On which arm is the Tefillin Shel Yad to be worn on?[1]

A. The general rule & Righty versus Lefty:

The weaker and non-writing hand:[2] The hand Tefillin is to be wrapped on the weaker and more frail of ones two hands, as the verse[3] states “Al Yadkah” and the Sages expounded that this word is to be read as “Yad Keiha” which is one’s weaker and more frail hand.[4] In addition, the Tefillin is to be wrapped using the hand which one writes with, and is thus wrapped onto the hand that one does not use to write.[5] Accordingly, the hand onto which the hand Tefillin is to be wrapped on is dependent on one’s right or left handedness, as will now be explained.

Righty-The law for one who is right-handed:[6] [If one is right-handed] the hand Tefillin is to be wrapped on one’s left arm.[7] [Practically, 90% of the world’s population is made up of right-handed people[8], and hence the vast majority of the world wears their Tefillin on their left hand. If he wore the Tefillin on his right hand, then he does not fulfill his obligation.[9]]

Lefty-The law for one who is Left-handed:[10] One who is left-handed, and performs all of this work with his left hand, is to wear his Tefillin on his right arm.[11] [If he wore the Tefillin on his left hand, then he does not fulfill his obligation.[12]]   

B. The law by different forms of ambidextrous:[13]

The law if one writes with both hands:[14] If one writes using both hands, then he is to wrap the Tefillin onto his left arm, as does one who is right-handed. This applies even if he does majority of his actions with his left hand. [However, some Poskim[15] rule that if he also does majority of his actions with his left hand, then he is to put the Tefillin on his right hand like a lefty. Nevertheless, after Davening he is to place the Tefillin also on his left hand, in order to suspect for the first opinion.]

Ambidextrous-The law if one does all of his actions equally with both hands:[16] It goes without saying that if one is ambidextrous and is able to use both hands equally for all of his actions [and is thus not defined as neither a righty or lefty] nevertheless, he is to wrap the Tefillin onto his left arm, as does one who is right-handed.

The law if one writes with his right hand but does all his actions with his left hand:[17] One who writes with his right hand is to wear the Tefillin on his left arm even if he does all his other actions with his left hand.[18] [However, some Poskim[19] rule that in such a case he is to wear the Tefillin on his right hand, like a lefty.[20] Accordingly, some Poskim[21] conclude that in such a case he is to put the Tefillin onto both arms due to doubt. This means that he is to first wear it on one arm and afterwards take it off and wear it on the other arm.[22] Practically, there is no clear arbitration in this dispute.[23] Nonetheless, the widespread custom is not to be stringent like the latter opinion, and rather the custom is to only wear the Tefillin on the left arm, similar to a righty.[24] However, some write that it is proper in such a case for the person to train his right arm to also perform some actions, and hence be considered a righty according to all.[25] In all cases, one is the contact a Rav for a final arbitration on this matter.[26]]

The law if one writes with his left hand but does all his actions with his right hand:[27] One who writes with his left hand is to wear the Tefillin on his right arm even if he does all his other actions with his right hand.[28] This however only applies if one writes with his left hand from birth. If, however, he was born writing with his right hand and trained himself to write with his left hand, then he is to wear the Tefillin on his left hand, as will be explained below. [However, some Poskim[29] rule that in such a case he is to wear the Tefillin on his left hand, like a righty.[30] Accordingly, some[31] conclude that in such a case he is to put the Tefillin onto both arms, due to doubt. He is to wear the Tefillin on one arm during Davening, and after Davening he is to don the Tefillin on the other hand.[32] Practically, there is no clear arbitration in this dispute.[33] Nonetheless, the custom is not to be stringent like the latter opinion, and the custom is to rather only wear the Tefillin on the right arm, just like a lefty.[34] However, some write that it is proper in such a case for the person to train his right arm to also write, and hence be considered a righty according to all.[35] In all cases one is the contact a Rav for a final arbitration on this matter.[36]]

The law by one who was born a righty and trained himself to become a lefty:[37] The above law that one who writes with his left hand puts on his Tefillin on his right arm applies even if he does majority of his actions with his right arm, only applies if one writes with his left hand from birth. However, if he was born a righty and would thus write only with his right hand, and only later trained himself to write with his left hand, then he is to wear the Tefillin on his left hand, like a righty, if he does the rest of his actions with his right hand.[38] However, if he trained himself to do all of his actions with his left hand [including writing], then [if he does not also write with his right hand] he is to wear the Tefillin on his right hand like a lefty.[39] [However, if he also writes with his right hand then he is to wear the Tefillin on his left hand, just like a righty, as explained above.]

