8. Answering Amen:

Initially it is an absolute obligation for one to answer Amen to a blessing that he hears, even if he does not have intent to fulfill his obligation with that blessing as explained in length in Chapter 5 Halacha 1, and certainly if he does.

Bedieved if did not answer Amen:[1] Bedieved, if one listened to a blessing with intent to be Yotzei but did not answer Amen, he nevertheless fulfills his obligation.

• Example: If someone recites a blessing over bread and you are listening with the intention to partake in the blessing, you should say “Amen” after their blessing. If you forget to say “Amen,” you are still considered to have fulfilled your obligation to hear the blessing.

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[1] Admur 213:4; [See also Admur 8:11; 104:5; 124:6; 201:5] Michaber 213:2; Rambam Brachos 1:11; Brachos 45b