Today's Daf Yomi
April 9, 2020 | ט״ו בניסן תש״פ
Masechet Shabbat is sponsored in memory of Elliot Freilich, Eliyahu Daniel ben Bar Tzion David Halevi z"l by a group of women from Kehilath Jeshurun, Manhattan.
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This month's learning is sponsored by Leah Goldford in loving memory of her grandmothers, Tzipporah bat Yechezkiel, Rivka Yoda Bat Dovide Tzvi, Bracha Bayla bat Beryl, her father-in-law, Chaim Gershon ben Tzvi Aryeh, her mother, Devorah Rivkah bat Tuvia Hacohen, her cousins, Avrum Baer ben Mordechai, and Sharon bat Yaakov.
Shabbat 34
The mishna recommends that a husband should ask his wife before Shabbat starts if she tithed the produce and set up an eiruv and if so, she should light the candles. What things cannot be done once the time of twilight (bein hashmashot) has arrived? What things can still be done during this time period? The gemara resolves a potential contradiction in the mishna reagarding eiruv. What is hatmana? What type is forbidden even before Shabbat and what type is permitted even during twilight. Why? Twilight is considered a time that is maybe day, maybe night or maybe both. What is the tannatic debate regarding when exactly is twilight? What is the relevance for this time of doubt regarding impurity of a zav? Raba and Rav Yosef have a disagreement about how to understand the time of twilight according to Rabbi Yehuda, as his words seem to include contradictory statements and each resolves it in a different way. This disagreement is consistent with their opinion regarding the length of time that twilight spans.
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תוכן זה תורגם גם ל: עברית
ואית להו צערא לכהנים לאקופי אמר איכא איניש דידע דאיתחזק הכא טהרה אמר ליה ההוא סבא כאן קיצץ בן זכאי תורמסי תרומה עבד איהו נמי הכי כל היכא דהוה קשי טהריה וכל היכא דהוה רפי צייניה
and the priests are troubled by being forced to circumvent it, as it is prohibited for them to become ritually impure from contact with a corpse. There was suspicion, but no certainty, that a corpse was buried there. Therefore, they were unable to definitively determine its status. Rabbi Shimon said: Is there a person who knows that there was a presumption of ritual purity here? Is there anyone who remembers a time when this place was not considered ritually impure, or that at least part of it was considered to be ritually pure? An Elder said to him: Here ben Zakkai planted and cut the teruma of lupines. In this marketplace Rabbi Yoḥanan ben Zakkai, who himself was a priest, once planted lupines that were given to him as teruma. On that basis, the conclusion can be drawn that it was definitely ritually pure. Rabbi Shimon, like Jacob, also did so and took steps to improve the city and examined the ground (Tosafot). Everywhere that the ground was hard, he pronounced it ritually pure as there was certainly no corpse there, and every place that the ground was soft, he marked it indicating that perhaps a corpse was buried there. In that way, he purified the marketplace so that even priests could walk through it.
אמר ההוא סבא טיהר בן יוחי בית הקברות אמר ליה אילמלי (לא) היית עמנו ואפילו היית עמנו ולא נמנית עמנו יפה אתה אומר עכשיו שהיית עמנו ונמנית עמנו יאמרו זונות מפרכסות זו את זו תלמידי חכמים לא כל שכן יהב ביה עיניה ונח נפשיה נפק לשוקא חזייה ליהודה בן גרים אמר עדיין יש לזה בעולם נתן בו עיניו ועשהו גל של עצמות:
A certain Elder said in ridicule and surprise: Ben Yoḥai purified the cemetery. Rabbi Shimon got angry and said to him: Had you not been with us, and even had you been with us and were not counted with us in rendering this ruling, what you say is fine. You could have said that you were unaware of my intention or that you did not agree or participate in this decision. Now that you were with us and were counted with us in rendering this ruling, you will cause people to say that Sages are unwilling to cooperate with one another. They will say: If competing prostitutes still apply makeup to each other to help one another look beautiful, all the more so that Torah scholars should cooperate with each other. He directed his eyes toward him and the Elder died. Rabbi Shimon went out to the marketplace and he saw Yehuda, son of converts, who was the cause of this entire incident. Rabbi Shimon, said: This one still has a place in the world? He directed his eyes toward him and turned him into a pile of bones.