The law by one who was born a lefty and trained himself to become a righty:[40] One who was born left handed  and trained himself to become right handed, and hence writes and does all his actions with his right hand, is to put on his Tefillin on his left hand just like a righty. [However, if he only trained himself to write with his right hand then he remains a lefty although is to be stringent to wear the Tefillin both hands, wearing it on the left hand prior to Davening and on the left-hand during Davening.[41]]  

 

Summary: The Tefillin is to always be placed on the left hand unless: 1.       One writes with only his left hand from birth even if he does all his other actions with his right. [However, some are stringent in such a case to also wear the Tefillin on the left hand. Likewise, if one writes only with his right hand and performs all of his actions with his left hand, stringent to also wear the Tefillin  on the right hand.] 2.       One trained himself after birth to do all his actions with his left hand, including writing, and does not write at all with his right hand. In any of above cases if either a) one writes also with his right hand or b) writes only with his left hand but he was not born this way [and rather trained himself to do so], and he does all his other action with his right hand, then he is to place the Tefillin on his left hand.    Q&A Should a lefty try to train himself to become a righty in order so he can wear the filling on his left hand?[42] Some Poskim[43] encourage one to do. Other Poskim[44], however, discourage one from doing so. Practically, one is not to do so without first discussing the matter with his rabbi and doctor.   How is one who is left-handed to wear Tefillin of one who is right-handed [or vice versa], if his own Tefillin is not available?[45] Introduction: The only difference between the Tefillin worn by one who is left-handed versus one who was right-handed, is the positioning of the knot of the Yud which is adjacent to the Ketzitza of the hand Tefillin. It is customary for this knot to face inwards towards the heart[46], and hence this knot is adjacent to different sides of the Ketzitza by a righty versus a lefty’s Tefillin. Accordingly, one who wears the Tefillin of a righty on his right arm ends up having the knot face away from his heart, and the question is thus asked as to what he is to do. The same question applies vice versa, if a right-handed person only has a left handed person’s Tefillin available. The law: If the only available Tefillin for a lefty is one of a person who is right handed, then some Poskim[47] rule that one is to undo the knot of the Yud and retie it on the other side, so that when he places it on, the knot faces inwards. If this is not possible, then one is to place the Tefillin on his right arm in the reverse order, having the Titura face towards the elbow, in order so the knot be facing inwards.[48] Practically, many even initially follow this second option.[49] [However, one should not place it on normally, thus causing the knot to be on the outer side.[50]]

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[1] Admur 27:1, 9-10; Ketzos Hashulchan 8:13; See Tzemach Tzedek O.C. 4, 5, 12 in great length; Kaf Hachaim 27:317; Piskeiy Teshuvos 27:12-15; Nesivim Bisidei Hashlichus 1:44; Sefer Dinei Iter chapter 5

