A question recently arose concerning a woman who ate a meal, with bread, but mistakenly recited the Beracha of "Al Ha’mihya" instead of Birkat Ha’mazon. She wondered whether she must recite Birkat Ha’mazon, or if perhaps she had fulfilled her obligation by reciting "Al Ha’mihya."
The basis for such a question is the nature of "Al Ha’mihya." This Beracha (as well as "Al Ha’etz" and "Al Ha’gefen") is often referred to as "Me’en Shalosh," which means that it is a brief, condensed text of the three primary Berachot of Birkat Ha’mazon. The Beracha of "Me’en Shalosh" incorporates the themes of the first three Berachot of Birkat Ha’mazon, which are required on the level of Biblical obligation. There is thus room to consider the possibility that if one mistakenly recited "Al Ha’mihya" when he was to have recited Birkat Ha’mazon, he has fulfilled his obligation, albeit on the level of "Be’di’abad" (after the fact, as opposed to the optimal standard of Misva observance).
This issue is subject to debate among the Halachic authorities. The Ra’a (Rabbi Aharon Halevi, Spain, 13th century), in his Hilchot Berachot – Pekudat Ha’leviyim (listen to audio recording for precise citation), writes explicitly that one who recites "Al Ha’mihya" instead of Birkat Ha’mazon has fulfilled his obligation. It has been noted that this may also have been the view of the Shulhan Aruch. In a different context, the Shulhan Aruch cites several different opinions among earlier authorities in defining the term "Pat Ha’ba’a Be’kisnin," a category of foods over which one recites "Mezonot" before eating and "Al Ha’mihya" after eating. The Shulhan Aruch writes that since this issue is subject to debate, we follow all views, and if a food meets any of these definitions, it requires "Mezonot" before eating and "Al Ha’mihya" after. Interestingly, although this is clearly a situation of "Safek" (a Halachic uncertainty), the Shulhan Aruch rules that over such foods one would recite "Al Ha’mihya." Rather than requiring reciting Birkat Ha’mazon in case this food does not meet the criteria of "Pat Ha’ba’a Be’kisnin," and it is considered bread, the Shulhan Aruch rules that in such situations one recites "Al Ha’mihya." This ruling would appear to assume that the recitation of "Al Ha’mihya" satisfies the Biblical requirement of Birkat Ha’mazon. This is also the view of the Ginat Veradim (Kelal 1, Siman 24).
Others, however, disagree. The Ritba (Rabbenu Yom Tob Ben Abraham of Seville, Spain, 1250-1330), in his commentary to Masechet Berachot (listen to audio recording for precise citation), writes explicitly that whenever one is required to recite Birkat Ha’mazon, he does not satisfy this requirement by reciting "Al Ha’mihya." This view is followed by numerous later authorities, including the Bah, Elya Rabba, Erech Ha’shulhan, Perah Shushan and Hayeh Adam.
As for the final Halacha, we follow the basic Halachic principle of "Safek Berachot Le’hakel," which means that one should not recite a Beracha if it is uncertain whether the Beracha is warranted. In the case under discussion, then, since some authorities maintain that one fulfills the Birkat Ha’mazon requirement by reciting "Al Ha’mihya," one should not recite Birkat Ha’mazon, and should instead rely on his recitation of "Al Ha’mihya." However, Rabbi Moshe Halevi (Israel, 1961-2001), in his work Birkat Hashem, writes that in certain circumstances, it is preferable to wash and eat more bread so that one will be required to recite Birkat Ha’mazon. If in the original meal the person ate the amount of "Sebi’a," meaning to the point of satiation, then he is required to recite Birkat Ha’mazon on the level of Torah obligation. And since, as we saw, some authorities maintain that one does not fulfill this obligation by reciting "Al Ha’mihya," it is preferable to satisfy all views by eating more bread to obligate oneself in Birkat Ha’mazon, rather than risk neglecting a Torah obligation. It should be noted, however, that this is required only on the level of "Humra" (added stringency). According to the strict Halacha, one does not recite Birkat Ha’mazon and does not have to eat more, as discussed above.
In the case of a woman, there is even greater room for leniency, because it is not certain that women are obligated in the Misva of Birkat Ha’mazon on the level of Torah law (though they are clearly obligated, at least on the level of Rabbinic enactment). Certainly, then, if a woman mistakenly recited "Al Ha’mihya" instead of Birkat Ha’mazon, then she does not have to eat more bread to obligate herself in Birkat Ha’mazon.
Summary: If a person mistakenly recited "Al Ha’mihya" instead of Birkat Ha’mazon, he has fulfilled his obligation, and does not have to recite Birkat Ha’mazon. However, if he had eaten to the point of satiation (such that he is obligated in Birkat Ha’mazon on the level of Torah law), it is preferable for him to wash again and eat more bread, to obligate himself in Birkat Ha’mazon and thereby satisfy all opinions.
