The Gemara challenges: And prayer, which is also a matter in which the community is engaged, and we learned in the mishna: One who was standing in prayer and remembered that he is one who experienced a seminal emission and did not yet immerse himself should not interrupt his prayer, rather he should abridge it. The Gemara infers: The reason is because he already began to pray; however, if he did not yet begin, then he should not begin, even by means of contemplation.

The Gemara responds: Prayer is different in that it does not contain the acceptance of the yoke of the kingdom of Heaven. The Gemara rejects this: And Grace after Meals does not contain the acceptance of the yoke of the kingdom of Heaven, and yet we learned in the mishna: Over food, one recites a blessing afterward, but does not recite a blessing beforehand. Rather, the differences must be explained otherwise: The recitation of Shema and Grace after Meals are both mitzvot by Torah law, while prayer is only by rabbinic law. Therefore, one who is impure need not pray.

Rav Yehuda said: From where is the mitzva by Torah law to recite Grace after Meals, derived? As it is stated: “And you shall eat and be satisfied and bless the Lord your God” (Deuteronomy 8:10).

And from where is the mitzva by Torah law to recite the blessing over the Torah before it is read, derived? As it is stated: “When I proclaim the Lord’s name, give glory to our God” (Deuteronomy 32:3), meaning that before one proclaims the Lord’s name by reading the Torah, he must give glory to God.

Rabbi Yoḥanan said: We derived that one must recite the blessing over the Torah after it is read from Grace after Meals by means of an a fortiori inference. And we derive the obligation to recite a blessing before partaking of food from the blessing over the Torah by means of an a fortiori inference. The blessing over the Torah after it is read from Grace after Meals by means of an a fortiori inference: Food, which does not require a blessing beforehand by Torah law, requires a blessing afterward; Torah, which requires a blessing beforehand, is it not right that it requires a blessing afterward? And similarly: The blessing before partaking of food from the blessing over the Torah by means of an a fortiori inference: Torah, which requires no blessing afterward by Torah law, requires a blessing beforehand; food, which requires a blessing afterward, is it not right that it requires a blessing beforehand?

The Gemara notes: The logic of this a fortiori inference can be refuted: What is true with regard to food, where one derives pleasure from eating, is not true with regard to matters which offer no bodily pleasure. Therefore, the blessing over the Torah cannot be derived from the blessing over food. And similarly: What is true with regard to Torah, that provides eternal life to those who engage in its study, is not true with regard to matters that do not provide eternal life. Therefore, the blessing before partaking of food cannot be derived from the blessing over the Torah. Furthermore, we learned in the mishna: Over food, one who is impure due to a seminal emission recites a blessing afterward, but does not recite a blessing beforehand. The mishna does not derive the blessing recited before a meal from the blessing recited over Torah. Consequently, this is a conclusive refutation of Rabbi Yoḥanan’s statement.

Rav Yehuda said: One who is uncertain whether he recited Shema or whether he did not recite it does not recite it again. However, one who is uncertain whether he recited: True and Firm [emet veyatziv], the blessing that follows Shema in the morning, must recite emet veyatziv again. What is the reason for this? In his opinion, the obligation to recite Shema is only by rabbinic law. His ruling follows the principle that in cases of uncertainty involving rabbinic law, the ruling is lenient and he need not repeat it. However, since emet veyatziv is primarily a commemoration of the exodus from Egypt, it is a mitzva by Torah law, and, in cases of uncertainty involving Torah law, the ruling is stringent and he must repeat it.

Rav Yosef raises an objection: How can you say that the obligation to recite Shema is only by rabbinic law when it is explicitly written: “And you shall recite them to your children and speak of them when you sit in your home and when you walk by the way, when you lie down and when you rise” (Deuteronomy 6:7)? Abaye said to him: That verse was written with regard to matters of Torah. One need not interpret the verse in the conventional manner, as obligating the recitation of Shema, but rather as referring to the general obligation to study Torah.

From here, the Gemara attempts to resolve this issue by citing proof from the mishna. We learned in the mishna: One who experienced a seminal emission may contemplate Shema in his heart, but neither recites the blessings preceding Shema, nor the blessings thereafter. Over food which, after partaking, one is obligated by Torah law to recite a blessing, one recites a blessing thereafter, but not beforehand.

And if it would enter your mind that the obligation to recite emet veyatziv is by Torah law, let him recite the blessing after Shema. Since he does not recite the blessing, apparently, he is exempt.

The Gemara refutes this: What is the reason that he recites emet veyatziv? If it is because it deals primarily with the exodus from Egypt, wasn’t it already mentioned in the recitation of Shema, in the portion of the ritual fringes?

The Gemara challenges: And let him say this, emet veyatziv, and he will not need to recite that, Shema. The Gemara responds: While one may commemorate the exodus from Egypt in either Shema or emet veyatziv, Shema is preferable as it contains two elements, both a commemoration of the exodus and an acceptance of the yoke of the kingdom of Heaven.

And Rabbi Elazar said a different opinion: One who is uncertain whether he recited Shema or whether he did not recite Shema, must recite Shema again. According to his opinion, there is a mitzva by Torah law to recite Shema. However, if one is uncertain whether he prayed or whether he did not pray, he does not pray again, as the obligation to pray is by rabbinic law. And Rabbi Yoḥanan said: He must pray again; if only a person would pray throughout the entire day.

And Rav Yehuda said that Shmuel said: One who was standing in prayer and remembered that he already prayed must interrupt his prayer, even in the middle of a blessing. The Gemara challenges this: Is that so? Didn’t Rav Naḥman say: When we were in the school of Rabba bar Avuh we raised a dilemma before him: Those students in the school of Rav who mistakenly recited a blessing from the weekday Amida on Shabbat, what is the ruling with regards to completing the weekday prayer? And Rabba bar Avuh said to us: The ruling is that one must complete that entire blessing. How then did Rav Yehuda say that one must interrupt his prayer even in the middle of a blessing?

The Gemara rejects this: How can you compare the two cases? There, on Shabbat, the individual is one who is obligated and should actually recite all eighteen blessings, and it is the Sages who did not impose upon him in deference to Shabbat and instituted an abridged formula. But here, didn’t he already pray? Therefore he can stop, even in the middle of a blessing.

And Rav Yehuda said that Shmuel said: One who already prayed, and then enters a synagogue to find a congregation standing and praying, if he is able to introduce a new element, an expression or request, into his prayer, he may pray again, and if not, he may not pray again.

The Gemara notes: This concept is identical to Shmuel’s previous statement regarding one who already prayed that he need not pray again. Nevertheless, both statements are necessary. If he had taught us the first halakha, we would have said that applies only to a case involving an individual who prayed and an individual who began to repeat the prayer,