[2] Background: The Gemara in Menachos 36b-37a discusses which arm one is to wear the arm Tefillin on, and while there is consensus that it should be worn on the left arm, the reason behind this is debated. 1) The first approach in the Gemara ibid is that based on a revelation of verses we see that the term “Yad/hand” in scripture refers to the left hand, and hence since the verse explicitly states to wear the Tefillin on “Yadcha” it is considered to explicitly refer to the left hand. 2) The second approach in the Gemara, of Rav Yossi Hachoreim [see Rashi and Tosafus ibid for the source of this name], argues that we find in scripture that the term Yad can also refer to the right arm, and he therefore negates the above approach. Rather, he and Rebbe Nassan learn that the hand Tefillin is placed on the left arm based on the words “Ukeshartem Ukesavtem” which teaches us that just as one writes with his right hand, so too he must tie with his right hand, and from the fact that the tying is with ones right hand one can deduce that the tying of the Tefillin Shel Yad must be done on the left hand, as he must use his writing hand for tying the Tefillin onto the opposite hand. 3) Rav Ashi offers a third approach and explains that the word Yadcha written in scripture is written with an anomaly, as the Hei is read as a weak Hei, which hints to the fact that one is to don the hand Tefillin on the weaker hand, which is the left hand. There are several practical ramifications between the reasons, such as onto which hand a lefty is to wear his Tefillin, and to if one’s weaker hand is his right hand, but he writes with his right hand, or vice versa, as according to the first and second reason he should wear the Tefillin on his left hand, while accoridng to the third reason he should wear it on his right hand. [See Tosafus Menachos 37a “Mah Kesiva”] Admur 27:1 records the 3^rd reason, while in 27:9 he records the second reason. The Michaber 27:6 records the 2^nd and 3^rd reason as two dissenting opinions; See Tzemach Tzedek O.C. 4 for a full analysis on this subject and the opinion of the various Poskim; The following Halacha will analyze and clarify the final rulings on this subject

[3] Shemos 13:16

[4] Admur 27:1; 1^st opinion in Michaber 27:6; Rav Ashi Menachos 37a

[5] Admur 27:9; 2^nd opinion in Michaber 27:6; Taz 27:7; Hagahos Semak 153:8; Rav Yossi Hachoreim and Rav Rebbe Nassan in Menachos 37a

The reason: As the verse [Devarim 6:8] states “Ukeshartem Ukesavtem” which teaches us that just as one writes with his right hand, so too he must tie with his right hand, and from the fact that the tying is with ones right hand one can deduce that the tying of the Tefillin Shel Yad must be done on the left hand, as he must use his writing hand for tying the Tefillin onto the opposite hand. [Admur ibid; Taz ibid; Menachos ibid]

[6] Admur 27:1; Siddur Admur; Michaber 27:1; Menachos 36b

[7] The reason: As the verse states “Al Yadkah” and the Sages expounded that this word is to be read as “Yad Keiha” which is one’s left hand which is weaker and frailer. [Admur ibid; Taz 27:1; Levush 27; Rav Ashi in Menachos 37a] Alternatively, the reason is because the Tefillin is to be wrapped with one’s writing hand onto the opposite arm, which is one’s weaker hand. [Admur 27:9; See general rule and background in footnotes for other reasons offered. Vetzaruch Iyun why in this Halacha 27:1 Admur makes no mention of the other reason of Rebbe Nassan, despite bringing it in 27:9.] Thus, if one writes with his right hand then he is to place the Tefillin on his left arm, using his right hand to wrap it onto his left arm. If one writes with his left hand then he is to don the Tefillin on his right hand using his left hand to wrap it.

[8] https://www.worldatlas.com/articles/what-percentage-of-the-world-population-are-left-handed.html

[9] All Poskim who invalidate a lefty who wore on his left hand; Tzemach Tzedek O.C. 4:2 “If he wears it on his right hand he does not Fulfill his obligation at all”

[10] Admur 27:9 “…On his left hand which is the right hand of all other people”; Michaber 27:6; Tur 27; Semak 153; Sefer Hateruma 213; Menachos 37a; Tzemach Tzedek O.C. 4:1 that so applies even according to Riy, unlike Mordechai

Other opinions: Some Poskim rule that even a lefty is to wear his Tefillin on his right arm just as everyone else. [Implication of Tana Kama Menachos ibid; Meiri Shabbos 104a in understanding of Rebbe Yitzchak in Menachos 37b; Mordechai end of Hilchos Tefillin according to Riy and Tana Kama, brought in Tzemach Tzedek O.C. 4:1; Mishkanos Yaakov 33 in name of Semg and Semak in opinion of Tana Kama, brought and negated in Tzemach tzedek ibid 4:7; Shalmei Tzibur in name of Zer Zahav of Mahari Tzemach based on Kabalah, brought in Shaareiy Teshuvah 27:7; Sefer Nagid Umitzvah; The following Poskim record this opinion: Yifei Laleiv 27:3; Ben Ish Chaiy Chayeh Sarah 7] Accordingly, some Poskim conclude that a lefty is to put on his Tefillin on both arms, first on the right arm as required according to Halacha, and then on the left arm as required according to Kabbalah. [Chesed Lealafim 27:5; Ben Ish Chaiy ibid; Rav Poalim 2:9; Kaf Hachaim ibid; Divrei Yatziv 1:15] Practically, the custom is not like this opinion, and hence the left only puts his Tefillin on his right arm. [Chelkas Yaakov 4:42; Igros Moshe 4:11; Az Nidbaru 14:33] See Kaf Hachaim 27:31; Minchas Yitzchak 10:4; Piskeiy Teshuvos 27:12 and footnote 99 for negation of this ruling