מתני׳ שלשה דברים צריך אדם לומר בתוך ביתו ערב שבת עם חשכה עשרתם ערבתם הדליקו את הנר ספק חשכה ספק אינו חשכה אין מעשרין את הודאי ואין מטבילין את הכלים ואין מדליקין את הנרות אבל מעשרין את הדמאי ומערבין וטומנין את החמין:
MISHNA: There are three things a person must say in his home on Shabbat eve at nightfall and not before. The mishna elaborates: He should ask the members of his household, have you tithed the crop that required tithing? Have you placed the eiruv for joining the courtyards and joining the Shabbat borders? If you have done so, light the lamp in honor of Shabbat. The Sages stated a principle: If the time arrives on Friday when there is uncertainty whether it is nightfall and uncertainty whether it is not yet nightfall, one may not tithe the crop that has definitely not been tithed, and one may not immerse ritually impure vessels in a ritual bath to render them ritually pure, and one may not light the Shabbat lights. However, one may tithe demai, doubtfully tithed produce, which must be tithed due to mere suspicion. And one may place an eiruv and insulate the hot water to be used on Shabbat.
גמ׳ מנא הני מילי אמר רבי יהושע בן לוי אמר קרא וידעת כי שלום אהלך ופקדת נוך ולא תחטא אמר רבה בר רב הונא אף על גב דאמור רבנן שלשה דברים צריך אדם לומר וכו׳ צריך למימרינהו בניחותא כי היכי דליקבלינהו מיניה אמר רב אשי אנא לא שמיע לי הא דרבה בר רב הונא וקיימתי מסברא
GEMARA: The Gemara attempts to clarify: From where are these matters, that one must ask these questions in his home at nightfall of Shabbat, derived? Rabbi Yehoshua ben Levi said: As the verse said: “And you shall know that your tent is in peace; and you shall visit your habitation, and shall not sin” (Job 5:24). From here it is derived that one should visit his habitation, i.e., ask in his home, so that he will not come to sin. Rabba bar Rav Huna said: Although the Sages said that there are three things a person should, indeed he is required to, say in his home on Shabbat eve at nightfall, one must say them calmly so that the members of his household will accept them from him. If he says them harshly, his family members may mislead him and cause him to sin. Rav Ashi said: I did not hear this halakha of Rabba bar Rav Huna, but I fulfilled it based on my own reasoning.
הא גופא קשיא אמרת שלשה דברים צריך אדם לומר בתוך ביתו ערב שבת עם חשכה עם חשכה אין ספק חשכה ספק אינו חשכה לא והדר תני ספק חשכה ספק אינו חשכה מערב:
The Gemara asks: This mishna itself is difficult, as it contains an internal contradiction. On the one hand, you stated initially that there are three things a person must say in his home before Shabbat at nightfall, and this means: At nightfall, i.e., before nightfall, yes, he should say those things; when there is uncertainty whether it is nightfall and uncertainty whether it is not yet nightfall, no, he should not say them. Even if one were to ask then, it is no longer permitted to correct these matters. And then it taught: When there is uncertainty whether it is nightfall and uncertainty whether it is not yet nightfall, one may place an eiruv. One may correct the situation even then. Why did the mishna restrict asking these questions to an earlier time?
סימן בגופיא זימרא ציפרא בחבלא דמילתא:
Incidentally, prior to answering this question, the Gemara lists all of the other halakhot in tractate Shabbat stated by the Sage who answers the question, with the mnemonic: Self, pruning, bird, cord, silk.
אמר רבי אבא אמר רב חייא בר אשי אמר רב לא קשיא כאן בעירובי תחומין כאן בעירובי חצרות
Rabbi Abba said that Rabbi Ḥiyya bar Ashi said that Rav said: This is not difficult and there is no contradiction here. Here, at the beginning of the mishna, where it indicates that the eiruv can only be placed while it is still day, it is referring to the joining of Shabbat boundaries, which is based on a Torah law. Therefore, one must place this eiruv while it is definitely day. And here, where the mishna said that it is permitted even when it is uncertain whether or not it is already nighttime, it is referring to the joining of courtyards, which is more lenient and based merely on a stringency.
