “From the morning star until the emerging of the stars,” and certainly this is the definition of day. Rather, at this time [of bein hashemashot] there is a dual status – of day and of night. A duality is being stated here – this period is both day and night, and it all depends on the perspective with which you look at it… These two statuses, which contradict one another, create a new reality that this time period is a “doubt,” which is a way of expressing this tension between day and night.
Rav Soloveitchik explains the competing definitions to be a definition based on light and darkness, as opposed to a definition based on sunrise and sunset. For our purposes, we can look at it as different degrees of the light-darkness mix. The period after the first shkiya, still has direct sunlight (although no visible sun), and is day. The period after the “second shkiya,” is genuinely getting dark, but not fully dark, so it has this ambiguous status, which is defined halakhically as safek.
For Rabbeinu Tam there is a nice parallel here to the period between amud hashachar and sunrise. The mishna in Megilah (20a) states that all day mitzvot are valid from sunrise on, but if they were performed starting at amud ha’shachar one fulfills his obligation. The standard explanation of this, and this is how Rashi explains it, is that day starts fully at amud ha’shachar but because it is not so obvious when that is, the Rabbis wanted people to wait until sunrise, lest they err. Rav Soloveitchik explains this otherwise. He states that this period corresponds to bein hashemashot, as it has elements of both light and darkness. However, as opposed to bein hashemashot where this tension expresses itself halakhically in the form of safek, here it expresses itself halakhically in the form of lichatchila and bi’di’eved. As a base position, lichatchila, this time between the morning start and sunrise is not yet day, because the sun has not risen and it is not fully light. However, bi’dieved, if one did a day mitzvah during this period, it will count as day, because it does have day elements to it.
Now, according to Rav Soloveitchik, it is strange that the counterpart to this 72 minute period in the beginning of the day is a mere 13.5 minute period at the end of the day. It is also strange that in one case we treat the tension of day-night as a doubt, and in the other case as a lichatchila/bi’di’eved. However, according to Rabbeinu Tam this works out quite well. Just as 72 minutes before sunrise counts as day (maybe – contra Rav Soloveichik – even li’chatchila on a d’orraita level), so the first 58.5 minutes after sunset counts as day. It is only the last 13.5 that has no parallel in the morning and is treated as a doubt. The reason these “mixed times” – 72 minutes after the morning star, and 58.5 minutes after sunset – are treated as day rather than night, is because at the human level we respond to the presence of light and focus on it. Once some light enters the sky in the morning, we feel that daytime has come. And as long as there is still some sunlight in the sky, we cling on to the day, and feel that it has not yet gone. “My soul is to God like the watchers for the dawn, the watchers for the dawn.” Only when all the sunlight has escaped, but it is not completely dark, are we willing to acknowledge the partial onset of night.
So, to return to the period after the first sunset – we now see that it already has a mix of light and dark, that it has elements of the night, but they are not yet dominant. Thus, it is still technically day, but it is beginning to feel “night-ish”. This is why, according to Rabbeinu Tam, the extra verse by sacrifices can teach that the blood of sacrifices is invalidated at the first sunset. For this case, we will focus on the night element, and we will see this time as already night. [This is somewhat parallel to Rav Soloveitchik’s lichatchila of treating the post-amud hashachar period as still night]. Perhaps we can even be more precise than that. The verse that Tosafot was referring to does not teach that the blood becomes invalid at night, but rather “on the day that you slaughter you must apply the blood.” That is, it must be the same day as the slaughtering. Since this period now has night elements, even if it is not night proper, we cannot say that it is truly the same period – the same day – in which the animal was slaughtered.
This point brought out even clearer in the position of Ramban in Torat Ha’Adam (source 1, in Primary Sources – 2), which Shulkhan Arukh (source 2) follows. Ramban asks – when Chazal tell us that there is a mitzvah of tosefet Shabbat or tosefet Yom HaKippurim, to add to Shabbat or Yom Kippur from the day before, starting when can one begin this period of addition? He proceeds to present and analyze, and agree with, Rabbeinu Tam’s position on tzeit, bein hashemashot, and two shkiyas, and after much analysis concludes that the period of addition can begin at the first shkiya. He then points out that this time is roughly equivalent to the period of plag hamincha which is 1 1/4 hours before the end of the day, which he assumes means before tzeit. Thus, 1 1/4 hours = 75 minutes before tzeit, which is only 3 minutes earlier than sunset for Rabbeinu Tam. As we know, plag hamincha is the time when one can daven aravit, and can even make havdalah on Shabbat (without a candle, of course, and this does not allow melacha, it just means you fulfill your obligation of havdalah!). So, says Ramban, this is a time that can already be associated with the next day, so this is the time during which one can make a tosefet Shabbat. Earlier than plag/sunset would be meaningless, but any time after this would be a meaningful addition to the following day.
Thus, for Ramban, sunset and plag effectively coincide. And because the sun has already set, and the day is starting to darken, it is a time that can be – like in the case of the blood of korbanot – connected to the nightime, or the next day, and thus can be used for davening ma’ariv or for making it into tosefet Shabbat.
Ramban takes this idea one step further, however. How, he asks, can one make a tosefet for Tisha b’Av, if the Torah never indicated that such a tosefet could be made. We could restate the question as follows: If the idea of tosefet is that one is bringing in kedusha of Shabbat into Friday afternoon, then how can this be applied to a day like Tisha b’Av which has no kedusha? To this Ramban answers as follows:
שהקבלה אוסרת עליו בזמן הזה שהוא משקיעת החמה והוא מפלג המנחה ולמעלה, הואיל והוא יכול לעשותו תוספת לימים של תורה יכול לעשותו נמי תוספת ליום של דבריהם הואיל ורצה להוסיף אותו עליו ולעשותו כיום עצמו
For the accepting [of this period as the beginning of Tisha b’Av] makes it forbidden to him during this time, which is from sunset, which is plag hamincha, and later, since he can make it an addition for the Torah days, he can also make it an addition for a Rabbinic day, because since he wants to add onto the day and make it like the day itself, [he is able to do so].
That is, according to Ramban, since this period begins at sunset, what a person is doing with creating a tosefet is not introducing kedushat Shabbat into Friday, but rather designating this time as actually nightime, as Saturday itself! Just like the verse considered it already night for the blood of sacrifices, a person can subjectively consider it night because of its night elements. Thus, it can be done even without any kedusha. It can be done on Tisha b’Av, just as a person can daven ma’ariv on a Wednesday after plag hamincha.
Ramban leaves this possibility saying “vi’zo shita t’luya“ – this is a speculative possibility. And, indeed, although this is a very logical and attractive position within Rabbeinu Tam’s universe, it requires one to adopt a very specific understanding of tosefet yom, one that we normally do not adopt in other halakhic areas. Thus, even if one has already accepted upon herself tosefet Shabbat, we would still consider it to be Friday day for other halakhot (hefsek tahara, a baby being born, etc.). However, it is quite possible that this is because we rule that bein hashemashot begins at sunset, and that the period of tosefet starts earlier. So while for Ramban and Rabbeinu Tam this tosefet period, occurring after sunset, could be one of designating the time as night, for us, where it occurs before sunset, it can at most be one of introducing the sanctity of the next day into the current one.