[11] The reason: As the Tefillin is to be wrapped with one’s writing hand onto the opposite arm, which is one’s weaker hand. [Admur ibid] Alternatively, the reason is because the verse states “Al Yadkah” and the Sages expounded that this word is to be read as “Yad Keiha” which is one’s left hand which is weaker and frailer. [Admur 27:1; Taz 27:1; Levush 27; Rav Ashi in Menachos 37a; See general rule and background in footnotes for other reasons offered.] Thus, if one writes with his left hand then he is to don the Tefillin on his right hand using his left hand to wrap it.

[12] Chut Hashani 167; Beir Heiytiv 27:11; M”B 27:24; Biur Halacha 27:6 “Maniach”; Maharsham 2:240; See Piskeiy Teshuvos 27:12

Other opinions: Some Poskim rule that if a lefty wore the Tefillin on his left hand then Bedieved he fulfills his obligation. [Shaareiy Teshuvah 27:11 in implication of Beis Yosef 27 in name of Baal Haitur; Artzos Hachaim 27:34; Divrei Yatziv 1:15; Birchos Shamayim 1:1; All Poskim in previous footnotes in other opinions who rule that even initially he used to put it on his left arm]  

[13] See Admur 27:1, 9-10; Ketzos Hashulchan 8:13; See Tzemach Tzedek O.C. 4, 5, 12 in great length; Kaf Hachaim 27:317; Miasef Lechol Hamachanos 27; Piskeiy Teshuvos 27:12-15; Nesivim Bisidei Hashlichus 1:44; Sefer Dinei Iter chapter 5

[14] Admur 27:9 “Even if he also writes with his left hand, since he writes also with his right hand, therefore he needs to tie his Tefillin using that hand [i.e. right] on the opposite hand.”; M”A 27:10 in implication of Semak; Ketzos Hashulchan 8:13; See Piskeiy Teshuvos 27:13  

[15] All Poskim who rule to follow ones weaker hand versus ones writing hand, brought in coming footnotes; Conclusion of Tzemach Tzedek O.C. 4:2 and 12:3 that even according to Tosafus it is possible that if he does all of his actions with his left hand and also writes with his left hand that he is viewed as a lefty, and so certainly applies according to the Sefer Hateruma and Rosh, and therefore the main approach is for him to put on the Tefillin onto his right hand like a lefty although in order to suspect for the first opinion one should also be stringent to put it on his left hand after Davening

[16] Admur 27:9; Michaber 27:6; Tur 27; Ketzos Hashulchan 8:13; See Piskeiy Teshuvos 27:13 for the exact definition of one who does all his actions with both hands; See Piskeiy Teshuvos 27:13 for definition of one who uses both hands equally    

[17] Admur 27:9; Rama 27:6 that so is custom; 2^nd Opinion in Michaber 27:6 [Kneses Hagedola Kelalei Haposkim 62 writes that the main opinion always follows the 2^nd opinion]; Rav Yechiel of Paris brought in Hagahos Semak 153:8 and Tur 27; M”A 27:10; Bach 27; Taz 27; Elya Raba 27; M”B 27; Kaf Hachaim 27:31 [as so rules Michaber like 2^nd opinion and so rules Arizal who is final arbitrator]; Ketzos Hashulchan 8:13; Shevet Halevi 9:14; Yabia Omer 6:2; 9:108; Shoel Vinishal 1:3; See Kaf Hachaim 27:31; Piskeiy Teshuvos 27:14