ואמר רבא אמרו לו שנים צא וערב עלינו לאחד עירב עליו מבעוד יום ולאחד עירב עליו בין השמשות זה שעירב עליו מבעוד יום נאכל עירובו בין השמשות וזה שעירב עליו בין השמשות נאכל עירובו משחשכה שניהם קנה עירוב
In connection to this, the Gemara cites the halakha that Rava said in order to emphasize the rabbinic aspect of the halakhot of eiruv: One to whom two people said: Go and place an eiruv, a joining of courtyards (Rabbeinu Ḥananel), for us. For one of them he placed an eiruv while it was still day, and for one he placed an eiruv at twilight, when it is uncertain whether it is day or night. The one for whom he placed an eiruv while it was still day had his eiruv eaten during twilight, and the one for whom he placed an eiruv during twilight had his eiruv eaten after nightfall. The principle is as follows: Whether or not an eiruv takes effect is determined at the moment that Shabbat begins. If one placed the eiruv beforehand, and it remains intact at the moment Shabbat begins, the eiruv is in effect. However, if the eiruv that was placed at the appropriate time was eaten during twilight, it is problematic. Twilight is a period of uncertainty. There is uncertainty whether it is day, and consequently the eiruv was not in place at the moment that Shabbat began, or whether it is night, and it was in place. In the latter case, there is still uncertainty as to whether or not the eiruv was in place prior to Shabbat, so that it could take effect at all. In that case, Rava ruled that both of them acquired the eiruv.
מה נפשך אי בין השמשות יממא הוא בתרא ליקני קמא לא ליקני ואי בין השמשות ליליא הוא קמא ליקני בתרא לא ליקני בין השמשות ספקא הוא וספקא דרבנן לקולא:
The Gemara is surprised by this: Whichever way you look at it, this ruling is difficult. If the twilight period is considered day, let the latter one acquire his eiruv, but let the first one not acquire his because his eiruv was eaten while it was still day. And if the twilight period is night, let the first one acquire his eiruv, but let the latter one not acquire his eiruv because his was not placed before Shabbat. In any event, it is impossible for the eiruv in both of these cases to be valid. The Gemara answers this according to Rava’s position: The status of twilight is uncertain, as it is unknown whether it is day, or night, or both, and uncertainty in the case of a rabbinic ordinance is ruled leniently. Therefore, in both cases the eiruv is acquired.
(ואמר) רבא מפני מה אמרו אין טומנין בדבר שאינו מוסיף הבל משחשכה גזרה שמא ירתיח אמר ליה אביי אי הכי בין השמשות נמי ניגזר אמר ליה סתם קדירות רותחות הן
And Rava said: Why did they say that one may not insulate hot water even in something that does not add heat, but only retains the pre-existing heat, from nightfall on Friday? It is a decree lest one come to boil the pot on Shabbat. Abaye said to him: If so, if it is due to concern that one may boil it, then during twilight we should also issue a decree and prohibit insulating in something that does not add heat. Rava said to him: During twilight, there is no reason to be concerned because at that time most pots are boiling, as they have just been taken off of the fire. Later at night the pots cool down and it is conceivable that one may come to boil them in order to restore the heat.
ואמר רבא
And Rava said:
מפני מה אמרו אין טומנין בדבר המוסיף הבל ואפילו מבעוד יום גזירה שמא יטמין ברמץ שיש בה גחלת אמר ליה אביי ויטמין גזירה שמא יחתה בגחלים:
Why did the Sages say that one may not insulate hot water for Shabbat in something that adds heat, even while it is still day? It is a decree lest one come to cover it in hot ashes that contain a glowing ember. People may not differentiate between addition of heat by means of hot ashes and other additions of heat. Abaye said to him: Let him insulate it with hot ashes, what is the problem? Rava answered him: It is a decree lest one come to stoke the coals in order to make them burn on Shabbat and thereby violate a Torah prohibition.
תנו רבנן בין השמשות ספק מן היום ומן הלילה ספק כולו מן היום ספק כולו מן הלילה מטילין אותו לחומר שני ימים
The Sages taught a baraita which discusses the range of problems that arise with regard to the twilight period. Twilight is a period of uncertainty. It is uncertain whether it consists of both day and night, it is uncertain whether it is completely day, and it is uncertain whether it is completely night. Therefore, the Sages impose the stringencies of both days upon it. If there is a stringency that applies on either of the days, one is obligated to adhere to it during the twilight period.
ואיזהו בין השמשות משתשקע החמה כל זמן שפני מזרח מאדימין הכסיף התחתון ולא הכסיף העליון בין השמשות הכסיף העליון והשוה לתחתון זהו לילה דברי רבי יהודה רבי נחמיה אומר כדי שיהלך אדם משתשקע החמה חצי מיל רבי יוסי אומר בין השמשות כהרף עין זה נכנס וזה יוצא ואי אפשר לעמוד עליו
Nevertheless, the definition of twilight is uncertain. And what is twilight? From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun. If the lower segment of the sky has lost its color, and the upper segment has not yet lost its color, that is the twilight period. If the upper segment has lost its color, and its color equals that of the lower one, it is night; this is the statement of Rabbi Yehuda. Rabbi Neḥemya says: The duration of the twilight period is the time it takes for a person to walk half a mil after the sun sets. Rabbi Yosei says: Twilight does not last for a quantifiable period of time; rather, it is like the blink of an eye: This, night, enters and that, day, leaves, and it is impossible to calculate it due to its brevity.
