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There are several theories in psychology as to why we forget. One, developed by Edward Thorndike in the early 20th century, is called “decay theory.” In short, any new information creates a neurochemical trace, which will disintegrate over time if the idea is not actively rehearsed.

In the following mishna, Rabbi Dostai, in the name of Rabbi Meir, highlights the challenge of forgetting:

Whoever forgets even a single word of his learning is considered as if he has forfeited his life, as it is stated, “Just be careful, and diligently guard your soul, lest you forget the things that your eyes have seen” (Deuteronomy 4:9). One might think that this applies also to one who [has forgotten because] his studies proved too difficult for him, therefore the verse continues, “that they do not fade from your mind as long as you live.” Thus, one does not forfeit his life unless he deliberately removes them from his heart (Avot 3:10).


Memory is essential for successful Torah learning and Jewish continuity. The consequences for failing to remember are dire. Yet Rabbi Dostai also acknowledges the fact that forgetting is natural, and is sometimes excusable. What are the exact parameters of “his studies proved too difficult for him,” which removes culpability, and he “deliberately removes them from his heart,” which incurs liability? The commentaries provide several approaches, yielding different insights about memory and forgetting.

Most commentators assume that the mishna is not addressing someone who deliberately and actively tries to forget Torah, as that is too obvious a violation to even mention. Rather, deliberately removing Torah from one’s heart includes not reviewing one’s studies out of laziness (Tosfot Yom Tov). However, if one does review sufficiently and still does not remember, that is beyond his or her control.

Another factor that negatively impacts memory is not properly understanding the material when originally learned. When the information is not encoded properly, later retrieval is unlikely. If someone tried to process the information with appropriate learning techniques, but due to lack of full understanding is unable to later remember that information, that would fall under the exemption of “his studies proved too difficult for him” (Rashi).

Others point to a possible motivational barrier to memory that stems from a lack of valuing Torah. As Rabbi Dr. Reuven Bulka writes, “One who forgets obviously has not approached Torah seriously enough, has not seen Torah as so crucial that every word is critical and therefore should be vibrantly remembered.” The assumption is that if we truly cared, we would have a better chance of remembering. To the extent that our forgetting is rooted in lack of proper appreciation of Torah, we would be culpable.

Another factor that impacts our memory of Torah is how busy we are with non-Torah endeavors. In psychology, one of the other theories of forgetting is interference, namely, when other information gets in the way of proper encoding or retrieval of information. To the extent that we don’t have a choice and must get involved with other pursuits like earning a livelihood or performing other mitzvot or responsibilities, presumably this would fall under the category of “his studies proved too difficult for him.” However, as Meiri points out, there are many endeavors we spend our time engaging in that are not necessary, and those do not avail us of an excuse to forget our learning.

It seems clear that in order to avail ourselves of the excuse his studies proved too difficult for him,” we first need to put in proper effort. Rabbi Yosef Hayyun uses the mishna as a springboard to suggest several strategies that would enhance our capacity to remember, and would likely be necessary before justifying forgetting. First, he points to what many other commentaries mention, which is constant and consistent review of material (chazara). He relates a story about a sage who reviewed a new teaching 40 times (Pesachim 72a) and adds the precedent of Rabbi Chiyya who would review his learning every 30 days (Berachot 38b).

These models of reviewing map well onto the current research in memory. In their book Made to Stick: The Science of Successful Learning, Peter Brown, Henry Roediger, and Mark MacDaniel highlight the importance of effortful retrieval of previously learned information. Not only is repeated review important, but also delayed retrieval is essential. This entails recalling information after time has passed, which is an even more potent strategy, because the mental effort of retrieving the information helps strengthen the memories.

Another idea that Rabbi Hayyun suggests that Talmudic precedent and corroboration from recent research is verbally articulating what we are learning out loud (Eiruvin 53b-54a). In 2010, Colin Macleod and colleagues studied the impact of what they deemed the “production effect,” demonstrating that when materials are read aloud, it leads to substantial memory improvement than when read silently. Additionally, Rabbi Hayyun encourages teaching others as an effective way to improve memory. The impact of teaching for a teacher’s own learning success is well documented as the protégé effect (Bargh & Schul, 1980), and one possible mechanism for the improvements in learning is the improved memory that the process of teaching affords (Koh, Lee, and Lim, 2018).

While it is true that forgetting is natural and it is sometimes beyond our control, Rabbi Dostai is reminding us we need to do everything within our control to remember the essential ideas we encounter while learning Torah. We need to overcome laziness, value the content, learn the information clearly, review using proven retrieval practices, and use other techniques that will help us remember, including reciting aloud, teaching to others, and any other strategy that proves effective. By putting in the effort to remember, may we merit the inverse of the cautionary warning of this mishna, and instead be granted a long and prosperous life filled with meaningful messages from the Torah and the sages.


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Rabbi Dr. Mordechai Schiffman is an Assistant Professor at Yeshiva University’s Azrieli Graduate School, an instructor at RIETS, and the Straus Center for Torah and Western Thought. He graduated YU with a BA in psychology, an MS in Jewish Education from Azrieli and Rabbinic Ordination from RIETS, before attending St. John’s University for his doctorate in psychology.He learned for two years at Yeshivat Netiv Aryeh. He has been on the rabbinic staff of Kingsway Jewish Center in Brooklyn, NY since 2010 and practices as a licensed psychologist in NY. His book “Psyched for Torah,” his academic and popular articles, as well as many of his lectures are accessible on his website,