The Melakha of Kosheir
The melakha of kosheir is loosely defined as fastening two items through use of a "tying material," such as a rope. The examples cited by the gemara in Shabbat (112-113) include fastening animals to stalls, boats to piers, and buckets to wells. In this shiur, we will assess the nature of the melakha.
Presumably, the prohibition entails fastening two items together. Accordingly, the type of knot is less significant than the solidity of the fastening. If so, this melakha would be very similar to the melakha of tofer, which prohibits weaving garments and, by extension, any other form of fusing two items. Many question the difference between these two melakhot. Some claim that kosheir applies when the fastening can be easily reversed (by untying the knot, itself forbidden on Shabbat as the melakha of matir), whereas reversing the effect of tofer would demand destroying the newly fused item.
If this basic definition were true, the only parameter governing the prohibition should be the strength of the knot. In fact, the gemara in Shabbat (74b) indicates that the prohibition is dependent upon this strength – or, as the gemara terms it, the level of kesher shel kayama (permanence) that was generated. Many Rishonim (including Rashi and Tosafot) claim that this variable alone determines whether a knot is Biblically forbidden, Rabbinically forbidden, or completely permissible.
However, another gemara in Shabbat (112a) appears to differentiate between knots fastened by ordinary people and those made by professional tradesmen (ma'aseh uman). Many Rishonim (Rabbenu Chananel, the Rif, and the Rambam) claim that a knot is only Biblically forbidden if it is professionally manufactured and will last for an extended period. Evidently, these Rishonim defined the prohibition very differently from our original assertion. Kosheir is not merely fastening two items through a rope or the like. The very act of creating a "knot" for any reason is forbidden. Although knots are typically employed for fastening, that is not always the case. A knot also prevents something from unwinding, creates tautness in a rope, and can serve multiple other functions. In fact, a knot does not actually fasten to an item; it merely prevents a rope from slipping through a ring or hook. In reality, the item is fastened to the ring. According to these Rishonim, creating a formal knot is forbidden, and only professional knots are Biblically prohibited.
Even Rashi and Tosafot – who claimed that the knot's strength is the only determinant – may agree that the melakha is not defined as fastening two items, but rather as creating a knot. Nevertheless, they did not employ the variable of ma'aseh uman, the level of professional manufacture, to determine the identity of a knot. Only its long-term durability determines the identity of the knot and the level of the prohibition.
This approach to kosheir which views the melakha as crating a knot and not merely fastening items appears to underwrite an interesting statement of the Mordechai in the beginning of Chullin. He claims that tying the knot of tefillin would be prohibited on Shabbat even according to the opinion that the knot should be re-crafted on a daily basis (see Rabbenu Eliyahu in Tosafot, Menachot 36a). Even though the tefillin knot is not a kesher shel kayama (since it is recrafted daily), it is still forbidden to create it on Shabbat because the Torah refers to this knot as a "kesher.” Why should the Torah's formal designation of tefillin as a kesher prohibit a knot that is only temporary? If the melakha of kosheir is defined solely as fastening, the formal nomenclature should be irrelevant. If, however, the prohibition is defined as manufacturing a "knot," the formal designation is relevant. Common knots are defined solely based on their durability, or, possibly on whether they are professional knots. Torah-recognized knots that possess halakhic function are considered formal knots even if temporary.
This question likely affects whether the prohibition includes knots that do not actually fasten two items. Would tying a string or rope together be a violation of this melakha? The Avnei Nezer (180:1) addresses this issue and attempts to prove that it does violate the prohibition based on a gemara in Eiruvin that applies the prohibition to tying various parts of a tefillin strap into a knot. Presumably if kosheir applies to tying two ends of a rope together the essence of the melakha isn’t fastening; nothing is being connected or fused.
Even if kosheir forbids this scenario, it may still be defined as an act of fastening; the strip of leather or rope is still being fastened by tying its two loose ends together! What about crafting a knot on the edge of a string or rope? Would that violate kosheir? In this instance absolutely nothing is being fastened, but a knot is still being fashioned. The Yerei’im (274) prohibits this as kosheir, whereas the Ohr Samei'ach claims that no prohibition is violated unless two separate items are fastened together. This debate may reflect two very different versions of the prohibition of kosheir.
Admittedly this question may also have been debated by the Tanna’im in two different disputes. R. Meir and the Rabbanan (Shabbat 111) debate whether a knot that can be undone with one hand is prohibited. Presumably, the debate surrounds a robust and durable knot (possibly even a professionally manufactured one) that can be released with one hand. If left undisturbed, the knot may last permanently, yet the ability to release it one-handedly renders it permissible according to R. Meir. Perhaps R. Meir claimed that the issur is defined as creating a formal knot, and by definition a knot that can be released so easily is not considered a kesher. Of course, the Rabbanan, who disputed this claim and prohibited even these forms of knots, may have also defined the prohibition as creating a formal knot, but they insisted that the definition of a formal knot is based on durability and possibly professional crafting, and not the ease of releasing it.
Among those who disagreed with R. Meir and prohibited even knots that can be released with one-hand, a secondary debate ensued about the status of a bow. It is not clear what type of bow is under discussion, but it is clearly not a double knot or a professionally designed knot. R. Yehuda claimed that bows are Biblically forbidden, whereas the Rabbanan claimed that they are not. It is possible that the Rabbanan maintained that a bow – although durable and strong – does not reflect the classic features of a knot and is therefore not Biblically forbidden. R. Yehuda, in contrast, may have dispensed with formal concerns, defining the prohibition in purely practical terms – any strong and durable fastening mechanism is forbidden.