אמר מר מטילין אותו לחומר שני ימים למאי הלכתא אמר רב הונא בריה דרב יהושע לענין טומאה כדתנן ראה שני ימים בין השמשות ספק לטומאה ולקרבן ראה יום אחד בין השמשות ספק לטומאה
It was taught in the baraita that the Master said: The Sages impose the stringencies of both days upon twilight. The Gemara asks: With regard to what halakha was this stated? Rav Huna, son of Rav Yehoshua, said: With regard to the matter of ritual impurity, as we learned in a mishna: With regard to a zav who saw an emission for two consecutive days during twilight, it is unclear whether it should be considered as if he only saw the emission for a single day, as perhaps twilight of the first day was part of the following day, and twilight of the second day was part of the previous day; or, whether it should be considered as two days, attributing each twilight to either the previous or the following day; or, whether it should be considered three days, as it is possible to view the twilight period as two days. By Torah law, a zav who saw two emissions is ritually impure, and all of the stringencies of a zav apply to him. If he sees a third emission, he is liable to bring an offering as part of his purification ritual. Therefore, this zav, with regard to whom there is uncertainty whether he saw emissions for one day, two days, or three days, has uncertain status with regard to both ritual impurity and to sacrifice. If he saw an emission one day during twilight, he has uncertain status with regard to ritual impurity because it may be considered two days.
הא גופה קשיא אמרת איזהו בין השמשות משתשקע החמה כל זמן שפני מזרח מאדימין הא הכסיף התחתון ולא הכסיף העליון לילה הוא והדר תנא הכסיף התחתון ולא הכסיף העליון בין השמשות אמר רבה אמר רב יהודה אמר שמואל כרוך ותני איזהו בין השמשות משתשקע החמה כל זמן שפני מזרח מאדימין והכסיף התחתון ולא הכסיף העליון נמי בין השמשות הכסיף העליון והשוה לתחתון לילה ורב יוסף אמר רב יהודה אמר שמואל הכי קתני משתשקע החמה כל זמן שפני מזרח מאדימין יום הכסיף התחתון ולא הכסיף העליון בין השמשות הכסיף העליון והשוה לתחתון לילה
The Gemara comments on the baraita cited by the Gemara. This baraita is itself difficult, self-contradictory. Initially you said, what is twilight? From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun. By inference, if the bottom segment lost its color, and the upper one has not lost its color, it is night. And then the baraita taught: If the lower segment of the sky has lost its color, and the upper segment has not yet lost its color, that is the twilight period. There is an apparent internal contradiction in the baraita. Rabba said that Rav Yehuda said that Shmuel said: In order to resolve the contradiction, unify the two statements and teach it as follows: What is twilight? From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun. If the lower segment of the sky has lost its color and the upper segment has not yet lost its color, that is also the twilight period. Only if the upper segment lost its color, and it equals that of the lower one, is it night. And Rav Yosef said that Rav Yehuda said that Shmuel said otherwise: From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun, it is day. If the lower segment of the sky has lost its color, and the upper segment has not yet lost its color, that is the twilight period. If the upper segment lost its color and it equals that of the lower one, it is night.
ואזדו לטעמייהו דאיתמר שיעור בין השמשות בכמה אמר רבה אמר רב יהודה אמר שמואל שלשה חלקי מיל מאי שלשה חלקי מיל אילימא תלתא פלגי מילא נימא מיל ומחצה אלא תלתא תילתי מילא נימא מיל אלא תלתא ריבעי מילא ורב יוסף אמר רב יהודה אמר שמואל שני חלקי מיל מאי שני חלקי מיל אילימא תרי פלגי מילא לימא מיל ואלא תרי רבעי מילא לימא חצי מיל אלא
And the Gemara remarks: In this dispute over the precise definition of twilight both Rabba and Rav Yosef follow their line of reasoning stated elsewhere. As it was stated: What is the measure of the duration of twilight? Rabba said that Rav Yehuda said that Shmuel said: The time it takes to walk three parts of a mil. The Gemara asks: What is the meaning of three parts of a mil? If you say that it refers to three halves of a mil, let him say a mil and a half. Rather, if you say that it means three-thirds of a mil, let him simply say one mil. Rather, it means three-quarters of a mil. And Rav Yosef said that Rav Yehuda said that Shmuel said: The duration of twilight is two parts of a mil. Again the Gemara asks: What is the meaning of two parts of a mil? If you say that it means two halves of a mil, let him simply say one mil. Rather, if you say that it means two-quarters of a mil, let him say instead: Half of a mil. Rather,
Masechet Shabbat is sponsored in memory of Elliot Freilich, Eliyahu Daniel ben Bar Tzion David Halevi z"l by a group of women from Kehilath Jeshurun, Manhattan.
