Menachos Daf 37 מנחוס דַף 37

A Baraisa teaches that when the Torah says to place תפלין של יד on "ידך" – your hand, it means the left, because several pesukim contrast "יד" with "ימין" – right hand, implying that "יד" indicates the left hand. Rebbe Nosson says that the words וקשרתם...וכתבתם – and you shall bind them…and you shall write them (מזוזות) compare the two terms: מה כתיבה בימין אף קשירה בימין – just as writing [a mezuzah] is usually done with the right hand, so too binding [tefillin] is done with the right hand. Since he binds with his right hand, the placing must be onto the left arm. Rav Ashi says the spelling of "ידכה" with a hei alludes to כהה – the weak left arm. A Baraisa teaches that אטר – a left-handed person places tefillin onto his right arm, שהוא שמאלו – because it is considered his “left” hand, since it is the weaker of the two. Another Baraisa which states that an אטר should place tefillin on his left arm is referring to שולט בשתי ידיו – one who controls both his hands, i.e., an ambidextrous person.

A Baraisa defines "על ידך" as referring specifically to the קיבורת – the biceps muscle. The place for theשל ראש , expressed as "בין עיניך" – between your eyes, means the "קדקד", which is further explained as מקום שמוחו של תינוק רופס – the place where an infant’s skull is soft. A Baraisa gives several sources that "ידך" refers to the biceps muscle: (1) We compare תפלין של יד with תפלין של ראש. Just as the של ראש is placed בגובה שבראש – on the high part of the head, the של יד is also placed בגובה שביד – on the high part of the arm. (2) The passuk says: והיה לך לאות – and it shall be a sign for you, which implies לך לאות ולא לאחרים לאות – for you the wearer, it shall be a sign, but it shall not be a sign for others. Thus, it is placed on the biceps muscle, a location which is ordinarily not visible to others, and not on the hand (however, the תפלין may be visible). (3) The passuk says to place Hashem’s words "על לבבכם" – on your hearts, then it says "וקשרתם" – and you shall bind (תפלין), teaching שתהא שימה כנגד הלב – that the placing shall be opposite the heart. Two sources are given for the correct place for the של ראש.

The Mishnah on Daf 28a stated that all four ציציות are מעכב each other, שארבעתן מצוה אחת – because the four of them are one mitzvah, while Rebbe Yishmael said they are four mitzvos. Amoraim offer three practical differences between these opinions: (1) Using סדין בציצית – a linen sheet with wool tzitzis. If the garment is missing one ציצית, and the other three contain שעטנז, the Tanna Kamma holds he transgresses the prohibition to wear שעטנז, since he is not fulfilling the mitzvah of ציצית, whereas Rebbe Yishmael says he fulfills three mitzvos with the ציצית on the garment, and does not transgress שעטנז. (2) טלית בעלת חמש – a five cornered-cloak. According to the Tanna Kamma, only four of the corners require ציצית, while Rebbe Yishmael would require ציצית at all five corners, since each corner is an independent mitzvah. (3) Rav Huna ruled that one who goes out into רשות הרבים on Shabbos wearing טלית שאינה מצוייצת כהלכתה – a garment which is not properly fringed is liable for a חטאת (because the invalid ציצית is considered a burden). These Tannaim disagree if this would apply where ציצית are on three of the four corners.