Erasing letters or removing ink to create an empty space large enough to write at least two letters in its place constitutes the av melachah of mochek.1 Essentially, mochek is the opposite of kotev (writing), and the same parameters apply. As such, on a Biblical level, one is only forbidden to erase ink that is not easily rubbed out, from a surface where ink can stick and not be smudged.

Mochek in the Mishkan

The walls of the Mishkan were made from boards of acacia wood. To know exactly how they should be attached to one another, letters were marked on each board. If the wrong letter was written, it was erased, and the correct letter was written in its place.2 The erasing of these letters is the source for the melachah of mochek3.

‘Constructive’ Erasing

In the Mishkan, mochek was done when a letter was written incorrectly and needed to be erased so that it could be rewritten; therefore, the Biblical prohibition refers to erasing or removing something with the intention of writing or drawing something else in its place.4

Some authorities5 argue that if the erasing itself is constructive (e.g., erasing an item from a cluttered list, making it neater), it is included in the Biblical prohibition, even though it was not done with the intention to rewrite.

Removing wax or stains that obscure a word in a book is also considered mochek; since the words are now able to be read, it is considered as if they have been erased and rewritten.6

Rabbinic Additions

The Sages extended the melachah to include erasing something that is easily rubbed out, even if it is on a surface where it would not have remained.7 They also forbade erasing even when one has no intention to rewrite something in its place.

Therefore, one may not tear open a wrapper on Shabbat if there are words on the wrapper that will be broken by the tear.8

Cakes, Cookies, and Chocolate

The Rama9 writes that one may not slice a cake that has words on it made from chocolate or icing etc., because slicing the letters is an issue of mochek. Rabbi Yechezkel Landau10 disagrees, and maintains that mochek is not an issue here. The Mishnah Berurah11 concludes that while one may not slice such a cake, one may rely on the lenient ruling of Rabbi Landau when it comes to eating something that has words on it. The Alter Rebbe12 does not seem to agree with this leniency, and he only allows it only for children.

For this reason, it is advisable that one should avoid buying cakes for Shabbat that have shapes or letters on them. If one did buy such a cake, he or she can avoid the issue by cutting off the top layer of the icing or by removing the letters before cutting the cake.13 Cutting the cake before Shabbat and leaving it in its original setup is also an option, and there is no issue of mochek when people take a piece and break up the words which were formed by the separate pieces of cake positioned alongside one another.14

When letters are embossed on a food, like a cookie or chocolate, many authorities15 maintain that there is no issue of mochek at all and one may break the food even if he is not eating it. The Alter Rebbe’s16 opinion, however, is that such foods may only be eaten but not broken beforehand. Gingerbread men and other foods shaped in a particular form may be eaten17 as long as they are not in the shape of a letter.18

Books and Puzzles

The halachic authorities19 debate whether one may open a book on Shabbat which has letters written on the edges of the pages, since the words are broken when the book is opened. The Alter Rebbe20 presents both opinions and concludes that the custom is to be lenient.21 The same ruling would apply to breaking up a puzzle on Shabbat.22

Common Activities to Avoid:

  • Wiping a whiteboard clean.
  • Ripping open a wrapper where there are words printed on it.
  • Whiting out words written incorrectly.