The Book of Deuteronomy adjures us not to forget, among other things, G-d (e.g., Deuteronomy 6:12 and 8:11), the Sinaitic Revelation (ibid. 4:9), G-d’s covenant with the Patriarchs (ibid. 4:31), the laws of the tithes (ibid. 26:13), and Amalek’s attack (ibid. 25:19). In all these cases, the Torah uses the word “shachach”/“shichachah” to refer to forgetting.
While conjugations of “shachach” appear over 100 times in the Bible, there is also a lesser-known Hebrew word for forgetting: “nash”/“nashah.” When Yosef named his eldest son Menashe, he said, “G-d has made me forget (nashani) all my hardship and all my father’s household” (Genesis 41:51). When Moshe prophesied that the Jewish People would forsake G-d, he said, “You will have forgotten (teshi) the Rock [i.e. G-d] who gave birth to you” (Deuteronomy 32:18).
“Nashah” also means forget in such verses as Lamentations 3:17, Jeremiah 23:39, Isaiah 44:21, Job 39:17, and Job 11:6. An animal’s sciatic nerve, which is forbidden for consumption, is called the gid hanasheh (Genesis 32:33). The Zohar (Bereishis 170b) explains that this nerve is food for the Evil Inclination which causes man to forget his responsibilities to G-d.
The Talmud refers to a married woman’s maiden family as her “bei nasha” (house of nasha). A bevy of commentators explain that when a young woman leaves her parents’ household to get married, she essentially “forgets” her old family and joins her husband’s.
(This explanation was first proposed by the English Tosafists in Tosafos Chachmei Anglia (to Kiddushin 24a) and later by Rabbi Yehuda Chalava [a son of the famous 13th century scholar Maharam Chalava] and his cousin Rabbeinu Bachaya ibn Chalav [in their respective commentaries to Genesis 41:51]. Similar explanations are later proffered by Rabbi Binyamin Mussafia [1606-1675] in Mussaf ha’Aruch and Rabbi Shmuel HaLevi [1625-1681] in Nachalas Shiva.)
Menachem Ibn Saruk writes that the root of “nashani” and “teshi” is the letter shin alone, which represents forgetting. Others (including Ibn Chayyuj, Ibn Janach, and Radak) write that the root may be nun-shin-hey or nun-shin-shin.
Rabbi Shlomo Pappenheim of Breslau (1740-1814) writes in Cheshek Shlomo that the root is nun-shin, which he explains means moving something from its natural condition. This definition is related to forgetting since one forgets something because information in the brain is moved (or removed) from its place.
Rabbi Pappenheim writes that other words derived from this root are “gid hanasheh” (which moves from its place), “nosheh” (a lender, who moves money from his possession to another’s), “nashim” (women, who are said to be less able to remember to stay on task than men), “anush” (a sick, weakly person, whose state of health has been moved from its proper place), and “enosh” (mankind, whose powers are weak in comparison to more powerful spiritual entities).
Elsewhere in Cheshek Shlomo, Rabbi Pappenheim writes that the root of “teshi” is tav-shin, which means weakening. Rabbi Moshe Tedeschi Ashkenazi (1821-1898), the Italian author of Ho’il Moshe, offers the same proposition.
The Malbim (to Job 11:6) writes that the difference between “shachach” and “nashah” is tha “shachach” implies that a person can later remember what he forgot while “nashah” implies that the person forgot the matter so completely that the memory cannot be retrieved.
Rabbi Samson Raphael Hirsch (to Genesis 8:1) writes that “shachach” connotes a person forgetting inadvertently while “nashah” connotes a person forgetting something because he treated the matter flippantly and is therefore partially responsible for forgetting. Elsewhere (Deuteronomy 4:9), Rabbi Hirsch writes that “shachach” implies forgetting as a result of focusing on something else while “nashah” is forgetfulness that results from a weakened memory.
Rabbi Eliyahu Katz (1916-2004), the former chief rabbi of Slovakia and later the chief rabbi of Beer Sheva, disagrees with the Malbim and Rabbi Hirsch. He argues that “shachach” and “nashah” mean the exact same thing, which is why the Targumim tend to translate “shachach” and its cognates into Aramaic as “nashah”-based words. He claims “nashah” is simply an Aramaic way of saying “shachach.”
By way of metathesis, some connect the root shin-kaf-chet to the root kaf-chet-shin (deny or weaken). Rabbi Yekusiel Yehudah Teitelbaum of Sighet (1808-1883) in Yitav Lev (to Exodus 10:1) writes that they are connected because if a person forgets about G-d and his responsibilities towards Him, he will eventually deny His existence altogether. The relationship between these two words is why Psalms 137:5 is usually translated as “If I forget you, O Jerusalem, let my right hand be weakened” even though the key Hebrew word is “tishkach,” which literally means forgotten (see the editors of Daat Mikra on this pasuk).
The Aramaic word shachiach (“common” or “frequent”) shares a common root with “shachach.” Rabbi Moshe Shapiro (1935-2017) notes that this relationship seems counterintuitive: If something is common or frequent, one would expect people not to forget it. Why, then, are the two words related?
Rabbi Shapiro explains that, in fact, common occurrences are mentally filed away as “normal” and therefore are taken for granted and can easily be forgotten. Indeed, the Talmud says, “People will surely remember any bizarre matter” (Chullin 75b). Only the unordinary will surely be remembered. The commonplace is at risk of being forgotten.