Five Things Which Cause One to Forget What He Has Learned
The Gemara (Horayot 13b) states: “Our Sages taught: Five things cause one to forget the Torah one has learned: One who eats food which a cat or mouse have eaten from, one who eats the heart of an animal, one who eats olives regularly, one who drinks water which has been used for washing, and one who washes one’s feet one on top of the other. Some say also one who places a vessel under one’s head.”
Regarding eating an animal’s heart, although it is indeed advisable to abstain from eating heart as it causes one to forget, there is no actual prohibition to do so.
Regarding eating olives, when analyzing the Baraita carefully, the Baraita states “One who eats olives regularly” and not just “One who eats olives.” Maran Rabbeinu Ovadia Yosef zt”l writes that that the word “regularly” is indeed specific, for if one eats them only sparingly and not regularly, this will not cause one any forgetfulness. Hagaon Harav Shlomo Zalman Auerbach zt”l would say so as well. Nevertheless, it is quoted in his name that if one eats olives once a month, this is already considered one who eats olives “regularly.”
Hagaon Harav Yosef Chaim Zonenfeld zt”l writes in his Responsa Salmat Chaim that if one eats olives along with olive oil, this will prevent one from becoming forgetful, for olive oil is beneficial for one’s memory. Indeed, the Gemara states that in this instance, the son’s power is greater than the father’s. for the olive, which is the “father”, causes forgetfulness while olive oil, the byproduct of the olive, is beneficial for one’s memory. Thus, if one dips the olives in olive oil, one need not be concerned at all. Many G-d-fearing individuals customarily act accordingly.
Forgetting Words of Torah
The Torah states, “Guard yourself and your soul very much lest you forget”; the Mishnah in Pirkei Avot (Chapter 3, Mishnah 10) explains that this verse warns about forgetting Torah. The Poskim discuss whether or not eating things which cause forgetfulness are included in the prohibition to forget the Torah. Indeed, the Meiri writes that this does constitute the prohibition of forgetting the Torah and therefore, if an individual is obligated to wash his hands, such as if one wakes up from his sleep or if one leaves the restroom, and does not do so, besides for transgressing the edict of our Sages who instituted that one must wash his hands, one transgresses an additional prohibition of causing himself to forget words of Torah, for not washing one’s hands when one is required to causes one to forget and, as we have explained, there is a Torah prohibition to forget words of Torah.
Similarly, Hagaon Harav Eliezer Papo zt”l (author of the Sefer Peleh Yo’etz) writes that if one is not careful regarding all of the things mentioned by our Sages which cause forgetfulness, one must be concerned lest he be included in the teaching of our Sages (in Masechet Avot) which states, “One who causes himself to forget any Torah one has studied is taking his life into his own hands, as the verse states, ‘However, guard yourself and your soul very much lest you forget.’” Hagaon Chazon Ish rules likewise. On the other hand, other great Acharonim are doubtful about this matter, for it is not absolutely certain that doing these things will cause one to forget one’s Torah; rather, one who does these things is merely prone to forgetfulness similar to other Segulot (auspicious matters). Furthermore, it is possible that one will do other things that are beneficial for one’s memory and the end result will be that one will not forget anything at all. Thus, others write that there is no prohibition whatsoever to eat the above items. In cases like these, we have a great rule that whenever there is a disagreement among the Acharonim, if we find any one of the Rishonim who discusses this issue, his words will act as the deciding factor, for the Rishonim were greater than the Acharonim.
Indeed, Rabbeinu Yehuda Ha’Chassid (one of the great Rishonim) writes as follows in his Sefer Chassidim: “An individual once asked a scholar if he was permitted to eat a loaf of bread which a mouse had eaten from (about which the Gemara in Masechet Horayot states that eating from such bread causes one to forget). The scholar asked, ‘Why would you not eat it?’ The man replied, ‘I am afraid that I will forget my Torah learning and I am usually careful not to eat things which cause one to forget but I am hungry now.’ The scholar answered, ‘You need not abstain from eating this bread since the Mishnah in Avot states that one is not liable for forgetting the Torah until one actually sits and purposely makes himself forget (however, in this instance, one would not be liable, for one is not certainly and advertently causing himself to forget). Nevertheless, I see that you are empty and waste your valuable time on anything but Torah study so it would be better for you not be as careful from eating foods that cause forgetfulness so that you indeed forget all of the futile things you are involved with.’” Based on this, Maran Rabbeinu Ovadia Yosef zt”l rules on the aforementioned disagreement between the Acharonim and writes that it is certainly preferable to abstain from eating such foods; however, there is no actual prohibition to do so.