Halakhah zu Wajikra 11:32

Vessels and utensils are subject to defilement whereas structures or objects attached to the ground are not subject to defilement. The distinction lies in the fact that vessels and utensils are movable and can be transported from place to place whereas objects attached to the ground are immobile. Inordinately large objects may be immovable even if they are not attached to the ground. For purposes of the regulations governing defilement, objects are classified as vessels or utensils only if they are comparable to the "sack" described in Leviticus 11:32. According to rabbinic exegesis, the term "sack" serves as the paradigm for all vessels subject to defilement. The nature of a sack is that it can be transported "[when] full as well as [when] empty." Accordingly, only utensils that are not too heavy to be transported even when full are susceptible to defilement; gargantuan vessels that are not movable when full are treated as though they are rooted to the ground even when they are empty and hence cannot become defiled. The Mishnah, Oholot 8:3, declares that any utensil that holds forty se'ah is, by definition, too large to become defiled. The Mishnah further declares that since such utensils cannot become defiled they can also serve as an interposition preventing defilement from ascending ad coelum. Such an oversized utensil is termed a keli ha-ba be-middah. The dimensions of an airplane certainly seem to place it within that category.

4. Most significantly, the rule regarding keli ha-ba be-middah applies only to implements made of wood or leather and to articles of clothing that are enumerated together with the "sack" in Leviticus 11:32 as subject to defilement. However, metal utensils that are not mentioned in that verse are susceptible to defilement regardless of size.³³See Kelim 15:1 and Oholot 8:1. The definition of "metal" for this purpose will be addressed in a subsequent section.

Rabbi Silber takes issue with the position of both Rabbi Feinstein and Rabbi Frank and maintains that garments made of synthetic material require zizit no less than those made of natural fibers. He recognizes no distinction between garments made of synthetic thread and those cut directly from sheets of synthetic material.⁸This is also the position of Rabbi Y. E. Henkin, Am ha-Torah, no. 10, p.7. Rabbi Henkin offers a somewhat different explanation for the exclusion of leather from the obligation of ẓiẓit. The arguments of those who disagree, Rabbi Silber points out, are based primarily on the phraseology of the Levush who states that a "begged," by definition, must be made of woven material. Rabbi Silber cites Mishnah Berurah 10:11 which omits any reference to weaving in citing Levush. According to Rabbi Silber, "weaving" is not a necessary condition of what constitutes a begged but is simply a generalization used to exclude materials which do not constitute a begged. Leather is exempt, argues Rabbi Silber, because by its nature it does not generate warmth. Since it is not generally used for the making of clothing it is not deemed to be a "begged" even if it is fashioned into an article of clothing. This is so even if the leather is first cut into strips and then woven into a garment. That leather is not considered to be a begged is manifest from the phrase "a garment or leather" (Leviticus 11:32). Reference to a "a garment (begged) or leather" as separate entities demonstrates that leather, by definition, is not deemed to be a begged. Since synthetic fibers do provide warmth and are commonly used in the manufacture of clothing, a garment made of synthetic material, argues Rabbi Silber, should be considered a begged and such a garment requires zizit if it is four-cornered in shape. Furthermore, argues Rabbi Silber, since synthetic cloth is manufactured by a process which causes separate particles to adhere to one another, this process is comparable to weaving cloth out of individual strands of thread. Such materials are significantly different from leather which comes into being as a single entity. The term "woven" as used by Levush, argues Rabbi Silber, is intended simply to exclude that which is fashioned from a single piece, e.g., leather. According to Rabbi Silber, nylon or polyester may be used in the making of a tallit katan.