When a conflict arises between the perfomance of two mitzvot, the general rule to decide which one to pursue is osek bemitzvah patur min hamitzvah, one who is engaged in one mitzvah is exempt from other mitzvot. Thus, for example, one who is traveling to redeem captives is exempt from the mitzvah of sukka. This rule is extrapolated from the verse that requires one to recite Keriat Shema, “uvelechtecha baderech,” “and as you travel on the road,” which teaches that the obligation exists only when one is traveling for one’s own purposes (lechet didcha), but if one is traveling in pursuit of another mitzvah, one is not obligated to recite Keriat Shema. The Talmud understands that this exemption is not limited to the mitzvah of Keriat Shema; rather, it is a general rule that one who is already engaged in one mitzvah is exempt from performing other mitzvot.
Does the rule of osek bemitzvah patur min hamitzvah apply to the mitzvah of talmud torah such that one engaged in Torah study would be exempt from performing other mitzvot? At first glance, it would seem that talmud torah should certainly be no worse than any other mitzvah. If the rule of osek bemitzvah applies to mitzvot in general, it should certainly apply to the lofty mitzvah of talmud torah, which, according to the Mishnah, is tantamount to all the other mitzvot.
However, the Gemara (Moed Katan 9b) indicates differently:
הדר יתבי וקא מבעי להו: כתיב יקרה היא מפנינים וכל חפציך לא ישוו בה, הא חפצי שמים – ישוו בה, וכתיב וכל חפצים לא ישוו בה – דאפילו חפצי שמים לא ישוו בה! – כאן במצוה שאפשר לעשותה על ידי אחרים, כאן – במצוה שאי אפשר לעשותה על ידי אחרים.
They [the members of the beit midrash] again sat and asked: It is written: “She [the Torah] is more precious than pearls and all of your pursuits do not equal it,” implying that the pursuits of Heaven [i.e. mitzvot] do equal it [and one would be required to cease learning in order to do mitzvot]. But it is also written: “And all pursuits do not equal it [the Torah],” implying that even the pursuits of Heaven [mitzvot] do not equal it [and one should therefore not cease learning Torah in order to do mitzvot]?! [They answered:] Here [the second verse] deals with a mitzvah that can be performed by others [i.e., in such a situation one does not cease learning, but rather allows the mitzvah to be accomplished by others], here [the first verse] deals with a mitzvah which cannot be performed by others [i.e., in such a situation one ceases learning in order to perform the mitzvah].”
The Gemara thus establishes an entirely different rule which governs whether or not to pursue the mitzvah of talmud torah or another mitzvah: If the mitzvah can be taken care of by others (efshar la’asotah al yedei acheirim), one does not interrupt learning Torah, but if the mitzvah cannot be accomplished by others (iy efshar la’asotah al yedei acheirim), one does interrupt learning Torah for that mitzvah. With regard to talmud torah, it appears that the relevant issue is not whether or not one was previously involved in Torah study, but rather whether or not the other mitzvah can be accomplished by others. This leads to the conclusion that despite being engaged in Torah study, one may have to cease learning Torah in order to pursue another mitzvah, as is the case for a mitzvah which cannot be accomplished by others.
Indeed, the Meiri concludes from the Gemara:
אף על פי שאמרו העוסק במצוה פטור מן המצוה אין תלמוד תורה בכלל זה.
“Even though they [the Sages] said, ‘One who is engaged in a mitzvah is exempt from [another] mitzvah,’ talmud torah is not included in this rule.”
The Meiri explains the rationale behind this exception:
ואף על פי שהעוסק במצוה פטור מן המצוה, לא נאמר כן בתלמוד תורה הואיל ועקרה לידיעת קיום שאר מצות מבטלין אותה בשביל כל מצוה שאי אפשר לקיימה על ידי אחרים.
“Even though one who is engaged in a mitzvah is exempt from [another] mitzvah, this [rule] is not stated with regard to talmud torah because the principal [purpose of talmud torah] is for the knowledge of fulfilling the rest of the mitzvot; [therefore] we negate it for any mitzvah which cannot be performed by others.”
Because the primary goal of studying Torah is to know how to perform the other mitzvot, it is logical, claims the Meiri, that the theoretical study of mitzvot should give way to their actual performance and implementation.
The conclusion drawn from the Gemara in Moed Katan is further supported by the Gemara in Shabbat (11a). There, Rabbi Yochanan rules:
כגון אנו מפסיקין לקריאת שמע ולתפלה.
“[People] like us interrupt [Torah study] for both Keriat Shema and prayer.”
The standard Jew is required to interrupt his Torah learning in order to recite Keriat Shema and pray. From here, too, it is evident that one who is engaged in Torah learning is not exempt from other mitzvot that present themselves.
