Siman 184

Birkat hamazon must be immediately after the conclusion of the eating, specifically in the place where one ate. And it has already been explained in siman 178 that there are those who say that all of the seven species require a blessing specifically in their place. And there are those who say that only the five species of grain require a blessing in their place; even those whose blessing is not "hamotzi" but "borei minei mezonot" – they require a blessing in their place. But those whose blessing is "ha'etz," even if they are of the seven species – they do not require a blessing in their place, see there. And what is called a "change of place"? From room to room. But in one room, even if it is very large – one may eat in this corner and bless in another corner. And also from room to room, when one sees a portion of it, it is like one place. And if one ate with the intention to bless in another room – it is permitted, as I wrote there.

One who ate and departed, and did not recite the blessing in his place, the Rambam ruled in the fourth chapter that if he acted intentionally—he must return to his place and recite the blessing. And if he acted inadvertently—he recites the blessing in the place where he remembered. And even in a case of intentional action, if he did not return to his place and recited the blessing in the place where he remembered—he has fulfilled his obligation. However, the Tur ruled that even in a case of inadvertent action one is obligated to return to his place and recite the blessing, but if he did not do so and recited the blessing in the place where he remembered—he has fulfilled his obligation. But in a case of intentional action, even if he recited the blessing in the place where he remembered—he has not fulfilled his obligation, and he must return to his place and recite the blessing a second time. (For the Tur rules according to Beit Shammai at the beginning of the eighth chapter, and the Rambam rules according to Beit Hillel. And see Tosafot 52b, starting with the words "Be-chulei".)

However, many wondered about the Tur: from where do we know to say that in a case of willful intent, if one recited the blessing not in his original place, he must recite the blessing a second time, for this is not clarified anywhere? For granted that he committed a transgression, nevertheless, since according to the Torah he certainly fulfilled his obligation just as in a case of inadvertence—for according to the Torah it is not relevant to distinguish between inadvertence and willful intent, as is understood. If so, you must say that the Rabbis decreed thus to distinguish between inadvertence and willful intent, that in a case of willful intent even ex post facto he has not fulfilled his obligation, and this is not found in the Gemara at all, nor did any of the Rishonim write thus. Therefore, even though there are some among the commentators who pressed themselves to uphold his words based on the discussion of the Shas, the matters are not at all compelling. And for the halacha, one should not recite the blessing a second time (Taz at the end of subsection 1 and Eliyah Rabbah). And anyone who is stringent in this is only among the bewildering, and causes blessings in vain (Eliyah Rabbah). And there is no difference between inadvertence and willful intent, for in both cases he should return to his place and recite the blessing, and if he did not do so but rather recited the blessing in his current place—he has fulfilled his obligation. And it has already been explained in siman 178 that matters requiring a blessing in their place have a law equal to bread, and therefore in these as well he is obligated to return to his place and recite the blessing even in a case of inadvertence. And it is possible that in these one may rely on the opinion of the Rambam that in a case of inadvertence he should recite the blessing in the place where he remembered, and so it appears to my humble opinion to be the primary view. (For this is like a double doubt: perhaps we hold like the Rambam, and if you should say like the Tur, perhaps only bread requires a blessing in its place. And although from the Magen Avraham subsection 6 it does not appear so, see there—nevertheless it appears so. And be precise and you will find it easy.)

Our teacher, the Beit Yosef, wrote in section 2: To what do these words apply? When he has no more bread. But if he has more bread – he should eat a little in the second place and bless, provided that he is not hungry from the first eating. Thus far his words. That is to say: even if he ate less than a kezayit there, nevertheless, since he finished the eating there – he may bless there, as I wrote in siman 178. However, this is according to the opinion of the Rosh. But according to the Rambam, it was explained there that he requires a blessing beforehand on what he will eat, and a retroactive blessing on what he ate; see there. And this is also the intention of our teacher, the Beit Yosef, for because he previously said "and if inadvertently, according to the Rambam he should bless in the place where he remembered, and according to the Ri and the Rosh he too must return to his place and bless" – to this he says: "To what do these words apply...". That is to say: for according to the Rambam he may indeed bless there, and according to the Ri and the Rosh it is resolved by his eating in the second place. And that which he wrote: "provided that he is not hungry from the first eating" is simple, for if a long time has already passed from his eating – Birkat HaMazon is no longer relevant. (And the words of the Magen Avraham, subsection 3, are not understood at all, as the Pri Megadim and the Machatzit HaShekel wrote; see there. And his primary difficulty is not a difficulty at all, for it is obvious that the Beit Yosef is referring to what was above according to the opinion of the Rosh. And know that if by the time he reaches his place the food will be digested – according to all opinions he should bless in the place where he remembered. Examine and you will find it simple.)