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This month's learning is sponsored by Leah Goldford in loving memory of her grandmothers, Tzipporah bat Yechezkiel, Rivka Yoda Bat Dovide Tzvi, Bracha Bayla bat Beryl, her father-in-law, Chaim Gershon ben Tzvi Aryeh, her mother, Devorah Rivkah bat Tuvia Hacohen, her cousins, Avrum Baer ben Mordechai, and Sharon bat Yaakov.
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Shabbat 34
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ואית להו צערא לכהנים לאקופי אמר איכא איניש דידע דאיתחזק הכא טהרה אמר ליה ההוא סבא כאן קיצץ בן זכאי תורמסי תרומה עבד איהו נמי הכי כל היכא דהוה קשי טהריה וכל היכא דהוה רפי צייניה
and the priests are troubled by being forced to circumvent it, as it is prohibited for them to become ritually impure from contact with a corpse. There was suspicion, but no certainty, that a corpse was buried there. Therefore, they were unable to definitively determine its status. Rabbi Shimon said: Is there a person who knows that there was a presumption of ritual purity here? Is there anyone who remembers a time when this place was not considered ritually impure, or that at least part of it was considered to be ritually pure? An Elder said to him: Here ben Zakkai planted and cut the teruma of lupines. In this marketplace Rabbi Yoḥanan ben Zakkai, who himself was a priest, once planted lupines that were given to him as teruma. On that basis, the conclusion can be drawn that it was definitely ritually pure. Rabbi Shimon, like Jacob, also did so and took steps to improve the city and examined the ground (Tosafot). Everywhere that the ground was hard, he pronounced it ritually pure as there was certainly no corpse there, and every place that the ground was soft, he marked it indicating that perhaps a corpse was buried there. In that way, he purified the marketplace so that even priests could walk through it.
אמר ההוא סבא טיהר בן יוחי בית הקברות אמר ליה אילמלי (לא) היית עמנו ואפילו היית עמנו ולא נמנית עמנו יפה אתה אומר עכשיו שהיית עמנו ונמנית עמנו יאמרו זונות מפרכסות זו את זו תלמידי חכמים לא כל שכן יהב ביה עיניה ונח נפשיה נפק לשוקא חזייה ליהודה בן גרים אמר עדיין יש לזה בעולם נתן בו עיניו ועשהו גל של עצמות:
A certain Elder said in ridicule and surprise: Ben Yoḥai purified the cemetery. Rabbi Shimon got angry and said to him: Had you not been with us, and even had you been with us and were not counted with us in rendering this ruling, what you say is fine. You could have said that you were unaware of my intention or that you did not agree or participate in this decision. Now that you were with us and were counted with us in rendering this ruling, you will cause people to say that Sages are unwilling to cooperate with one another. They will say: If competing prostitutes still apply makeup to each other to help one another look beautiful, all the more so that Torah scholars should cooperate with each other. He directed his eyes toward him and the Elder died. Rabbi Shimon went out to the marketplace and he saw Yehuda, son of converts, who was the cause of this entire incident. Rabbi Shimon, said: This one still has a place in the world? He directed his eyes toward him and turned him into a pile of bones.
מתני׳ שלשה דברים צריך אדם לומר בתוך ביתו ערב שבת עם חשכה עשרתם ערבתם הדליקו את הנר ספק חשכה ספק אינו חשכה אין מעשרין את הודאי ואין מטבילין את הכלים ואין מדליקין את הנרות אבל מעשרין את הדמאי ומערבין וטומנין את החמין:
MISHNA: There are three things a person must say in his home on Shabbat eve at nightfall and not before. The mishna elaborates: He should ask the members of his household, have you tithed the crop that required tithing? Have you placed the eiruv for joining the courtyards and joining the Shabbat borders? If you have done so, light the lamp in honor of Shabbat. The Sages stated a principle: If the time arrives on Friday when there is uncertainty whether it is nightfall and uncertainty whether it is not yet nightfall, one may not tithe the crop that has definitely not been tithed, and one may not immerse ritually impure vessels in a ritual bath to render them ritually pure, and one may not light the Shabbat lights. However, one may tithe demai, doubtfully tithed produce, which must be tithed due to mere suspicion. And one may place an eiruv and insulate the hot water to be used on Shabbat.
