Answering Amen
Our Sages (Yoma 37a) expounded the verse, “For I shall call out in the name of Hashem, give greatness to our G-d” that Moshe Rabbeinu told the Jewish nation that when I mention the name of Hashem, you show Him greatness. Our Sages (Sifri, Devarim 306) explain that this refers to answering Amen to any blessing where the name of Hashem is mentioned.
Indeed, we find that when King David recited the verse (in Chronicles I 16:36 and Tehillim 106) “Blessed is Hashem, G-d of Israel, from eternity to eternity,” the nation responded “Amen,” as the verse states, “And the entire nation said Amen.”
Our Sages (Shabbat 119b) spoke highly of the merit of answering Amen and said that anyone who answers Amen with all his might shall merit the gates of Gan Eden being opened before him, as the verse states, “Open the gates and let a righteous nation enter, who keeps faith” (“Emunim”), a reference to those who constantly answer Amen.
Obligatory or Optional?
Answering Amen is not merely a nice thing to do, rather, it is an actual obligation. In the words of Maran Ha’Shulchan Aruch (Chapter 215): “One who hears a Jewish person recite any blessing, even if one has not heard the entire blessing from beginning to end and even if one is not obligated to recite this blessing, must answer Amen.”
The language of the Shulchan Aruch is verbatim from the Rambam. Although others disagree and rule that answering Amen is not actually obligatory, the consensus of the Poskim is that it is indeed obligatory, in accordance with the ruling of the Rambam and Maran Ha’Shulchan Aruch.
Reciting Blessings Out Loud
The Chessed La’Alafim writes that it is particularly praiseworthy to recite blessings aloud in order to give others the opportunity to answer Amen. If one is among people he knows are not careful about answering Amen, it is preferable to recite blessings in an undertone. If there is a mixture of people present, some who are meticulous about answering Amen and others who are not, it is worthy to recite blessings aloud and whoever wishes can answer Amen.
Answering Amen While Reciting Something Ominous
Rabbeinu Yosef Haim writes in his Sefer Ben Ish Hai (Parashat Ki Tisa) that if one hears a blessing being recited while one is reciting the words “For they bow to nonsense and futility” within the Alenu Le’Shabeach prayer, one should not answer Amen to avoid appearing as though one condones idolatry, G-d-forbid.
Maran Rabbeinu Ovadia Yosef zt”l (in his Halichot Olam, Vol. 1, p. 247) questions the words of the Ben Ish Hai, for ultimately, Hashem knows full well that one meant to answer Amen to the blessing one heard and not to the words one was reciting. He adds that not answering Amen when necessary is a grave sin and proceeds to support this from the holy Zohar. Nevertheless, Maran zt”l rules that one should preferably stop a few words before or quickly recite the words “Va’anachnu Mishtachavim Lifnei Melech” when there is an impending Amen to be answered in order to avoid all concern.
Hearing a Blessing Over the Phone
If one hears a blessing being recited over the phone, the Acharonim rule that one should answer Amen (see Yechave Da’at Vol. 2, Ch. 68). Although some disagree, the Halacha follows the opinion that one must answer Amen.
