Q&A from the Bais HaVaad Halacha Hotline

Arm Wrestling

February 19, 2026

Q I developed a condition that affected my handwriting ability, so instead of writing, I type on my phone, which I tend to do with my left hand. But I perform all other tasks with my right. Where should I put my tfillin?

A Several sources are given in the Gemara (Menachos 37a) for the requirement that tfillin be worn on the left arm; two are cited by the poskim:

• The word “yadcha” can be read yad keihah (the weak arm)
• “Ukshartam…uchsavtam” indicates that the hand used for writing also ties the tfillin, which would mean they are worn on the opposite arm

Based on these sources, the Gemara says a left‑handed person wears tfillin on his right arm, because a) that is his weaker one, and b) he writes with his left. The Rishonim debate the case of one who writes with one hand but does everything else with the other. The Shulchan Aruch (O.C. 27:6) cites two views:

• He lays tfillin on the weaker arm
• Writing is determinative (the Rama says this is the minhag)

The Biur Halacha (ibid. s.v. Veyeish) says that writing in this context might refer to the kind of writing used for tfillin, i.e., safrus—which would mean that if someone can’t write that way, his ordinary handwriting wouldn’t matter. But he rejects this notion, because the poskim don’t mention it.

He then wonders whether someone who is unable to write and can only scribble is considered to be writing and so wears tfillin on the opposite side. Interestingly, he draws a comparison to the melacha of koseiv on Shabbos, where making any meaningful symbol is included in the prohibition (Rambam Hil. Shabbos 11:10). Yet he remains uncertain, and he concludes that such a person should don tfillin on his left like most people, because we can also adduce the view of those poskim that say writing is not determinative.

According to some, typing on a phone on Shabbos constitutes the melacha of koseiv, but that is only because the tapping produces fully-formed letters. The act of tapping is not, however, a ma’asei ksivah, so it does not determine your handedness for tfillin. If you had always written right-handed, put tfillin on your left. If you wrote with your left, the halacha depends on multiple factors, so ask your rav.