גמ׳ מנא הני מילי אמר רבי יהושע בן לוי אמר קרא וידעת כי שלום אהלך ופקדת נוך ולא תחטא אמר רבה בר רב הונא אף על גב דאמור רבנן שלשה דברים צריך אדם לומר וכו׳ צריך למימרינהו בניחותא כי היכי דליקבלינהו מיניה אמר רב אשי אנא לא שמיע לי הא דרבה בר רב הונא וקיימתי מסברא
GEMARA: The Gemara attempts to clarify: From where are these matters, that one must ask these questions in his home at nightfall of Shabbat, derived? Rabbi Yehoshua ben Levi said: As the verse said: “And you shall know that your tent is in peace; and you shall visit your habitation, and shall not sin” (Job 5:24). From here it is derived that one should visit his habitation, i.e., ask in his home, so that he will not come to sin. Rabba bar Rav Huna said: Although the Sages said that there are three things a person should, indeed he is required to, say in his home on Shabbat eve at nightfall, one must say them calmly so that the members of his household will accept them from him. If he says them harshly, his family members may mislead him and cause him to sin. Rav Ashi said: I did not hear this halakha of Rabba bar Rav Huna, but I fulfilled it based on my own reasoning.
הא גופא קשיא אמרת שלשה דברים צריך אדם לומר בתוך ביתו ערב שבת עם חשכה עם חשכה אין ספק חשכה ספק אינו חשכה לא והדר תני ספק חשכה ספק אינו חשכה מערב:
The Gemara asks: This mishna itself is difficult, as it contains an internal contradiction. On the one hand, you stated initially that there are three things a person must say in his home before Shabbat at nightfall, and this means: At nightfall, i.e., before nightfall, yes, he should say those things; when there is uncertainty whether it is nightfall and uncertainty whether it is not yet nightfall, no, he should not say them. Even if one were to ask then, it is no longer permitted to correct these matters. And then it taught: When there is uncertainty whether it is nightfall and uncertainty whether it is not yet nightfall, one may place an eiruv. One may correct the situation even then. Why did the mishna restrict asking these questions to an earlier time?
סימן בגופיא זימרא ציפרא בחבלא דמילתא:
Incidentally, prior to answering this question, the Gemara lists all of the other halakhot in tractate Shabbat stated by the Sage who answers the question, with the mnemonic: Self, pruning, bird, cord, silk.
אמר רבי אבא אמר רב חייא בר אשי אמר רב לא קשיא כאן בעירובי תחומין כאן בעירובי חצרות
Rabbi Abba said that Rabbi Ḥiyya bar Ashi said that Rav said: This is not difficult and there is no contradiction here. Here, at the beginning of the mishna, where it indicates that the eiruv can only be placed while it is still day, it is referring to the joining of Shabbat boundaries, which is based on a Torah law. Therefore, one must place this eiruv while it is definitely day. And here, where the mishna said that it is permitted even when it is uncertain whether or not it is already nighttime, it is referring to the joining of courtyards, which is more lenient and based merely on a stringency.
ואמר רבא אמרו לו שנים צא וערב עלינו לאחד עירב עליו מבעוד יום ולאחד עירב עליו בין השמשות זה שעירב עליו מבעוד יום נאכל עירובו בין השמשות וזה שעירב עליו בין השמשות נאכל עירובו משחשכה שניהם קנה עירוב
In connection to this, the Gemara cites the halakha that Rava said in order to emphasize the rabbinic aspect of the halakhot of eiruv: One to whom two people said: Go and place an eiruv, a joining of courtyards (Rabbeinu Ḥananel), for us. For one of them he placed an eiruv while it was still day, and for one he placed an eiruv at twilight, when it is uncertain whether it is day or night. The one for whom he placed an eiruv while it was still day had his eiruv eaten during twilight, and the one for whom he placed an eiruv during twilight had his eiruv eaten after nightfall. The principle is as follows: Whether or not an eiruv takes effect is determined at the moment that Shabbat begins. If one placed the eiruv beforehand, and it remains intact at the moment Shabbat begins, the eiruv is in effect. However, if the eiruv that was placed at the appropriate time was eaten during twilight, it is problematic. Twilight is a period of uncertainty. There is uncertainty whether it is day, and consequently the eiruv was not in place at the moment that Shabbat began, or whether it is night, and it was in place. In the latter case, there is still uncertainty as to whether or not the eiruv was in place prior to Shabbat, so that it could take effect at all. In that case, Rava ruled that both of them acquired the eiruv.
