The melachah of koshair is the act of binding by tying a knot. Although most knots are prohibited under this melachah, either Biblically or rabbinically, some are permitted.

Koshair in the Mishkan

A unique blue dye was used for the coverings (yeriot) of the Mishkan. This dye was made from a sea creature called the chilazon. To trap the chilazon, fishermen fashioned nets from ropes which were knotted together.1

Halachic literature describes two types of knots with regard to the melachah of koshair:

a) “Kesher uman,” a craftsman’s knot. Although the Mishnah2 gives some examples of a kesher uman, it is difficult to determine precisely which knots are included. In practice, any knot that is very tight and would not come out on its own is considered a kesher uman. This obviously includes sophisticated knots like a fisherman’s bend knot and also less complicated ones like the simple double knot that is commonly made to tie one’s shoes.3

b) “Kesher shel kayama,” a lasting knot, meaning that at the time the knot is made, the one who ties it has no intention of untying it at any specific time. According to Rabbinic Law, as long as the knot is intended to remain for longer than a 24 hour period, it is considered a kesher shel kayama.4

According to Maimonides,5 one only transgresses the Biblical prohibition of koshair by tying a knot that is both a kesher shel kayama and a kesher uman. If it is only one and not the other, prohibition is Rabbinic. If it is neither a kesher shel kayama nor a kesher uman, it is permitted.

Rashi,6 however, maintains that the Biblical prohibition of koshair refers to tying a kesher shel kayama, regardless of whether the knot is a kesher uman. As such, tying any knot with the intention to untie it on the same day is allowed.

Halacha follows Rashi’s interpretation.7 Nevertheless, we are careful to accept the stringencies of both opinions. As such, it is forbidden to make any knot that is intended to stay tied for more than 24 hours, as per Rashi. At the same time, making a kesher uman is prohibited even if one intends to untie it on the same day.8

Common Activities to Avoid

  • Tying the ends of a garbage bag together with a double knot.9
  • Tying one’s shoes with a double knot.
  • Tying a plastic bag around it itself into a knot.10

Most of the time, these issues can be avoided by tying in a permissible way, such as making a slip knot (which is not a real knot) or a bow. A bow is typically made by first winding the two strings around each other and then forming a bow. The initial winding of the string is a type of knot, but is totally permissible since it will easily come undone on its own. The bow on top of it (which is not a knot on its own because it comes apart easily by just pulling one of the strings) is what holds it in place firmly.11 Therefore, a bow is not tight enough to be considered a kesher uman but it can be a kesher shel kayama if one does not intend to undo it on the same day. Making a bow with the intention to untie it on the same day, as is often the case when people make a bow, is permitted.