Although the Torah prohibits sha’atnez, it requires wool and linen to be combined in two mitzvot involving clothing: the priestly garments and tzitzit.
During the Temple service, every kohen wore four garments: a tunic, breeches, and a turban, all made of white linen, and a sash woven from both wool and linen. The sash was made from four threads: one of white linen and three of dyed wool – tekhelet (sky blue), argaman (purple), and tola’at shani (crimson). The dyed threads were made of wool because wool absorbs dye well. The Kohen Gadol wore four additional garments: the robe, the efod (apron-like garment), the ḥoshen (breastplate), and the tzitz (frontlet). The Torah requires wool and linen to be combined in the efod and the ḥoshen. Kohanim were permitted to wear these sha’atnez garments only while serving in the Temple. Upon leaving the Temple, they had to remove the priestly garments to avoid violating the prohibition of sha’atnez.[10]
Regarding tzitzit, the Torah states: “You shall not wear sha’atnez, wool and linen together. You shall make tassels for yourself on the four corners of the garment with which you cover yourself” (Devarim 22:11–12). From the juxtaposition of these verses, the Sages derived that sha’atnez is permitted for the mitzva of tzitzit. The mitzva requires the tassels placed on the corners of the garment to contain both white and tekhelet threads. Since tekhelet threads were made of wool, attaching them to a linen garment creates sha’atnez; nevertheless, the Torah commands it. This teaches a general principle: whenever a positive mitzva conflicts with a prohibition, the positive mitzva takes precedence and the prohibition is set aside (Yevamot 4a–b).
The Sages nevertheless decreed that woolen tekhelet threads not be attached to a linen garment and that only white tzitzit threads be used. They were concerned that one might wear the garment at night, when one is exempt from tzitzit, and thereby violate the prohibition of sha’atnez (Menaḥot 40a–b; Shabbat 25b; MT, Laws of Tzitzit 3:6–7).[11]
The Gemara disagrees as to whether the sash of an ordinary kohen was sha’atnez like that of the Kohen Gadol (Yoma 6a, 12a, 69a). The halakha follows the view that it was (MT, Laws of the Temple Vessels 8:1–2). According to Rambam, the kohanim were permitted to wear the sash only while performing the Temple service (ibid. 8:11; MT, Laws of Kilayim 10:32). Other authorities permit them to wear it for as long as they remained in the Temple (Ra’avad on MT, Laws of the Temple Vessels 8:11; Tosafot, Menaḥot 41a; Rosh; Sha’agat Aryeh, old edition, §§29–30).
[11]. As explained above, the Sages derived from the juxtaposition of the verses that the mitzva of tzitzit overrides the prohibition of sha’atnez, permitting linen threads to be placed on a wool garment and wool threads on a linen garment (Yevamot 4a–b). Rav Yehuda rules likewise (Menaḥot 39b). The Gemara concludes, however, in accordance with Reish Lakish: “Whenever you find a positive commandment and a prohibition, if you can fulfill both, that is preferable; if not, let the positive commandment override the prohibition” (Menaḥot 40a). On this basis, Rambam rules that on a wool garment, the white threads must also be wool and may not be linen.
Others maintain that there is no contradiction between Rav Yehuda and Reish Lakish (Tosafot, Yevamot 4b, s.v. de-afilu; Tur). Sha’atnez in tzitzit follows a special rule: once the mitzva is properly fulfilled with tekhelet, sha’atnez is permitted even when not strictly necessary. Thus, white woolen threads may also be attached to a linen garment. Rashba and Ritva explain Reish Lakish differently: if the owner of a linen garment can obtain white linen threads, he must use them rather than resort unnecessarily to wool. If he cannot obtain them, however, even though they are generally available, he may use white woolen threads, as Shmuel and Rav Yehuda rule. One view in Tosafot maintains that the Amoraim do not disagree at all: by Torah law, sha’atnez is entirely permitted in tzitzit, while rabbinic law permits it only when necessary.
Although by Torah law the mitzva of tzitzit overrides the prohibition of kilayim, the people of Jerusalem did not attach tekhelet to linen garments. Rabbi explained that the Sages enacted this decree “because they are not proficient,” lest people come to use kilayim when no mitzva applies (Menaḥot 40a). According to Rif, Rashi, Rambam, Ramban, Rashba, and R. Yeruḥam, the decree prohibited woolen tekhelet threads but permitted white linen threads. Rav Hai Gaon, Rav Amram Gaon, Rabbeinu Tam, Ittur, Semag, and Semak maintain that the Sages prohibited attaching any tzitzit to a linen garment, lest one attach tekhelet and violate the prohibition. In practice, SA and Rema rule that ideally one should take into account the view of Rabbeinu Tam and those who follow him and avoid making a linen tallit. A person who has no wool tallit, however, should fulfill the mitzva with a linen tallit and linen tzitzit, in accordance with Rif and those who follow him (SA OḤ 9:6).
