2. Question: If a person who isn’t sure whether he said birkas hamazon should say it again because this blessing comes from the Torah and when in doubt you have to be strict and say it again, yet the Shaarie Teshuva (Orach Chaim 184:4:1) says he cannot say birkas hamazon for others because we are only strict about fulfilling a Torah level doubt on a Rabbinic level so the person in doubt has a lower level obligation then the one who has a definite obligation to say birkas hamazon and can’t say it for the definite. However the Shulchan Aruch (Orach Chaim 197) says that one who ate a kazayis (olive bulk) of bread who has a rabbinic level obligation to say birkas hamazon can say birkas hamazon for a person who ate bread to satiation who has a Torah level obligation to say birkas hamazon, what’s the difference?
A. The parameters for obligating oneself to say birkas hamazon is the same regardless whether it’s because he is satiated or he ate a kazayis, the eating obligates the blessing.
B. The parameters that obligate a person to say bikas hamazon in doubt or definitely are different. Explain why and how that makes for a difference.
Answer: The obligation of one who definitely needs to say birkas hamazon stems from the fact he ate whether it was a kazayis or to satiation it is all the same thing but the obligation to say birkas hamazon in doubt stems from the fact that the rabbis said you should still say birkas hamazon even if you are in doubt so it is a separate type of obligation therefore one cannot say it for the other since they have different obligations.