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Mochek - Erasing On Shabbat

The Daily Halacha Moment - The Melachah Of Mochek (Erasing)

״כל השונה הלכות בכל יום - מובטח לו שהוא בן העולם הבא״ (נידה עג ע״א, מגילה כח:)

“Anyone who studies Halachot every day is guaranteed that he is destined for the world-to-come” (Megilla 28b, Niddah 73a)


What is the Melachah Of Mochek?


The melachah of Mochek was done in the Mishkan if the wrong symbol was mistakenly inscribed on one of the planks of the Mishkan it had to be erased in order to rewrite the correct symbol. [1] Thus, the purpose of erasing is the act of erasing or preparing a surface for the purpose of ultimately writing. The melachah of Mochek can also be transgressed when erasing for any purpose even if the surface is not needed for writing or drawing.

As a general rule, the melachah of Mochek applies to any act that reverses or undoes the melachah of Kotev.

One who erases two letters with the intention of writing another two letters in its place transgresses the Av Melachah of Mochek. [2] However, the two letters that one intends to write must be better than the one’s previously. This also applies to one who erases a large letter or a blotch of ink that one has enough space after it is erased to write two smaller letters. [3] It is biblically prohibited to erase even one letter, but one would not be liable to bring a Korban by doing so by accident. [4].

Erasing that accomplishes a purpose, such as erasing a note that one is owed money, or by erasing an extra letter in a sefer Torah, is prohibited because of Mochek, even though one did not erase two letters it may still be considered a Torah prohibition, and not only rabbinical. [5].

Even covering the letters with white-out or other ink is considered Mochek. [6] It is even prohibited to merely put a line through the letters even though one can still read the writing. [7]


[1]. Mesechet Shabbat 103a.

[2]. Shulchan Aruch 340:3. The Bet Yosef explains from the Rosh that even though it was needed in the Mishkan to erase only one letter at times, the Chachamim learn that Mochek is not more stringent than Kotev, and therefore the Av Melachah can only be accomplished through erasing two letters. See also in Biur Halachah, 340, “HaMochek.”

[3]. Shabbat 75b. See also in Chazon Ovadia, Shabbat, vol. 5, p. 206.

[4]. Kaf HaChaim 340:26 in the name of the Shulchan Aruch HaRav.

[5]. Biur Halachah, 340, “HaMochek”; Mishnah Berurah, 340:22 at the end; However, see also in Menuchat Ahavah, vol. 3, p. 152.

[6]. See Chut Shani, Shabbat, vol. 1, p. 156.

[7]. Mishnah Berurah, siman 340, 22:3. Orchot Shabbat 15:48 states that if the letters are still readable, it may not be considered Mochek, but rather it is an issue of Kotev.

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