[18] The reason: As the verse [Devarim 6:8] states “Ukeshartem Ukesavtem” which teaches us that just as one writes with his right hand, so too he must tie with his right hand, and from the fact that the tying is with ones right hand one can deduce that the tying of the Tefillin Shel Yad must be done on the left hand, as he must use his writing hand for tying the Tefillin onto the opposite hand. [Admur ibid; Taz 27:7; Semak ibid; 2^nd reason in Menachos 37a]

[19] 1^st opinion in Michaber 27:6; Sefer Hateruma 213; Rosh Tefillin 18; Biur Hagr”a 27:17; Tzemach Tzedek O.C. 4:2 that so applies according to Rashi and Tosafus according to one opinion in Gemara, and so is opinion of Riy and Mordechai and Rabbeinu Yerucham

[20] The reason: As the verse [Shemos 13:16] states “Al Yadkah” and the Sages expounded that this word is to be read as “Yad Keiha” which is one’s weaker and more frail hand. [Michaber ibid; See Admur 27:1; Rav Ashi Menachos 37a]

[21] Tzemach Tzedek O.C. 4:2 and 12:3; Chesed Lealafim 27:5; Kaf Hachaim 27:31 that one who is stringent to wear on the opposite arm after Davening is blessed; Opinion of Rav Yaakov Landau, brought in Yagdil Torah 38:36; Sefer Dinei Iter 5:15; See Igros Kodesh 11:148 regarding that some wear also after Davening on other arm

[22] Tzemach Tzedek ibid; Kaf Hachaim ibid; Rav Yaakov Landau writes to first wear on the left-hand during Davening and then on the right hand after Davening, however, from the Tzemach Tzedek it is implied to first wear on the right-hand during Davening and only then on the left after Davening Vetzaruch Iyun

The blessing: One is to say blessing the first time he puts it on irrelevant of which hand he chooses. we do not apply here the rule of Safek Brachos Lihakel, as in any event the blessing also covers the head Tefillin. [See Tzemach Tzedek 5:11; Igros Kodesh 11:148, printed in Shulchan Menachem 1:82]

Other opinions: Some Poskim rule that he is tow ear two hand Tefillin simultaneously during Davening. [Chesed Lealafim 27:5] Practically, one is not to do so due to Baal Tosif. [Yifei Laleiv ibid; Ben Ish Chaiy ibid; Kaf Hachaim ibid]

[23] Piskeiy Teshuvos 27:14; See Rabbanim in next footnote that there is likewise no tradition amongst the Chabad Rabbeim, or official Chabad custom, as to whether one is to follow Admur or the Tzemach Tzedek

[24] See Igros Moshe 4:11 that the custom is not to require one to be stringent to wear it on both hands; Yagdil Torah 38:36 that the custom is like Admur ibid to wear on left [So write the Alterer Rabbanim of Anash: Rav Gringlass that so he was ruled by Ziknei Rabbanei Anash; Rav Shnear Zlaman Gerelik that the custom is to follow Admur and not the Tzemach Tzedek, although he has received no Chabad tradition in this matter; Rav Alexander Yudsin to do only like Admur and that we have never seen or heard of anyone who puts it on both arms ; Rav Perlow that although he received no tradition, the custom of the world is to follow the writing hand as rules Admur; Rav Hillel Pezner writes that he did not receive a tradition in this, although agrees in the scenario asked like Admur; and so rule of Rabbanei Anash today: Rav Farkash, brought in Hiskashrus]; There is a Maaneh of the Rebbe to an individual regarding this matter, that one should follow Rabbanei, and Ziknei Rabbanei Anash, who rule like Admur ibid; See also Nesivim Bisidei Hashlichus 1:44

Other opinions of today’s Rabbanim and Poskim: See Piskeiy Teshuvos 27:14 that the above dispute is not arbitrated and that based on the Biur Halacha 27 “Vehachi Nahug” one should attempt to do like all opinions. Rav Yaakov Landau ibid and Sefer Dinei Iter 5:15 both conclude like Tzemach Tzedek to wear on both arms.

Analysis on Chabad ruling, custom, and opinion of Rebbe: See coming footnotes!

