THE TIME FOR SAYING KERI'AS SHEMA
(Mishnah) Question: When do we say Keri'as Shema at night?
Answer #1 (R. Eliezer): The Mitzvah is from the time at which Kohanim may eat Terumah until the end of the first Mishmar (these will be explained).
Answer #2 (Chachamim): The time extends until midnight.
Answer #3 (R. Gamliel): The time extends until dawn.
A case occurred: R. Gamliel's sons came home from a wedding after midnight (they had not said Shema).
R. Gamliel: You are obligated to say it now;
In fact, wherever Chachamim said "until midnight," the Mitzvah (mid'Oraisa) is until dawn:
Chelev (of Korbanos) and limbs (of an Olah) may be burned on the Mizbe'ach until dawn;
Any Korban that may be eaten for one day and a night is permitted until dawn.
Question: If so, why did Chachamim say, "until midnight"?
Answer: This is to distance people from transgression (lest dawn arrive before one performs the Mitzvah).
(Gemara) Question #1: It is unreasonable to ask about the time of Keri'as Shema before teaching that it is a Mitzvah! What is the Tana's source for the obligation to recite Shema?
Question #2: Why does the Tana first ask about the time for the nighttime Shema? He should first ask about the time for the morning Shema! (We find that the Torah teaches about the morning Tamid before the afternoon Tamid.)
Answer #1 (to both questions): The Tana expounds the verse, "uv''Shochbecha uv''Kumecha." Therefore, he first asks about the time of Shechivah (going to sleep).
Answer #2 (to Question #2): He learns from creation of the world that night comes first, as it says, "va'Yehi Erev va'Yehi Voker Yom Echad."
Question (Mishnah): In the morning, there are two Berachos before Shema and one after; at night, there are two Berachos before and two after.
According to both answers, the Tana should teach about the Berachos of the nighttime Shema first!
Answer: The Tana begins our Mishnah with the nighttime Shema and concludes with the morning Shema; once he discusses the morning Shema, he teaches all its laws, then returns to discuss the nighttime Shema.
WHEN KOHANIM MAY EAT TERUMAH
(Mishnah - R. Eliezer): The Mitzvah is from when Kohanim may eat Terumah...
(The time Kohanim may eat Terumah always refers to a Kohen who was Tamei and immersed; he is a Tevul Yom and may not even touch Terumah until night.)
Question: Kohanim may eat at Tzeis ha'Kochavim (when stars become visible at night) -- the Mishnah should say this explicitly!
Answer: The Tana taught the time of Shema indirectly, in order to teach as well that Kohanim may eat Terumah at Tzeis ha'Kochavim;
One might have thought that the Heter for a Mechusar Kipurim (one who must bring Korbanos to finish his Taharah, e.g. a Zav) to eat Terumah comes [during the day], when he brings the Korbanos. The Mishnah teaches that this is not so; the Heter is the night after he immerses, before bringing the Korbanos.
(Beraisa): "u'Va ha'Shemesh v'Taher" -- the setting of the sun is required before he can eat Terumah; the Korban is not required.
Version #1 (Rashi) Question: How does the Tana know that "u'Va ha'Shemesh" refers to the setting of the sun, and "v'Taher" refers to completion of the day?
Perhaps "u'Va ha'Shemesh" refers to the rising of the sun (the day after immersion), and "v'Taher" refers to the person (who completes his Taharah by bringing Korbanos)!
Version #2 (Tosfos) Question: How do we know that "u'Va ha'Shemesh" refers to Tzeis ha'Kochavim, and "v'Taher" refers to completion of the day?
Perhaps "u'Va ha'Shemesh" refers to sundown, and "v'Taher" refers to the person (whose Taharah is complete, even though it is still day)! (End of Version #2)
Answer (Rabah bar Rav Shila): If so, the Torah would have said "va'Yetaher" (to show clearly that it refers to the person);
Rather, it says "v'Taher" to refer to the day; this is like people say, "The sun went down and the day is finished."
In Eretz Yisrael, they did not hear Rabah's teaching, and thus they had a question.
Question: Does "u'Va ha'Shemesh" refer to Tzeis ha'Kochavim, and "v'Taher" to the completion of the day, or does "u'Va ha'Shemesh" refer to sunset (Tosfos; Rashi - sunrise), and "v'Taher" to the person?
