The Talmud poses the question of whether the obligation of Birkat HaMazon, stated in the Mishnah, is of biblical or rabbinic origin. According to Rashi (s.v. oh) and the Rosh (3:13), the question is prompted by the crucial issue of the assignment of land ownership in the land of Israel, an integral theme of Birkat HaMazon. Tosafot (s.v. nashim) disagree, noting that that issue would affect the obligation of kohanim and levi’im as well. Rather, they suggest, the crucial issue is that of Brit and Torah, indispensable components of Birkat HaMazon. The Tur (O.C. 186) cites the Ra’avad as obligating women biblically; however, the Rambam (Hil. Berakhot 5:1) and Tosafot consider the point an unresolved issue, and thus designate the obligation as one of safek. (See Resp. Halikhot Sheba, 6).

The Shulchan Arukh (O.C. 187:9) rules that while a man who omits “Brit V’Torah” from Birkat HaMazon does not fulfill his obligation, a woman who does so does. The Rama writes that women should omit this section, although the practice is that women do recite this section (see Magen Avraham, 187:3, and Arukh HaShulchan, 187:8, for explanations why this is; see also Resp. Riv’vot Ephraim, VIII, 164).

The Talmud explains the relevance of the question of biblical or rabbinic obliagation as being the issue of whether a woman can discharge the obligation of a man who listens. However, it would seem that another relevant issue would be the question of a woman who is unsure if she has recited Birkat HaMazon. A man in that situation would be obligated to recite the Birkat HaMazon, due to its biblical obligation. The Chayei Adam (klal 47:2) applies this rule to women as well (unless she did not eat to satiety, which is required for a biblical obligation). The Resp. Binyan Shlomo (I, 13) exempts women from repeating Birkat HaMazon in this situation, due to a sfek-sfeika; she may have indeed recited Birkat HaMazon, and she may not be biblically obligated. Many later authorities share this view. The Tzlach, however, wonders why this issue was not suggested by the Talmud as the relevant outcome of its inquiry (see Chesed Yitzchak, 3).