[25] Piskeiy Teshuvos 27:14

[26] See Igros Kodesh 11:148, printed in Shulchan Menachem 1:82 to ask Rabbanei Anash; Likewise, there is a Maaneh of the Rebbe to an individual regarding this matter, that one should follow Rabbanei, and Ziknei Rabbanei Anash, who rule like Admur ibid

[27] Admur 27:9; Rama 27:6 that so is the custom; 2^nd Opinion in Michaber 27:6 [Kneses Hagedola Kelalei Haposkim 62 and Kaf Hachaim 27:31 write that the main opinion always follows the 2^nd opinion]; M”A 27:10; Rav Yechiel of Paris brought in Hagahos Semak 153:8 and Tur 27; Taz 27; Elya Raba 27; M”B 27; Ketzos Hashulchan 8:13; Yabia Omer 6:2; 9:108; Shoel Vinishal 1:3; See Kaf Hachaim 27:31; Piskeiy Teshuvos 27:14

[28] The reason: As the verse [Devarim 6:8] states “Ukeshartem Ukesavtem” which teaches us that just as one writes with his right hand, so too he must tie with his right hand, and from the fact that the tying is with ones right hand one can deduce that the tying of the Tefillin Shel Yad must be done on the left hand, as he must use his writing hand for tying the Tefillin onto the opposite hand. [Admur ibid; Taz 27:7; Semak ibid; 2^nd reason in Menachos 37a]

[29] 1^st opinion in Michaber 27:6; Sefer Hateruma 213; Rosh Tefillin 18; Biur Hagr”a 27:17; Tzemach Tzedek O.C. 4:2 that so applies according to Rashi and Tosafus according to one opinion in Gemara, and so is opinion of Riy and Mordechai and Rabbeinu Yerucham; Bach 27, brought in M”A 27:10, that so applies according to all Poskim and this matter is not under debate; Tzemach Tzedek O.C. 4:2 that a) so applies even according to Rebbe Yechiel ibid and that b) so should be done according to the Michaber ibid who does not give an arbitration, and c) even the Darkei Moshe 27:4 writes that there is no set custom regarding this. And d) The main opinion follows the Bach ibid; To quote in his words: “Now, regarding The M”A ibid who ruled that one is to put it on his right arm like a lefty, with all due respect, his words are not correct at all and anyone who follows his words does not fulfill his obligation at all when he wears it on his right hand like a lefty he is rather to wear it on his left hand”; Mor Uketzia 27; Magen Giborim 27; Artzos Hachaim 27; Shoel Umeishiv Tinyana 2:58; 3:123; Aruch Hashulchan 27; Kaf Hachaim 27:31 [as so rules Mekubalim who are the final arbitrator of a debate, as well as because in any dispute one should always wear on left]; Igros Moshe 4:11; Cheshev Haeifod 1:103; See Piskeiy Teshuvos 27:12-15 for all opinions

[30] The reason: As the verse [Shemos 13:16] states “Al Yadkah” and the Sages expounded that this word is to be read as “Yad Keiha” which is one’s weaker and more frail hand. [Michaber ibid; See Admur 27:1; Rav Ashi Menachos 37a]

[31] Kaf Hachaim 27:31 that one who is stringent to wear on the opposite arm after Davening is blessed; See Piskeiy Teshuvos 27:14; Omitted from Tzemach Tzedek ibid, which implies that according to his opinion there is no need at all to be stringent and put it also on the right arm after Davening. [See Tzemach Tzedek ibid New Edition footnote 66]

[32] Kaf Hachaim ibid that first wear on left and then on right; See Igros Kodesh 11:148, printed in Shulchan Menachem 1:82, regarding the general idea to wear on other arm after Davening, although not in discussion of the above case

The blessing: One is to say blessing the first time he puts it on irrelevant of which hand he chooses. we do not apply here the rule of Safek Brachos Lihakel, as in any event the blessing also covers the head Tefillin. [See Tzemach Tzedek 5:11; Igros Kodesh 11:148, printed in Shulchan Menachem 1:82]

