The Halacha below was derived from multiple classes orated by Rabbi Eli Mansour in the Bekiim B'Halacha series. Click on any of the recording dates below to hear the original audio files, which are the sources for today's Halacha below. 04/02/25 ; 04/03/25 ; 04/07/25 ; 04/09/25 ; 05/04/25 Which Arm Should a Person Use for Tefillin—And What If He Is Left-Handed, Ambidextrous, or Disabled? The Torah commands us to bind Tefillin "on your arm." But which arm? That question is settled by our Sages: the arm referred to is the weaker arm. So for a right-handed person, Tefillin go on the left arm, and for a left-handed person, they go on the right. This Halacha examines how the decision is made, and how the Halacha applies to left-handed people, those who are ambidextrous, and individuals with limited use of one arm due to injury, paralysis, or amputation. What Is the Halachic Rule for Determining Which Arm to Use? The verse says, "Ukeshartam le'ot al yadekha" — "You shall bind them as a sign upon your arm." The Sages explain that this means the hand opposite the writing hand. That's the basic rule. If you write with your right hand, the Tefillin go on your left arm. If you write with your left hand, they go on your right. This is how the Shulhan Aruch rules in Orah Haim 27:6. The Mishnah Berura follows the same position. The weaker hand is used for Tefillin, because the act of binding represents control and submission of our actions to Hashem — and this symbolism applies specifically to the hand that is not dominant. What If a Person Writes with One Hand but Does Most Tasks with the Other? This comes up a lot. Let's say someone writes with his left hand but eats, throws, and does everything else with his right. Which is his dominant hand? The general rule is that writing is the primary indicator of dominance. If a person writes with his left hand, he is considered left-handed for Halachic purposes — and he should wear Tefillin on his right arm. Even if he does many other things with his right hand, the fact that he writes with his left gives it priority in Halacha. That said, if there's real uncertainty — someone is truly mixed or doesn't feel natural with either — he should speak to a Rav. But in most cases, the writing hand decides the matter. What If a Person Is Ambidextrous? In a rare case where someone uses both hands equally and writes comfortably with both, the Halacha treats him like a righty, meaning the Tefillin should be worn on the left arm. That's the ruling in most Poskim. In cases of doubt, we follow rov — the majority — and most people are right-handed. What If a Person Loses Use of His Dominant Hand? If a person becomes permanently unable to use his dominant hand — due to stroke, nerve damage, or any other reason — and now functions primarily with the opposite hand, the Halachic ruling may change. That person is now treated as if his non-dominant hand has become dominant, and the Tefillin should be worn on the new weaker arm. I once had a case where a man lost full use of his right arm. He was born right-handed, but after an injury, he could no longer write, eat, or function with that arm. He was now doing everything with his left. In that case, we ruled that he was now a lefty and should put Tefillin on his right arm. If the condition is temporary, such as post-surgery or while recovering from an injury, the ruling stays as-is. But if the condition is permanent and the person's habits have shifted accordingly, the Halacha adapts. What If One Arm Has Been Amputated? If someone is missing one of his arms, this too affects how Tefillin is worn. - If a right-handed person has had his left arm amputated, then the usual placement of the Tefillin Shel Yad is impossible. - If there remains some muscle or upper-arm area, and the strap can be wrapped around it, the Tefillin may be placed there. - If nothing usable remains, the Tefillin Shel Yad cannot be worn — but the person should still wear the Tefillin Shel Rosh. This is a rare case, but one that arises. The general rule is that Tefillin must be placed on the upper arm in a specific position. If there's no limb, the Misva simply doesn't apply in that case — but one still fulfills the Misva of the Shel Rosh. Does This Apply Equally to Tefillin of Rabbenu Tam? Absolutely. Whether one is wearing Tefillin of Rashi, Rabbenu Tam, or both, the choice of arm follows the exact same rule. We don't differentiate based on which Tefillin you're wearing. The arm is chosen based on your dominant hand — period. Summary - Tefillin are worn on the weaker arm: left for righties, right for lefties. - The writing hand determines which arm is considered dominant. - Ambidextrous people are generally treated as right-handed and wear Tefillin on the left arm. - If a person permanently loses use of their dominant hand, the Halacha may shift and reclassify their status. - In cases of amputation, Tefillin are worn if possible on remaining muscle. If not, the Shel Rosh should be worn without the Shel Yad. - This applies equally to both Rashi and Rabbenu Tam Tefillin.