The Difficulty in the Ruling of the Rambam
The conclusion of the Meiri from the Gemarot that the rule of Osek Bemitzvah Patur Min Hamitzvah does not apply to the mitzvah of talmud torah is clearly not shared by the Rambam. With regard to delaying marriage in order to learn Torah, the Rambam (Ishut 15:2) rules:
וכיון שעברו עשרים שנה ולא נשא אשה הרי זה עובר ומבטל מצות עשה, ואם היה עוסק בתורה וטרוד בה והיה מתירא מלישא אשה כדי שלא יטרח במזונות ויבטל מן התורה הרי זה מותר להתאחר, שהעוסק במצוה פטור מן המצוה, וכל שכן בתלמוד תורה.
Once [a man] has passed age twenty and has not married a woman, he has violated a positive commandment [of peru urvu], but if he was involved with Torah and busy with it and he was afraid to marry a woman so that he would not need to be burdened in making a livelihood and become idle from Torah study, it is permissible for him to delay, for one who is involved in a mitzvah is exempt from [another] mitzvah, and all the more so with regard to talmud torah.
The Rambam unequivocally rules that despite the fact that delay of marriage past age twenty constitutes a violation of the mitzvah of peru urvu, if one is engaged in Torah study, he need not marry because the fact that he is engaged in talmud torah exempts him from the mitzvah of peru urvu. The Rambam clearly thinks that the rule of osek bemitzvah is equally, or more, applicable to talmud torah. How can the Rambam maintain such an assertion? Doesn’t this ruling run counter to the Gemara in Moed Katan?
To further complicate matters, the Rambam (Talmud Torah 3:4) also unambiguously codifies the above-quoted Gemara in Moed Katan:
היה לפניו עשיית מצוה ותלמוד תורה אם אפשר למצוה להעשות ע”י אחרים לא יפסיק תלמודו, ואם לאו יעשה המצוה ויחזור לתלמודו.
If one had the performance of a mitzvah and talmud torah before him, if it is possible for the mitzvah to be accomplished by others, he should not stop his learning, and if not, he should perform the mitzvah and return to his learning.
The difficulty in the Rambam is thus twofold. First, the Rambam in Hilchot Ishut employs osek bemitzvah with regard to talmud torah, as opposed to the rule established in Moed Katan distinguishing between mitzvot that can performed by others and those that cannot. Second, the Rambam in Hilchot Talmud Torah does indeed rule that one must cease learning Torah in order to perform a mitzvah that cannot be taken care of by others, thus creating an internal contradiction within the Rambam between Hilchot Ishut and Hilchot Talmud Torah.
Approaches of the Acharonim in Explanation of the Rambam
Various suggestions are offered by the Acharonim to reconcile the apparent contradiction within the Rambam. The Aruch HaShulchan writes that the Rambam agrees that fundamentally one who is engaged in talmud torah is not exempt from other mitzvot. However, there is room to distinguish between a mitzvah overet, a mitzvah whose window of opportunity to perform is closing, and a mitzvah she’einah overet, a mitzvah whose time is not passing. When a man is twenty years old, the mitzvah of peru urvu, which is accomplished by producing one son and one daughter, can be classified as a mitzvah she’einah overet because there is time to fulfill the mitzvah later. Specifically with regard to the mitzvah she’einah overet of peru urvu, then, the Rambam rules that one may allow talmud torah to take precedence, because the mitzvah of peru urvu is really just being delayed, and not forgone. Thus, the ruling of the Rambam in Hilchot Talmud Torah (that talmud torah is not governed by the principle of osek bemitzvah) is the rule, and his ruling in Hilchot Ishut (that one may delay marriage if one is learning Torah) is the exception for cases when talmud torah is conflicting merely with a mitzvah she’einah overet.
The Maharam Schick offers a different resolution. In reality, the only operating principle in deciding whether or not to stop learning Torah in order to perform a mitzvah is evaluating whether or not the mitzvah is able to be performed by others. The mitzvah of peru urvu, claims the Maharam Schick, is actually a mitzvah which can be performed by others. Because the purpose of the mitzvah of peru urvu is to populate the world, it is by its nature an obligation which devolves upon the community as a whole. Each individual, however, can claim that the world will be populated irrespective of his personal participation. Thus, the mitzvah is defined as efshar la’asotah al yedei acheirim. If this premise is accepted, the contradiction in the Rambam is easily resolved. In Hilchot Ishut, the Rambam rules that one may delay marriage in order to continue learning Torah because the mitzvah of peru urvu can be attended to by the rest of the world. This is consistent with Hilchot Talmud Torah, where the Rambam rules in accordance with the Gemara in Moed Katan that one must cease learning Torah in order to perform a mitzvah that is iy efshar la’asotah al yedei acheirim.