Other opinions: Some Poskim rule that he is tow ear two hand Tefillin simultaneously during Davening. [Chesed Lealafim 27:5] Practically, one is not to do so due to Baal Tosif. [Yifei Laleiv ibid; Ben Ish Chaiy ibid; Kaf Hachaim ibid]

[33] Piskeiy Teshuvos 27:14; See Rabbanim in next footnote that there is likewise no tradition amongst the Chabad Rabbeim, or official Chabad custom, as to whether one is to follow Admur or the Tzemach Tzedek

[34] Yagdil Torah 38:36 that the custom is like Admur ibid to follow the writing hand [So write the Alterer Rabbanim of Anash: Rav Gringlass that so he was ruled by Ziknei Rabbanei Anash regarding case of lefty writing with right hand; Rav Shnear Zlaman Gerelik that the custom is to follow Admur and not the Tzemach Tzedek, although he has received no Chabad tradition in this matter; Rav Alexander Yudsin to do only like Admur and that we have never seen or heard of anyone who puts it on both arms; Rav Perlow that although he received no tradition, the custom of the world is to follow the writing hand as rules Admur; and so rule of Rabbanei Anash today: Rav Farkash, brought in Hiskashrus]; There is a Maaneh of the Rebbe to an individual regarding this matter, that one should follow Rabbanei, and Ziknei Rabbanei Anash, who rule like Admur ibid, and certainly knew of the ruling of the Tzemach Tzedek and nevertheless ruled differently; See also Nesivim Bisidei Hashlichus 1:44

Other opinions of today’s Rabbanim and Poskim: See Piskeiy Teshuvos 27:14 that the above dispute is not arbitrated and that based on the Biur Halacha 27 “Vehachi Nahug” one should attempt to do like all opinions. Rav Yaakov Landau ibid concludes like Tzemach Tzedek to wear on both arms; Rav Ginzberg in Hiskashrus 554:16 and Sefer Dinei Iter 5:15 conclude based on Rebbe’s answer to Rav Shmuel Livitin to wear only on left arm as rules the Tzemach Tzedek

The Chabad ruling, custom, and opinion of Rebbe: The Alter Rebbe ibid rules that we always follow the writing hand versus the hand that is used for majority of one’s actions. Hence, one always wears the Tefillin on the hand that one does not use for writing. However, the Tzemach Tzedek ibid rules that we follow the majority of one’s actions versus writing, and hence if one does all his actions with his right then one is to put the Tefillin on his left hand. The above dispute is with regards to what’s is the main source for why one is to don the Tefillen on his left hand, is it due to “Yad Koh” the weaker hand [and thus one should place on his left in this scenario], or is it due to “Ukshartam Ucsavtam” [and thus one is to place them on his right]. This debate creates a great dilemma for Chabad Chassidim, as there’s an clarity as whether one should follow the Alter Rebbe’s ruling or that of the Tzemach Tzedek. In such a case, the Rebbe was accustomed to send the asker to ask Ziknei Rabbanei Anash. [See Igros Kodesh 11:148; Story with Rav Nasan Gurary brought below; Maaneh of Rebbe brought above] Practically, the testified Chabad custom by the Rabbanim is like the opinion of Admur and unlike the Tzemach Tzedek, and we were not even stringent to put it on the second arm after Davening, and so rule the majority of Chabad Rabbanim. Perhaps the reason for this is because the Tzemach Tzedek does not even record the ruling of his grandfather the Alter Rebbe, and if he would have seen his ruling he would have retracted from his conclusion. [See Yagdil Torah ibid] Nonetheless there does exist a testimony that the Rebbe once instructed a boy [Rav Nasan, Ben Rav S.Z. Gurary] in the above situation [is a righty who writes only with his left hand] to ask a Rav, and the Rav who was asked was Rav Shmuel Livitin. Rav Shmuel Livitin in turn asked the Rebbe and the Rebbe replied that he is to wear the Tefillin on the left hand as rules the Tzemach Tzedek. [See Dinei Iter 5:14]

[35] Os Chaim Vehsalom 27:8 in name of his grandfather; Cheshev Haeifod 1:103; 2:58; Az Nidbaru 14:32; Piskeiy Teshuvos 27:14 footnote 114