מה נפשך אי בין השמשות יממא הוא בתרא ליקני קמא לא ליקני ואי בין השמשות ליליא הוא קמא ליקני בתרא לא ליקני בין השמשות ספקא הוא וספקא דרבנן לקולא:
The Gemara is surprised by this: Whichever way you look at it, this ruling is difficult. If the twilight period is considered day, let the latter one acquire his eiruv, but let the first one not acquire his because his eiruv was eaten while it was still day. And if the twilight period is night, let the first one acquire his eiruv, but let the latter one not acquire his eiruv because his was not placed before Shabbat. In any event, it is impossible for the eiruv in both of these cases to be valid. The Gemara answers this according to Rava’s position: The status of twilight is uncertain, as it is unknown whether it is day, or night, or both, and uncertainty in the case of a rabbinic ordinance is ruled leniently. Therefore, in both cases the eiruv is acquired.
(ואמר) רבא מפני מה אמרו אין טומנין בדבר שאינו מוסיף הבל משחשכה גזרה שמא ירתיח אמר ליה אביי אי הכי בין השמשות נמי ניגזר אמר ליה סתם קדירות רותחות הן
And Rava said: Why did they say that one may not insulate hot water even in something that does not add heat, but only retains the pre-existing heat, from nightfall on Friday? It is a decree lest one come to boil the pot on Shabbat. Abaye said to him: If so, if it is due to concern that one may boil it, then during twilight we should also issue a decree and prohibit insulating in something that does not add heat. Rava said to him: During twilight, there is no reason to be concerned because at that time most pots are boiling, as they have just been taken off of the fire. Later at night the pots cool down and it is conceivable that one may come to boil them in order to restore the heat.
ואמר רבא
And Rava said:
מפני מה אמרו אין טומנין בדבר המוסיף הבל ואפילו מבעוד יום גזירה שמא יטמין ברמץ שיש בה גחלת אמר ליה אביי ויטמין גזירה שמא יחתה בגחלים:
Why did the Sages say that one may not insulate hot water for Shabbat in something that adds heat, even while it is still day? It is a decree lest one come to cover it in hot ashes that contain a glowing ember. People may not differentiate between addition of heat by means of hot ashes and other additions of heat. Abaye said to him: Let him insulate it with hot ashes, what is the problem? Rava answered him: It is a decree lest one come to stoke the coals in order to make them burn on Shabbat and thereby violate a Torah prohibition.
תנו רבנן בין השמשות ספק מן היום ומן הלילה ספק כולו מן היום ספק כולו מן הלילה מטילין אותו לחומר שני ימים
The Sages taught a baraita which discusses the range of problems that arise with regard to the twilight period. Twilight is a period of uncertainty. It is uncertain whether it consists of both day and night, it is uncertain whether it is completely day, and it is uncertain whether it is completely night. Therefore, the Sages impose the stringencies of both days upon it. If there is a stringency that applies on either of the days, one is obligated to adhere to it during the twilight period.
ואיזהו בין השמשות משתשקע החמה כל זמן שפני מזרח מאדימין הכסיף התחתון ולא הכסיף העליון בין השמשות הכסיף העליון והשוה לתחתון זהו לילה דברי רבי יהודה רבי נחמיה אומר כדי שיהלך אדם משתשקע החמה חצי מיל רבי יוסי אומר בין השמשות כהרף עין זה נכנס וזה יוצא ואי אפשר לעמוד עליו
Nevertheless, the definition of twilight is uncertain. And what is twilight? From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun. If the lower segment of the sky has lost its color, and the upper segment has not yet lost its color, that is the twilight period. If the upper segment has lost its color, and its color equals that of the lower one, it is night; this is the statement of Rabbi Yehuda. Rabbi Neḥemya says: The duration of the twilight period is the time it takes for a person to walk half a mil after the sun sets. Rabbi Yosei says: Twilight does not last for a quantifiable period of time; rather, it is like the blink of an eye: This, night, enters and that, day, leaves, and it is impossible to calculate it due to its brevity.