The Shulchan Aruch HaRav posits a third solution based on a novel idea he advances about the mitzvah of talmud torah. According to the Shulchan Aruch HaRav, the mitzvah of talmud torah consists of two, distinct components: Esek hatorah and yediat hatorah. Esek hatorah is the daily and nightly obligation to be constantly (to the degree possible) engaged in learning Torah; yediat hatorah is the obligation to attain mastery over the entire corpus of Torah. He posits that the Rambam understood that when the Gemara in Moed Katan establishes that a mitzvah which is iy efshar la’asotah al yedei acheirim takes precedence over talmud torah, it only refers to the esek hatorah aspect of talmud torah. Because the mitzvah of esek hatorah is both constant and never completed, it is logical that one should interrupt it in order to do other mitzvot, since one will never “finish” the mitzvah of esek hatorah in any event. However, if interrupting one’s Torah learning will interfere with achieving yediat hatorah in an irreparable way, then there is no obligation to cease learning. Thus, the Rambam’s ruling in Hilchot Talmud Torah that one should stop learning Torah in favor of a mitzvah which cannot be accomplished by others is with regard to the mitzvah of esek hatorah. His ruling in Hilchot Ishut that one may delay the mitzvah of peru urvu in deference to the mitzvah of talmud torah is with regard to the mitzvah of yediat hatorah, as taking on the responsibility of supporting a family may prevent a person from achieving mastery over the whole Torah.
The Approach of Rav Aharon Lichtenstein
These three creative suggestions of the Acharonim in explanation of the Rambam, while differing in specifics, share a certain general approach. They all agree that what the Rambam writes in Hilchot talmud torah is the rule and what he writes in Hilchot Ishut is an exception. The rule is that Torah learning is interrupted for a mitzvah that cannot be performed by others (i.e., there is no exemption of osek bemitzvah with regard to talmud torah); the exception is that talmud torah can override peru urvu, either because peru urvu is merely being postponed and not canceled (Aruch HaShulchan), it can be performed by others (Maharam Schick), or because the mitzvah of yediat hatorah will be compromised (Shulchan Aruch HaRav). The weakness of this general approach is that it does not remain loyal to the language of the Rambam in Hilchot Ishut:
שהעוסק במצוה פטור מן המצוה וכל שכן בתלמוד תורה.
“For one who is involved in a mitzvah is exempt from [another] mitzvah, and all the more so with regard to talmud torah.”
The clear implication of these words is that the same fundamental exemption of osek bemitzvah that is relevant to all other mitzvot also applies to talmud torah.
Rav Aharon Lichtenstein advances a final explanation that conforms more strictly to the language of the Rambam in Hilchot Ishut and sheds light on the nature of authentic talmud torah. Our initial assumption that the rule of osek bemitzvah does not apply to talmud torah is, in fact, invalid. As the Rambam expresses it in Hilchot Ishut, if one who is engaged in an ordinary mitzvah is exempt from other mitzvot, certainly one who is engaged in the exalted mitzvah of talmud torah should be exempt from other mitzvot. Thus, the principle of osek bemitzvah applies in full force with regard to talmud torah. Why, then, is one required to cease learning Torah in order to perform a mitzvah for which one is personally responsible, as per the Gemara in Moed Katan and Rambam in Hilchot Talmud Torah? If osek bemitzvah really applies to the mitzvah of talmud torah, shouldn’t one be exempt even from mitzvot which cannot be accomplished by others?
Rav Lichtenstein explains that only when one learns with the intention of implementing one’s learning into practical action is authentic talmud torah achieved. Learning “Torah theory,” as it were, with no plan to apply one’s learning in the physical world through mitzvah observance is not an expression of talmud torah. The mechanics of learning Torah on condition of real-world application, “al menat la’asot,” and learning Torah on a purely academic level without plans for real-world application, “shelo al menat la’asot,” may appear identical, but the former is authentic talmud torah while the latter is just a closely-resembling academic exercise. With this important qualification about authentic talmud torah in mind, it becomes evident why one must stop learning Torah to perform a mitzvah that cannot be performed by others. If one were to continue learning Torah while such a mitzvah fell by the wayside, it would reveal that the Torah being learned is not “al menat la’asot.” Put differently, when a mitzvah which is iy efshar la’asotah al yedei acheirim presents itself to a person who is learning Torah, it is a litmus test for the nature of his Torah learning: if he passes up the mitzvah, he shows that his Torah learning is “shelo al menat la’asot” and invalidates it as true talmud torah; if he pursues the mitzvah, he demonstrates that his Torah study is “al menat la’asot” and justifies it as true talmud torah.
