INTERRUPTING BETWEEN THE TWO TEFILIN
Version #1 - Rashi - (Rav Chisda): If one talked in between the two Tefilin (i.e. after putting on the Shel Yad before putting on the Shel Rosh), he must make another blessing ('Al Mitzvas Tefilin' on the Shel Rosh).
Question: R. Chiya brei d'Rav Huna taught that (normally) 'Lehani'ach Tefilin' is made on the Shel Yad, and 'Al Mitzvas Tefilin' on the Shel Rosh!
Answer (Abaye and Rava): No, that is when he talked in between. If he did not talk, he blesses only on the Shel Yad.
Version #2 - R. Tam - (Rav Chisda): If one talked in between the two Tefilin, he must repeat the blessing ('Lehani'ach Tefilin'; he also blesses 'Al Mitzvas Tefilin', which we always make on the Shel Rosh).
Question: R. Chiya brei d'Rav Huna taught that 'Lehani'ach Tefilin' is made on the Shel Yad, and (only) 'Al Mitzvas Tefilin' on the Shel Rosh!
Answer (Abaye and Rava): That is when he did not talk in between. If he talked, he makes two blessings on the Shel Rosh. (end of Version #2)
(Beraisa): If one talked in between the two Tefilin, this is an Aveirah that disqualifies him from fighting in war. (Tosfos - because he caused an unnecessary blessing; Rashi explains, he is disqualified if he did not repeat the blessing, for then he fulfilled the Mitzvah of head Tefilin without a blessing).
(Beraisa): One puts on the Shel Yad before the Shel Rosh. When removing them, he removes the Shel Rosh before the Shel Yad.
Question: We understand the first law - "u'Kshartam l'Os Al Yadecha (and then) v'Hayu l'Totafos Bein Einecha";
However, why must one remove the Shel Rosh first?
Answer (Rabah): "V'Hayu (plural) l'Totafos Bein Einecha" - whenever Tefilin are on your head, you are wearing both.
WHEN DOES THE MITZVAH APPLY?
(Beraisa): One blesses on Tefilin from the (earliest normal) time to wear them (when it is light enough to recognize an acquaintance four Amos away):
If someone had to start traveling early (before the proper time to wear them), and for the safety of the Tefilin he must wear them, he wears them. When the proper time comes, he touches them and blesses.
Question: Until when may one wear Tefilin?
Answer #1: It is permitted until sundown.
Answer #2 (R. Yakov): It is permitted until people cease to walk outside.
Answer #3 (Chachamim): It is permitted until the time that people normally go to sleep.
Chachamim and R. Yakov agree (with the first Tana) that if one removed his Tefilin, he may not put them on again after sundown. (Rashi - the Mitzvah of Tefilin does not apply at night; Tosfos - it applies at night, but Chachamim decreed against putting on Tefilin at night.)
Version #1 (Rav Nachman): The Halachah follows R. Yakov.
Rav Chisda and Rabah bar Rav Huna wore Tefilin during prayer at night.
Version #2 (Rav Nachman): The Halachah does not follow R. Yakov.
Question: Rav Chisda and Rabah (bar Rav Huna) wore Tefilin during prayer at night!
Answer: They argue with Rav Nachman.
Question: Rabah does not permit wearing Tefilin at night!
(Rabah bar Rav Huna): When it is doubtfully night, one need not remove Tefilin, and one may not put them on.
Inference: When it is definitely night, one must remove Tefilin!
Answer: Rabah teaches about Erev Shabbos.
Question: When does he hold that the Mitzvah applies?
If he holds that it applies at night, he should hold that it applies also on Shabbos;
If he holds that the Mitzvah does not apply on Shabbos, he should hold that it does not apply at night, either!
This is because the same source (that a Tana uses) to exclude Shabbos excludes night.
(Beraisa - R. Yosi ha'Galili): (After the Mitzvah of Tefilin it says) "v'Shamarta Es ha'Chukah ha'Zos l'Mo'adah mi'Yamim Yamimah." 'Yamim' excludes nights. "Mi'Yamim" excludes some days, i.e. Shabbos and Yom Tov.
R. Akiva says, this refers to the 'Chok' (statute) of Pesach (which was discussed before Tefilin).
Answer: Rabah holds like R. Akiva, who learns from another source that the Mitzvah does not apply on Shabbos.
(Beraisa - R. Akiva) Suggestion: Perhaps one should wear Tefilin on Shabbos and Yom Tov!
Rejection: "V'Hayah l'Os Al Yadcha..." - the Mitzvah applies only on days when Yisrael need an Os (sign of their closeness to Hash-m), but not Shabbos or Yom Tov, which are themselves signs.
(R. Elazar): One who wears Tefilin at night transgresses an Aseh;
(R. Yochanan): He transgresses a Lav.
Suggestion: They argue about R. Avin's law.
(R. Avin): Wherever it says "Hishamer", "Pen" or "Al", this is a Lav.
R. Yochanan holds like R. Avin, and R. Elazar does not.
Rejection: No, both hold like R. Avin;
R. Elazar holds that when it says "Hishamer" regarding a Lav, this is a Lav. "Hishamer" regarding an Aseh is an Aseh;
R. Yochanan holds that in both cases it is a Lav.
(R. Elazar): One may wear Tefilin at night in order to guard them.
Ravina: I saw Rav Ashi put on (Shitah Mekubetzes - wearing) Tefilin at night. I asked if this was in order to guard them, and he said 'yes';
I could tell that really, it wasn't in order to guard them. He holds that the Halachah permits this, but we do not say this to one who asks.
(Rabah bar Rav Huna): One must constantly touch Tefilin (when he wears them). We learn from a Kal va'Chomer from the Tzitz;
The Tzitz has Hash-m's name on it only once, yet the Torah says "v'Hayah Al Mitzcho Tamid." The Kohen Gadol may not cease to think about it;
Hash-m's name is written 21 times in each Tefilin (of the hand and head). All the more so one must constantly be aware of them!
ON WHICH HAND DO WE WEAR TEFILIN?
(Beraisa): (Tefilin are tied on) "Yadcha" - the left arm.
Suggestion: Perhaps it refers to the right arm!
Rejection: It says "Af Yadi Yasdah Eretz vi'Ymini Tipchah Shamayim", and "Yadah la'Yased Tishlachnah vi'Yminah Lehalmus Amelim", and "Lamah Sashiv Yadcha vi'Yminecha mi'Kerev Chekcha Chale" - Yemin refers to the right, and Yad (unspecified) refers to the left.