308. One Who Bentched On His Own

45:16 If three ate together and one of them forgot and bentched on his own (or even did so intentionally – Bi’ur Halacha 194:1 s.v. “shachach”), the other two can still form a zimmun after he finishes. Even though he already bentched, he should respond “Blessed is the One of Whose bounty we have partaken.” However, if he already participated in a zimmun with two other diners, he may no longer join with these two in a zimmun. If two of the three forgot to wait and bentched, a zimmun may no longer be formed. (See Bi’ur Halacha 194:1 s.v. “echad meihem” for cases such as three out of ten, two out of four, four out of six, etc. Generally speaking, if two diners of a group are left, a third diner who already bentched may join them to form a zimmun.)

45:17 If three ate together and two of them have already finished and want to bentch, but the third is still eating, he must stop in order to form the zimmun. He responds and thereby fulfills his obligation in zimmun. He should wait until the leader has finished the first bracha of bentching, after which he may resume eating. In such a case, he does not say a bracha before eating because his intention was to continue. When he’s finished eating, he bentches on his own. If only one diner is ready to bentch, the other two do not have to stop eating for the sake of the one, though they may if they wish to accommodate him. If ten ate together, four diners must stop eating to answer bentching for six who are ready. In this case, they only have to wait until they have said “Blessed is our God, of Whose bounty we have partaken.” When the four finish eating, they then form a zimmun without mentioning God’s Name.