Thus, according to Rav Lichtenstein, the Rambam holds that whenever one’s Torah learning is “al menat la’asot,” the principle of osek bemitzvah applies. In Hilchot Ishut, the Rambam permits a man to continue learning and delay the fulfillment of peru urvu (a mitzvah which cannot be performed by others) because in this case his failure to perform a mitzvah does not prove that his Torah study is “shelo al menat la’asot.” Since he is only delaying the mitzvah of peru urvu until a later date and not completely forgoing it, his talmud torah can be defined as “al menat la’asot” and the principle of osek bemitzvah may therefore be invoked.
 Sukka 25a, Rashi “shluchei mitzvah”
 Sukka 25a. See Berachot 11a and Tosafot, Sukka 25a “uvelechtecha.”
 Pe’ah 1:1
 This category would include both mitzvot that cannot be performed by others for practical reasons (such as no one else is present or cognizant of the need) and mitzvot that fundamentally can never be performed by others because they are personal obligations (such as the obligation to recite Keriat Shema or put on tefillin). Meiri, Moed Katan 9b.
 Meiri, Moed Katan 9b
 I.e., the vast majority of people, as opposed to people like Rabbi Shimon bar Yochai and his contemporaries, who can be described as “toratan umnatan,” “their Torah is their trade.” These people learn Torah so incessantly that they are only required to cease in order to perform Biblical mitzvot like Keriat Shema, but may ignore Rabbinic mitzvot like Tefilla while they are learning. This is the position of the Talmud Bavli. According to the Yerushalmi (Shabbat 1:2), these people need not stop learning Torah even for Keriat Shema (although they must stop for other Biblical mitzvot).
 The commandment to have children. See Bereishit 1:28 and 9:1,7.
 See also Rambam (Megilla VeChanuka 1:1) where he rules: וכן מבטלים תלמוד תורה לשמוע מקרא מגילה קל וחומר לשאר מצות של תורה שכולן נדחין מפני מקרא מגילה. The fact that the Rambam employs this kal vechomer implies that the rule of osek bemitzvah applies to talmud torah. Otherwise, one would counter the Rambam’s ruling by claiming that only talmud torah is canceled by Megilla, but other mitzvot are not canceled by Megilla because one who is engaged in them can claim the exemption of osek bemitzvah.
 Even Ha’ezer 1:13
 Responsa Maharam Schick, Even Ha’ezer 1
 According to Maharam Schick, this was indeed the claim of Ben Azzai, who never married due to his preoccupation with Torah learning. See Yevamot 63b.
 To accept the assertion that the mitzvah of peru urvu is efshar la’asotah al yedei acheirim is in fact quite difficult. The simple understanding of the Mishnah (Yevamot 61b) is that peru urvu is incumbent upon each Jewish male. To suggest that based on the presumed rationale behind the mitzvah of peru urvu we may exempt individuals from fulfilling it when the world will be populated in any event is quite extreme and may possibly be classified as “doresh ta’ama dekra,” interpreting the reason behind a mitzvah in a manner that affects the halacha, which in general is not done. See, for example, Kuntres Acharon 1 to Shulchan Aruch HaRav, Hilchot talmud torah 3:1.
 Shulchan Aruch HaRav, Hilchot talmud torah 3:1. See also Kuntres Acharon 1 there.
 Although the Torah is infinitely deep and can therefore never be fully mastered by man, the Shulchan Aruch HaRav writes that there is a finite definition of the entire corpus of Torah for the purposes of the mitzvah of yediat hatorah. See Shulchan Aruch HaRav, Hilchot talmud torah 1:4-5.
 Thus, even the Shulchan Aruch HaRav’s explanation that the mitzvah of yediat hatorah exempts one from other mitzvot fails to align completely with the wording of the Rambam, which implies that the same exemption of osek bemitzvah which applies to all mitzvot should certainly apply to the mitzvah of talmud torah, not that only a particular component of talmud torah outweighs other mitzvot.
 Be’inyan HaOsek BaTorah Patur Min Hamitzvah, originally printed in Sefer Kevod HaRav, pages 187-201, and reprinted in Minchat Aviv.
 The practical result of Rav Lichtenstein’s analysis is very similar to that of the Aruch Hashulchan: Both agree that one need not cease learning Torah if one is merely delaying another mitzvah and not disregarding it entirely. However, the conceptual underpinnings behind this result differ greatly.
 Although the Rambam writes that one who does not marry by age twenty is “mevatel mitzvat aseh,” Rav Lichtenstein presumably understands that he is “mevatel” the mitzvah for the time being, but if at a later point he marries and has children, then he does fulfill the mitzvah of peru urvu (see Rambam, Hilchot Mila 1:2, for a similar construct with regard to the mitzvah of mila.) Thus, one who is learning Torah is permitted to delay marriage (usually a “bitul aseh”) based on osek bemitzvah because he will fulfill the mitzvah later.