[36] See Igros Kodesh 11:148, printed in Shulchan Menachem 1:82 to ask Rabbanei Anash; Likewise, there is a Maaneh of the Rebbe to an individual regarding this matter, that one should follow Rabbanei, and Ziknei Rabbanei Anash

[37] Admur 27:10; M”A 27:9-10; Darkei Moshe 27 in name of Mordechai; Ketzos Hashulchan 8:13; See Halef Lecha Shlomo 11; Shoel Umeishiv Tinayan 2:58; Avnei Tzedek 3; Maharsham 3:299; Maharash Engel 3:13; Divrei Yoel 1:3; Divrei Yatziv 1:9; See Kaf Hachaim 27:31; Piskeiy Teshuvos 27:15

Other opinions: Some Poskim rule that it does not suffice for one to change his nature from a righty to a lefty, and if he was born a righty he used to always place the Tefillin on his left arm, even if he became accustomed to writing and doing all of his actions with his left arm. [Opinion in Mordechai, brought in M”A ibid; Manuscript of Levush, brought in Shevet Halevi 9:6; Teshuras Shaiy 2:85; See Piskeiy Teshuvos 27:15 footnotes 119-120]

[38] The reason: As in such a case the left hand still remains his weaker and more frail hand. [Admur ibid]

[39] The reason: As in such a case the right hand has now become his weaker and more frail hand. [Admur ibid]

[40] Admur and Poskim ibid Regarding a righty who trained himself to become a lefty and certainly this would apply in the opposite case; Halef Lecha Shlomo 11; Shoel Umeishiv Tinayan 2:58; Avnei Tzedek 3; Maharsham 3:299; Maharash Engel 3:13; Divrei Yoel 1:3; Divrei Yatziv 1:9; See Piskeiy Teshuvos 27:15

[41] Tzemach Tzedek 12:3

[42] See Piskeiy Teshuvos 27:15

[43] Halef Lecha Shlomo 11; Shoel Umeishiv Tinayan 2:58; Avnei Tzedek 3; Maharsham 3:299; Maharash Engel 3:13; Divrei Yoel 1:3; Divrei Yatziv 1:9

[44] Shevet Halevi 9:6; Teshuras Shaiy 2:85; See Piskeiy Teshuvos 27:15 footnotes 119-120

[45] See Piskeiy Teshuvos 27:5

[46] Admur 27:4; Michaber 27:2

[47] Nachlas Shiva 41; Kitzur SHU”A 10:7; Biur Halacha 27:3 “Haminhag Hanachon” in name of Chayeh Adam

Other opinions: Some Poskim rule that one is not to switch the knot of the Yud and is rather to always put the Tefillin on in the reverse order, as explained next. [Shvus Yaakov 1:3; Omitted from majority of Poskim in next footnote]

[48] Shvus Yaakov 1:3; Beir Heiytiv 27:10; Machatzis Hashekel 27:3; Yeshuos Yaakov 27:4; Artzos Hachaim 27:3; Aruch Hashulchan 27:17; Kaf Hachaim 27:11 and 27; Kitzur SHU”A ibid; Biur Halacha 27:3 “Haminhag Hanachon”; Kaf Hachaim 27:31; Yagdil Torah N.Y. 6:51; Hiskashrus 430:16; Shevach Yakar p. 73; Dinei Iter 5:6; See Nesivim Bisidei Hashlichus p. 45

[49] See Piskeiy Teshuvos ibid footnote 27

[50] The reason: Although both the wearing of the Tefillin in a way that it’s knot faces the heart and that it’s Mabarta faces the upper part of the shoulder is a mere good custom and not obligatory [See Admur and Michaber ibid], nonetheless one with the Tefillin of a person who wears it on the opposite arm should always choose to wear it in a way that the Mabarta is towards the elbow rather than have the knot face away from the heart. The reason for this is because the custom of wearing the knot of the Yud towards one’s heart is of greater importance than having the Mabarta facing the shoulder. [Se Biur Halacha ibid in name of Gra 27:7 and 9 that having the Yud face the heart is a Talmudic requirement as opposed to a mere custom]   

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