The obligation to guard one’s memory:^[1]

It is a biblical prohibition for one to forget his Torah learning.^[2] Numerous hazards recorded in the Talmud and Poskim are due to that lack of keeping them can damage one’s memory of his Torah learning. This is known as “Kasha Leshichicha.” Nonetheless it is not clear if a person is obligated be careful to adhere by these hazards, and if doing so is optional, or a Rabbinical or even biblical obligation and if one who does not abide by them transgresses the above negative command against forgetting one’s Torah learning. Some Poskim^[3] indeed rule that there is no actual obligation to abide by the memory loss hazards, as would only transgresses forgetting his Torah learning if he does something active to remove it from his heart. However, from other sources it is evident that one is obligated to abide by these matters^[4], and some Poskim^[5] even hold that one who transgresses it, transgresses a Biblical prohibition against forgetting one’s Torah learning.

Who should avoid matters that cause memory loss?^[6] It is questionable whether memory loss hazards are applicable to ignoramuses, women, and children, who do not have the same level of obligation in Torah learning. The following is a Halachic analysis on the subject: Torah scholars are to beware very much from those matters that cause forgetfulness.^[7] Some Poskim^[8] rule that non-Torah Scholars, and certainly women, however, do not need to be careful in this matter, and on the contrary, it is better that they not abide by it so they can forget all the nonsense that they enter their minds. Other Poskim^[9], however, imply that these warnings apply to all men but not to women. Other Poskim^[10] rule that it applies also to pregnant women, although all other women may eat it. Others write it applies also to nursing women and to women at the time that they can become pregnant.^[11] Other Poskim^[12] rule that it applies to all people, man or woman. Regarding children, some Poskim^[13] write that even children are to be careful to avoid matters that cause memory loss, while other Poskim^[14] write that there is no need for them to be careful in this as they have not learned anything that they can forget.

Safek-Being lenient in a case of doubt: Some Poskim^[15] rule that even in a case of doubt, one may not be regarding those matters that cause memory loss and they are similar to other matters of danger. Other Poskim^[16] however rule that one may be lenient in the case of doubt.

Overview-The prohibition to forget one’s Torah learning:^[17]

It states in the Mishnah in Avos^[18], “Whoever forgets even a single teaching from his study, is considered by Scripture to be liable for his life, as the verse^[19] states, “Make sure to guard yourselves and guard your souls very much, lest you forget the words that your eyes saw.” The Talmud^[20] teaches us based on this verse, that whoever forgets even one matter from his studies transgresses a negative command. There are the various opinions in Rishonim regarding the severity of one’s forgetting of his Torah learning.

1. The opinion of the Rambam: The Rambam^[21], as well as many others who enumerate the list of the 613 commands, omit the above prohibition of forgetting one’s Torah learning from the list of 365 negative commands. This seems to imply that it is not a prohibition at all, and at least not a biblical prohibition.
2. The opinion of the Ramban: The Ramban^[22], unlike the Rambam, does enumerate the verse of “thou shall not forget..” as part of the 613 commands. However, as he understands it, this prohibition is not referring at all to forgetting one’s Torah learning but rather to forgetting the giving of the Torah on Mount Sinai. Thus, he too does not list the forgetting of one’s Torah learning as a biblical prohibition. According to the Ramban, it seems that he understands the statement in the above Mishneh in Avos and Talmud which seems to prohibit forgetting one’s Torah learning, to simply be a matter of piety which is supported by the above verse in Scripture, although it is not an actual obligation.
3. The prohibition is only when one stops learning Torah altogether: Indeed, there are a number of Rishonim who enumerate the above prohibition of forgetting one’s Torah learning as part of the 613 commands, hence accepting the above Mishnaic and Talmudic teaching as literal.^[23] Nonetheless, even they describe the prohibition is only applicable to one who completely drops his Torah learning, and get themselves involved in trivial matters which causes his Torah learning to become forgotten.
4. The opinion of the Alter Rebbe:^[24] The Alter Rebbe has a very unique and detailed approach in his understanding of the above Mishnaic and Talmudic prohibition of forgetting one’s Torah learning. In his laws of Torah study, the Alter Rebbe states based on Rabbeinu Yonah^[25],  that whoever forgets one aspect of his Torah learning due to him not reviewing it properly is considered by Scripture to be liable for his soul, and likewise transgresses a negative command in the Torah. Meaning, that not only does he hold that forgetting one’s Torah learning is under a biblical prohibition, but that it is transgressed even if one does not actively do anything to make him forget it, but simply is not active enough to retain the information that he acquired, such as if he does not review his learning. Even in today’s times that all the laws have been written in books, and anything that one has forgotten can be researched, nonetheless, the moment that one forgets his learning he transgresses the above negative command prior to looking it up. In his Kuntrus Achron^[26], the Alter Rebbe explains this to be likewise the opinion of the Rambam who more than once mentions of the idea of not forgetting one’s Torah learning.
5. The opinion of the Rebbe:^[27] Even according to the approach of the Alter Rebbe in his understanding of the prohibition against forgetting Torah, the prohibition is specifically in a case that one actively does something to neglect Torah learning in general. If, however, he does not actively neglect Torah learning and simply avoids reviewing certain sections of Torah due to lack of time, then since he has not neglected Torah learning therefore no prohibition is considered to have taken place.

