In the Brachah of Yishtabach

Birchos hashachar k'halachah: Aloud, with kavanah, bechavrusa

Derech Emunim

The Halachos of Answering Amen

In the brachah of Yishtabach, as long as one has not started Baruch Atah Hashem, he answers amen to every brachah except for amen to the brachos of Baruch She’amar and Yishtabach.

But it is worthy to be careful not to come to point where one is obligated to answer amen while in the middle of saying the praises in the brachah of Yishtabach, so as not to need to stop in the middle of saying them. After beginning Baruch Atah Hashem, one should not answer amen until the end of the brachah, but there is an opinion that differs about this din.

1. Mishnah Berurah 51 2. The Biur Halachah (ibid) explained that this brachah begins right from the first word, Yishtabach, and not with Baruch Atah Hashem later on in the brachah. The brachah of Yishtabach is considered a brachah that begins with Baruch, because it is a brachah hasemuchah lechavertah, a brachah that is adjacent to another one, and as the Tosafos writes (Pesachim 104b, ad loc. Chutz) that it is considered adjacent to the brachah of Baruch She’amar, and that exempts it from beginning with Baruch (as ruled by the Shulchan Aruch 54 1). Therefore, as soon as one begins Yishtabach, one should not answer amen after the brachos of Baruch She’amar and Yishtabach, which are not mentioned in the Talmud, but after the other brachos, one may answer amen even in the middle of the brachah (See Ishei Yisrael, Ch. 16, comment 15).
2. However, the Ketzos Hashulchan wrote (18:2, and ibid in Badei Hashulchan, 5) that as long as he did not say Baruch Atah Hashem in the brachah of Yishtabach, the din is not like someone who is in the middle of a brachah and he may answer amen also to brachos that do not appear in the Talmud, similar to one who is saying Pesukei Dezimrah. He explains that although the brachah of Yishtabach is considered semuchah lechavertah still, as long as one does not start to say Baruch Atah Hashem, it is not considered as if he is in the middle of a brachah with regard to answering amen after the brachos. (And see Shu"t Shaarei Yosher, 18:2).
3. The poskim wrote (see Mishnah Berurah 53 1) that in the first part of the brachah of Yishtabach, there are 15 terms of praise mentioned, from Shir Ushevachah until Brachos Vehoda’os. But the holy Zohar (Terumah 132 1) says that this part has only thirteen praises, because the words "brachos vehoda’os" belong to the rest of the brachah and are not included in the praises (see Be’er Heitev, ibid 1). The Magen Avraham (beginning of siman 53) wrote that one should say these praises in one breath, but the Mishnah Berurah (ibid) ruled that it is not necessary, but in any case, they should be said continuously, and there should be no hefsek while saying them.
4. The Ben Ish Chai (Vayigash 15) wrote that one who is up to the first part of the brachah of Yishtabach, before the praises, and he sees that the chazzan is about to say Kaddish, he should hold off saying the praises and answer amen. Then he should say the praises without stopping. The Kaf Hachaim (53 2) concurs. And see Ben Ish Chai (ibid) who wrote that if it happens that while he is saying the praises he heard Kaddish, he should stop and answer, and then go back and repeat from "Ki Lecha na’eh" so that he should say the praises without a hefsek. But Likutei Mahari"ch (Nusach Birchas Yishtabach) wrote that one must not stop to answer amen in the middle of saying the praises.
5. The Mishnah Berurah (54 3) asked whether the part of the brachah from "Baruch Atah Hashem" until the end of the brachah is like a "brachah ketzarah" where one must not stop even to say Yehei Shemei Rabbah and Kedushah, or if it is like a brachah arukah, and he left it that it needs further study. But the Ketzos Hashulchan (ibid) wrote that it seems that the halachah of this part is like a brachah ketzarah when one should not answer amen. Sefer Ishei Yisrael (Ch. 16:17) cited Harav Chaim Kanievsky, that one who is up to this part of the brachah should not stop to hear or answer to Kaddish that the shat"z says after Yishtabach, but rather should continue to recite the brachah until the end.