Contributed by: R. Ezra Mizrahi
The labor of tying a knot, "Qosher", is one of the 39 melachot that are forbidden from the Torah for a Jew to perform on Shabbat. To fully understand this labor, we must first define a couple of terms:
1) Knot - In Hebrew: Qesher. If one takes two strings, overlaps them, and then pulls one through the other, one has created a Qesher by halacha terms. However, this knot is completely permitted on Shabbat, as this knot barely holds together. To clarify, the best example is how one begins to tie one's shoelaces. The first step in tying one's shoelaces is to take each string in one hand and interloop them, and pull. This initial overlapping of strings is considered a Qesher. Of course, in reality this is hardly a knot, and if it would not be for the second step of tying a shoelace (creating the bow) the Qesher would come loose and fall apart. Here is a picture of what is being described:
Creating this Qesher on Shabbat is fully permitted, because as mentioned, one who ties such a Qesher is essentially doing nothing, for the knot will come loose by itself. However, what is forbidden in halacha is when one makes a Qesher on top of a Qesher, which means that one makes two of the above-mentioned knots, one on top of the other. Now this is a real knot, and this is what the halacha is addressing under this prohibition. In similar fashion, another type of real knot that would be forbidden is if one took one string, and looped it over itself and pulled. As experience dictates, this too is a real knot, and aptly, this is the type of knot we are referring to.
2) Slip-Knot - In Hebrew: Anivah. A slip-knot is a knot that can come apart if one pulls one side. The classic example of an Anivah is a modern day men's dress tie, that if one pulls out one side, the entire knot disassembles. A slip-knot is completely permitted by Maran, as it is not even considered under the umbrella of Qosher at all (Maran O.H. 317:5), therefore creating any sort of slip-knot on Shabbat is permitted. However, the halacha for creating a slip-knot together with a regular knot (one-tie) will be discussed in the continuation.
3) Professional Knot - In Hebrew: Qesher Ouman. Described in the gemara as a sailor's knot or the knot that is permanently installed in the nose of a camel, that is only done by a professional. According to the Reif, the mark of this type of knot is that is is very strong and does not come loose early.