If one ate and does not know if he recited birkat hamazon or not, he must recite it due to the doubt because it is from the Torah, and a doubt regarding a Torah law is resolved stringently. This is specifically when he ate to the point of satiety, as it is written: "And you shall eat and be satisfied and you shall bless." However, if he did not eat to the point of satiety, his obligation is rabbinic, and a doubt regarding a rabbinic law is resolved leniently. And when he repeats it due to doubt—he also repeats the blessing of "ha-tov ve-ha-metiv" even though it is rabbinic; for since he became obligated—he became obligated in all of it, as such was the enactment, that every time one recites birkat hamazon he also recites "ha-tov ve-ha-metiv." Nevertheless, he cannot fulfill the obligation of another who ate and certainly did not recite the blessing, for a doubt does not discharge a certainty. And even though one who ate a rabbinic measure fulfills the obligation of one who ate a Torah measure, this is because he is a certainty in any event. But this is not the case when one recites the blessing due to doubt (see Sha'arei Teshuva in the name of the Pri Chadash, and such is the primary view). And see in section 9 what I wrote there.

Furthermore, it appears that specifically when he certainly ate, and it is a doubt whether he recited the blessing, he is obligated to recite the blessing. However, if there is a doubt whether he ate or did not eat, or if he ate and it is a doubt whether he ate bread or not – he does not recite the blessing. And the reason: for behold, seemingly it is not relevant in this case to say "it might enter your mind to say we follow the stringent view and he is obligated to recite the blessing," for behold, there is a corresponding leniency that if he already recited the blessing previously, his blessings now would be in vain. Rather, the matter is as follows: that when he certainly ate, and the obligation is certainly incumbent upon him to recite the blessing, therefore in a doubt regarding a Torah law you cannot exempt him from the obligation cast upon him. This is not the case if there is a doubt regarding the essence of his obligation; you cannot impose upon him to recite the blessing, for perhaps he is not obligated at all to recite the blessing, and his blessings would be in vain. (See Be'er Heitev, subsection 6, and I have written what appears correct in my humble opinion. Examine it and you will find it simple.)

Until when may one recite the blessing? Until the food in his innards is digested. And how much is the measure of digestion? As long as he is not hungry due to that eating (Gemara 53b). And from the time he begins to be hungry, even though it has not yet been completely digested, since it has begun to be digested—he no longer recites the blessing. And so too regarding drinking or the eating of fruits: if he is not thirsty or hungry for those fruits, even if he desires other fruits—he should recite the blessing when he is not expert enough to know if they have been digested. And in truth, it is difficult to estimate this, for the digestion is only the beginning of digestion, as the completion of digestion is a long time and not less than six hours, but rather the beginning of digestion (Magen Avraham, subsection 9). If so, who can estimate this? And all the more so regarding the eating of fruits and drinking. Aside from this, this measure is only relevant when he ate his fill, but if he ate a little—on the contrary, his desire increases further, and despite all this he is obligated to recite the blessing, and how much would the measure be in this case? (See Taz, subsection 2, and Magen Avraham, subsection 9.)

And behold, in the Gemara there it is stated that one who says the duration of digestion is the time it takes to walk four mil. According to the explanation of Rashi, for a large meal it is four mil, and according to the Tosafot, for a small meal it is four mil; see there. However, this is according to the one who holds there that the duration of digestion is as long as one is thirsty because of his eating. But according to that which we hold, that it is as long as one is not hungry, as I have written, there is no proof that he holds thus in any case; also, there is no proof that they disagree on this. Therefore, in truth, there is one who says so, that for a small meal it is four mil like the decision of our teachers, the Tosafot, and for a large meal, as long as one is not hungry because of his eating (Taz there). And the measure of four mil is an hour and twelve parts of an hour. Nevertheless, we still do not know how much is a large meal and how much is a small one. However, in any event, it is certainly true that up to four mil one must bless, and therefore there is no other way when one delayed more than this measure but to eat now a kezayit and recite Birkat HaMazon (Magen Avraham there). And so one must do, and likewise regarding the Bracha Acharona of other things. Except that in this case, if he diverted his mind—he must also recite the first bracha. And it appears to me in the general matter, when a person has a doubt whether he delayed the duration of digestion or not—regarding bread he must recite Birkat HaMazon, and regarding other things he should not bless due to the doubt (so it appears in my humble opinion).

The measure of eating to recite Birkat HaMazon is a medium-sized kezayit, and this is by rabbinic law. By Torah law, it is specifically enough to be satisfied (Magen Avraham, subsection 18). The Levush wrote that a kebeitzah is by Torah law, see there. There are some among the Rishonim who hold accordingly (the Ri, and the Ra'ah, and the Riv, as the Eliyah Rabbah wrote in subsection 9). However, most of our teachers do not hold accordingly, and more will be explained regarding this in siman 197 with the help of Heaven. (And know that regarding the law of a doubt whether one recited the blessing, where one is obligated to recite Birkat HaMazon as I have written, the law is the same for women. See Sha'arei Teshuva, subsection 7. Examine it and you will find it simple.)