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[1] See Sefer Shemiras Haguf Vihanefesh [Lerner] Mavo 17-19; Hakashrus page 433.

[2] Admur Hilchos Talmud Torah 2:4; Avos 3:8; Menachos 99b

[3] Mishneh Halachos 3:62 and 5:101; Sefer Zikaron 2 Hakdama, based on Sefer Chassidim 1008; Yabia Omer 2 Y.D. 8; Taharas Hamayim Shin 14

[4] Setimas Kol Haposkim who record memory loss hazards; Reishis Chochmah Shaar Hakedusha 5; All Poskim in  next footnote.

[5] Hisorerus Teshuvah 1 and 367; Chesed Lealafim 157:6; Shem Mishimon Y.D. 17; Divrei Malkiel 4:1; Mili Deavos 5 Y.D. 5-3; Salmas Chaim 1:41; Likkutei Maharich; Teshuvos Vehanhagos 3 in name of Chazon Ish; Lehors Nasan 1:59

[6] See Sefer Shemiras Haguf Vihanefesh [Lerner] Hakdama 19

^[7] Magen Avraham 170:19 writes that although by olives those which have correct intentions do not need to beware from eating them, nevertheless regarding the heart he writes that all are to be stringent.

[8] See Sefer Chassidim 1008; P”M 72 A”A 7, brought in Darkei Teshuvah 72:5; See Chochmas Adam ibid that only the Midakdekin are careful in this; Tel Talpiyos 5:140-3; Vayitzbor Yosef 43; Yad Yitzchak 2:84-17; Givas Pinchas 65:11-44; Darkei Teshuvah 72:5; Kaf Hachaim O.C. 157:18; Y.D. 72:6; Sefer Zikaron 2 Hakdama; Yabia Omer 2 Y.D. 8

[9] Chavas Daas Y.D. 72:2; Darkei Teshuvah 72:5; Givas Pinchas 65:11-44; Sefer Zikaron Hakdama 2

[10] Beis Lechem Yehuda 72:3; Kneses Hagedola; Mishmeres Shalom 72 S.D. 2; Ben Ish Chaiy Acharei 2:11

[11] Sefer Zechira Inyanei Zivug; Ben Ish Chaiy Acharei 2:11 regarding nursing

[12] Halichos Beisa 28 footnote 24; Kaf Hachaim [Falagi] 24:45 that a woman once ate an animal heart and got severely injured; Kaf Hachaim 157:18; Givas Pinchas 65:11-44 in answer of his brother in law in end of Sefer in name of Ruach Chaim and that so is implied in Mishnas Chassidim; Implication of Kaf Hachaim ibid who writes that the worry is not just to due memory loss, but also due to the Yetzer Hara; See Shulchan Chaiy 9 footnote 2

[13] Sefer Zikaron; See Hakashrus page 423.

[14] Eineiy Kol Chaiy Horiyos 13; Vayitzbor Yosef 42

[15] Shem Mishimon Y.D. 17

[16] Mili Dechassidusa 50

[17] See Likkutei Sichos Vol. 34 Parshas Vaeschanon; Divrei Avos 3:8 and Divrei David Avos 3 of Ashel Avraham of Butchach; Sefer Shemiras Haguf Vihanefesh [Lerner] Mavo 17

[18] Avos 3:8

[19] Vaeschanon 4:9

[20] Menachos 99b

[21] See also Rambam Talmud Torah 1:10, 12, brought in Kuntrus Achron Talmud Torah 3

[22] In Hashmatos of Sefer Hamitzvos L.S. 2

[23] See Semag Lavin 13; Semak 15; Yireim 28

[24] Admur Hilchos Talmud Torah 2:4

[25] See Rabbeinu Yonah Avos ibid.

[26] Beginning of chapter 3

[27] Likkutei Sichos Vol. 34 Parshas Vaeschanon