You may not sow your vineyard with a mixture of seeds, for then the [seeds'] growth and even the seed that you planted together with the [fruit] yield of the vineyard will become forbidden.

You may not plow with an ox and a donkey together.

You may not wear shatnez, [which is] wool and linen together.

-- Devarim 22:9-11

Classic Questions

Why may one not plow with an ox and a donkey? (v. 10)

Ramban: Because it would lead to the further prohibition of crossbreeding species (Vayikra 19:19). For the farmer will house the ox and the donkey together, and they will breed with each other.

To what extent may wool and linen not be mixed? (v. 11)

Rashi: If wool and linen are combed together, and spun into thread, and woven together into cloth, then it is Biblically forbidden [to wear a garment that is made from this cloth] (as quoted in Tur, Yoreh De'ah ch. 300).

Rabeinu Tam: Woolen thread and linen thread that were prepared separately will become Biblically prohibited if they are woven together as one cloth (Tosfos ibid.).

Rambam: When wool and linen are bound together in any way whatsoever, the product is prohibited by the Torah (Laws of Forbidden Mixtures 10:2).

The Rebbe's Teachings

Forbidden Mixtures (v. 9-11)

The three prohibited mixtures mentioned in verses 9-11 share a similar theme, but a key distinction between them concerns the extent of the mixture. With the mixing of seeds (v. 9), the result is a new entity of a single, forbidden crop, which grows together and becomes harvested together as one. However, in the case of plowing with an ox and a donkey together (v. 10), no actual mixing results, for after the plowing is complete, the ox remains an ox and the donkey, a donkey.

We may therefore ask the question: Which of these two types of mixtures does the prohibition of shatnez (v. 11) most resemble?

Perhaps we could argue that this is the source of contention between Rashi and Rabeinu Tam. Rashi understands that shatnez most resembles the prohibition of mixed seeds, where two crops merge into one. Therefore, he writes that in order for a garment to become shatnez, the fibers must be totally mixed as one through all the stages: combing, spinning and weaving.

However, Rabeinu Tam understands that shatnez resembles the prohibition of plowing with an ox and a donkey together, where the two elements retain their individual identity. Therefore, he rules that woolen thread and linen thread that were prepared separately will become Biblically prohibited if they are woven together as one cloth.

Rabeinu Tam's reasoning appears to be the more obvious of the two, since the Torah actually places the prohibition of shatnez (v. 11) directly after the prohibition of plowing with an ox and donkey together (v. 10), suggesting that they are linked. Furthermore, these two verses constitute one single paragraph in the Hebrew text of the Torah, which stresses their connection further, whereas the prohibition of sowing mixed seeds (v. 9) is recorded separately, in the previous paragraph, suggesting that it is of a different nature.

Rashi agrees that the inclusion of the two prohibitions (shatnez and plowing with an ox and donkey) in one paragraph suggests that they are of a similar nature. Where he differed with Rabeinu Tam is in his understanding of why plowing with two different animals is prohibited. Rashi follows the reasoning of Ramban, that the Torah prohibits plowing with an ox and donkey together because it would lead to the further prohibition of crossbreeding species (Vayikra 19:19). Therefore, when Rashi saw that the Torah placed the two prohibitions of shatnez and plowing with two different animals side by side in the same paragraph, he concluded that all forbidden mixtures are fundamentally based on the same idea—making a new entity from the mixture. And just as the Torah prohibits plowing with two species together, for fear they will merge into a new entity (through cross-breeding), so too we are prohibited to wear a garment of wool and linen fibers that have merged into a new entity, i.e., that have bound together during all three processes of combing, spinning and weaving.

The View of Rambam

Rambam rules that if wool and linen are combined in any way, the result is shatnez. For example, if wool and linen raw fibers are combed together (and not spun or woven) and then pressed into felt, it would be shatnez according to Rambam.

Thus, Rambam takes a position which partially accepts the arguments of both Rashi and Rabeinu Tam. Rashi holds that shatnez is the creation of a new entity, and that therefore the prohibition applies only when the wool and linen were combined at all stages of the process (combing, spinning and weaving). Rabeinu Tam prohibits only the act of combining wool and linen after they have been processed (combed, etc.) separately. Rambam defines shatnez as a combination even in the formative stages (like Rashi), but deems one act of combination sufficient (like Rabeinu Tam).1

(Based on Likutei Sichos vol. 34, p. 123ff.)