Shabbat Parashat Tazria Metzora| 5763
Ask the Rabbi
Question: My son will soon be bar-mitzvah. He writes and does most things with his left hand but does many things with his right. On which arm does he lay tefillin?
Answer: Mazal tov. Your case appears straight-forward, although we request a list of things he does with each hand and those he does equally with both. Then we can give a final ruling. First, allow us to present a little background.
All agree that a “righty” lays tefillin on his left hand, but three sources are brought for this halacha (Menachot 36b-37a). Tanna Kamma says the word “yadchah” (where we are to fasten the tefillin)means the left arm. R. Natan learns from the “attachment of p'sukim” (hekeish), which compares the hand one uses to fasten the tefillin onto the opposite arm to the hand one uses to write a mezuzah. Most people write with their right hand and, thus, fasten the tefillin onto their left arm. R. Ashi learns from the extra letter “heh” in “yadchah” (Shemot 13:16) that tefillin go on the "yad keiha"(weaker hand), usually the left. A “lefty’s” weak hand is the right.
A major machloket exists among the Rishonim about one who writes with one hand and does most other activities with the other. The Sefer Hatrumah says to lay the tefillin on the overall weaker hand, without special emphasis on writing. R. Yechiel of Paris says that one who writes with his right hand lays on his left arm even if he does everything else with his left (see Tur, Orach Chayim 27). The Shulchan Aruch (27:6) brings both opinions, but he and the Rama favor R. Yechiel’s opinion to follow one’s writing. Thus, your case should be simple– your son puts the tefillin on his right arm.
However, despite the stature of the Shulchan Aruch and Rama, some major poskim question their p'sak. It appears that the two opinions in Rishonim are based on two of the sources in the aforementioned gemara, one stressing writing and the other stressing general strength/skill. The Gra (OC 27) demonstrates that the majority of opinions follows Rav Ashi, that we place the tefillin on the overall weaker hand. Furthermore, the Bach (on the Tur, ibid.) argues on the Shulchan Aruch’s understanding of R. Yechiel. The Bach says that R. Yechiel accepted both the source of “writing-fastening” and that of “the weak hand” and, only when one is a “lefty” in both regards, does he lay on the right. With a “twist” on this approach, R. Moshe Feinstein (Igrot Moshe YD IV, 11) understands that one who writes with one hand but does most work with the other is deemed ambidextrous (sholet b'shtei yadav) and lays on the left arm (Menachot 37a). The exact parameters of sholet b'shtei yadav are not fully clear and, according to certain opinions and in certain cases, may cause one who considers himself a “lefty” to be treated like a “righty.” For example, there are different opinions about one who writes with both hands but prefers his left or one who writes script with one hand and prints with the other. So we ask for more detailed information and hope that the situation will turn out clear cut as, according to most poskim, there's no easy way to cover all bases.
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