Untying a knot, the av melachah of matir, is forbidden on Shabbat. Matir is essentially the exact opposite of koshair, tying. As Maimonides puts it: “Any knot which one would be Biblically liable for tying on Shabbat, one is Biblically liable for untying. Any knot which is rabbinically forbidden to tie, is similarly forbidden by the sages to untie. Any knot that is permitted to be tied on Shabbat may also be untied.”1 Nonetheless, as will be explained below, the laws of matir are sometimes more lenient than those of koshair.

Matir 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.2 At times, a rope needed to be replaced or repaired, which involved untying the knots. The melachah of matir refers to this untying.

In the case of net repair, the matir meant untying a knot in order to tie a stronger one in its place. Tosafot explains that the prohibition therefore only applies to untying a knot in order to tie a stronger one afterwards.3 Simply untying a knot and leaving it untied is not forbidden. Maimonides, however, does not include any such a condition, implying that, in his view, any untying is forbidden, even if nothing will replace the untied knot. Halacha follows Maimonides’ view.4

The laws involving which knots may and may not be tied on Shabbat are discussed in the article on koshair. We will review the basic points here, to determine how they relate to the melachah of matir.

Tying a knot which one does not intend to untie at any specific time is a Biblical prohibition.5 Untying such a knot is likewise considered a Biblical prohibition. For example, one may not untie the knots on tzitzit, which were not intended to ever be undone.

Tying a very tight knot, even if it is only intended to last for a short amount of time (less than 24 hours), is prohibited rabbinically. Similarly, tying a knot which is not so tight, with the intention that it will not be untied for at least another 24 hours, is also rabbinically prohibited.6 As such, untying these knots is also considered a rabbinic prohibition. Rabbi Moshe Isserles rules, however, that these prohibitions are lifted in a scenario where the knot is causing one distress.7 For example, if one cannot put on his shoes because the shoelaces are tied with a double knot, the knot may be undone, since it was not intended to remain for a long time.

A knot which is not very tight and also not meant to last for more than 24 hours is permitted to be tied. Untying it is thus also allowed. For example, shoelaces may be tied with a bow and then be untied on Shabbat.8

In a situation where a bag is tied with a knot which may be undone, but it would be easier to simply rip or cut it open, one may do so.