אמר מר מטילין אותו לחומר שני ימים למאי הלכתא אמר רב הונא בריה דרב יהושע לענין טומאה כדתנן ראה שני ימים בין השמשות ספק לטומאה ולקרבן ראה יום אחד בין השמשות ספק לטומאה
It was taught in the baraita that the Master said: The Sages impose the stringencies of both days upon twilight. The Gemara asks: With regard to what halakha was this stated? Rav Huna, son of Rav Yehoshua, said: With regard to the matter of ritual impurity, as we learned in a mishna: With regard to a zav who saw an emission for two consecutive days during twilight, it is unclear whether it should be considered as if he only saw the emission for a single day, as perhaps twilight of the first day was part of the following day, and twilight of the second day was part of the previous day; or, whether it should be considered as two days, attributing each twilight to either the previous or the following day; or, whether it should be considered three days, as it is possible to view the twilight period as two days. By Torah law, a zav who saw two emissions is ritually impure, and all of the stringencies of a zav apply to him. If he sees a third emission, he is liable to bring an offering as part of his purification ritual. Therefore, this zav, with regard to whom there is uncertainty whether he saw emissions for one day, two days, or three days, has uncertain status with regard to both ritual impurity and to sacrifice. If he saw an emission one day during twilight, he has uncertain status with regard to ritual impurity because it may be considered two days.
הא גופה קשיא אמרת איזהו בין השמשות משתשקע החמה כל זמן שפני מזרח מאדימין הא הכסיף התחתון ולא הכסיף העליון לילה הוא והדר תנא הכסיף התחתון ולא הכסיף העליון בין השמשות אמר רבה אמר רב יהודה אמר שמואל כרוך ותני איזהו בין השמשות משתשקע החמה כל זמן שפני מזרח מאדימין והכסיף התחתון ולא הכסיף העליון נמי בין השמשות הכסיף העליון והשוה לתחתון לילה ורב יוסף אמר רב יהודה אמר שמואל הכי קתני משתשקע החמה כל זמן שפני מזרח מאדימין יום הכסיף התחתון ולא הכסיף העליון בין השמשות הכסיף העליון והשוה לתחתון לילה
The Gemara comments on the baraita cited by the Gemara. This baraita is itself difficult, self-contradictory. Initially you said, what is twilight? From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun. By inference, if the bottom segment lost its color, and the upper one has not lost its color, it is night. And then the baraita taught: If the lower segment of the sky has lost its color, and the upper segment has not yet lost its color, that is the twilight period. There is an apparent internal contradiction in the baraita. Rabba said that Rav Yehuda said that Shmuel said: In order to resolve the contradiction, unify the two statements and teach it as follows: What is twilight? From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun. If the lower segment of the sky has lost its color and the upper segment has not yet lost its color, that is also the twilight period. Only if the upper segment lost its color, and it equals that of the lower one, is it night. And Rav Yosef said that Rav Yehuda said that Shmuel said otherwise: From when the sun sets, as long as the eastern face of the sky is reddened by the light of the sun, it is day. If the lower segment of the sky has lost its color, and the upper segment has not yet lost its color, that is the twilight period. If the upper segment lost its color and it equals that of the lower one, it is night.
ואזדו לטעמייהו דאיתמר שיעור בין השמשות בכמה אמר רבה אמר רב יהודה אמר שמואל שלשה חלקי מיל מאי שלשה חלקי מיל אילימא תלתא פלגי מילא נימא מיל ומחצה אלא תלתא תילתי מילא נימא מיל אלא תלתא ריבעי מילא ורב יוסף אמר רב יהודה אמר שמואל שני חלקי מיל מאי שני חלקי מיל אילימא תרי פלגי מילא לימא מיל ואלא תרי רבעי מילא לימא חצי מיל אלא
And the Gemara remarks: In this dispute over the precise definition of twilight both Rabba and Rav Yosef follow their line of reasoning stated elsewhere. As it was stated: What is the measure of the duration of twilight? Rabba said that Rav Yehuda said that Shmuel said: The time it takes to walk three parts of a mil. The Gemara asks: What is the meaning of three parts of a mil? If you say that it refers to three halves of a mil, let him say a mil and a half. Rather, if you say that it means three-thirds of a mil, let him simply say one mil. Rather, it means three-quarters of a mil. And Rav Yosef said that Rav Yehuda said that Shmuel said: The duration of twilight is two parts of a mil. Again the Gemara asks: What is the meaning of two parts of a mil? If you say that it means two halves of a mil, let him simply say one mil. Rather, if you say that it means two-quarters of a mil, let him say instead: Half of a mil. Rather,