Answer (Beraisa): A sign [of when Kohanim may eat] is Tzeis ha'Kochavim.
This shows that the verse refers to Tzeis ha'Kochavim and the completion of the day.
THE EARLIEST TIME FOR THE NIGHTTIME SHEMA
(Mishnah - R. Eliezer): The Mitzvah [of Shema] is from the time at which Kohanim may eat Terumah.
Contradiction (Beraisa #1): Question: When do we say Keri'as Shema at night?
Answer: The Mitzvah is from when an Ani (a poor person, who eats without the light of a lamp) begins to eat bread with salt, until he finishes his meal.
Surely, the Beraisa argues [with all opinions in our Mishnah] about the latest time for Shema (an Ani's meal does not last four hours);
Must we say that it also argues about the earliest time for Shema?
Answer: No, the times of an Ani (when he eats) and Kohen (when he may eat Terumah) are the same.
Contradiction (Beraisa #2): Question: From when may we say Shema at night?
Answer #1 (R. Meir): The Mitzvah begins when people begin to eat bread on Shabbos night (which is early, since everything is already prepared);
Answer #2 (Chachamim): It is from when Kohanim may eat Terumah; a sign for this time is Tzeis ha'Kochavim;
A support for this, but not a proof, is the verse, "va'Anachnu Osim ba'Melachah... me'Alos ha'Shachar Ad Tzeis ha'Kochavim" (people work from dawn until nightfall);
It also says, "v'Hayu Lanu ha'Lailah Mishmar veha'Yom Melachah."
Question: Why do we need the second verse?
Answer: One might have thought that night begins before Tzeis ha'Kochavim (and day begins after dawn), and they were working more than usual (to build the Beis ha'Mikdash). The second verse shows that this is not so.
We are thinking that an Ani eats at the same time as regular people [eat on Shabbos].
Summation of question: If the times of Ani and Kohen are the same, then Chachamim agree with R. Meir!
Rather, we must say that they are different.
Answer: Really, they are the same. The times of Ani and regular people are different.
Question: The times of Ani and Kohen are not the same!
(Beraisa #3) Question: From when may we say Shema at night?
Answer #1 (R. Eliezer): The Mitzvah begins at Kidush ha'Yom (when the prohibitions of Shabbos take effect on Shabbos night, i.e. at Bein ha'Shemashos, which is Safek day, Safek night).
Answer #2 (R. Yehoshua): It begins when Kohanim may eat Terumah;
Answer #3 (R. Meir): It begins at the [latest] time [during the day] that Kohanim may immerse to eat Terumah [that night];
Objection (R. Yehudah): They must immerse during the day [whereas Shema must be said at night]!
Answer #4 (R. Chanina): It begins when an Ani comes in to eat bread with salt.
Answer #5 (Rav Achai): It begins when most people come in to eat.
Summation of question: If the times of Ani and Kohen are the same, then R. Yehoshua and R. Chanina say the same thing!
Conclusion: The times are different.
Question: Which of them is the latest time?
Answer: Presumably, Ani is latest, for if not, then R. Eliezer and R. Chanina say the same thing! (Surely an Ani does not stop working before Bein ha'Shemashos. Bein ha'Shemashos is shortly before Tzeis ha'Kochavim, so it is unreasonable that three Tana'im argue about times that are so close together!)
(Beraisa - R. Yehudah) Objection: They must immerse during the day! (Bein ha'Shemashos extends for nine minutes; Kohanim must immerse before it starts, Shema is said when people go to sleep when it is definitely night, at least nine minutes later!)
Question: This is a valid objection! (How can R. Meir answer it?)
Answer: R. Meir disagrees with R. Yehudah's opinion of Bein ha'Shemashos, he holds like R. Yosi:
(R. Yosi): Bein ha'Shemashos is like an eye's wink -- the new day enters immediately after the previous day ends. (Therefore, Kohanim can immerse until nightfall, when people go to sleep.)
Question: R. Meir (in Beraisos #2 and #3) contradicts himself!
Answer: Tana'im argue about R. Meir's opinion.
Question: R. Eliezer (in our Mishnah and Beraisa #3) contradicts himself!
Answer #1: Tana'im argue about R. Eliezer's opinion.
Answer #2: In our Mishnah, R. Eliezer teaches only about the latest time for Shema; the earliest time is according to the [anonymous] first Tana.