121. Modim

20:5 When the shaliach tzibbur reaches Modim, the entire congregation bows and says the “Modim d’Rabbanan.” (The Kitzur Shulchan Aruch says to say the entire prayer while bowing but Mishnah Brurah 127:5 and Biur Halacha on OC 127:1 acknowledge the universal custom to bow for the first three words and then to straighten up.) What if someone is still reciting their personal Shemoneh Esrei and he hears the shaliach tzibbur say “modim…?” If he is in the middle of a blessing, he should bow. If he is at the beginning or end of a blessing, then he does not bow. This is because one may not add bows at the beginning or end of a blessing beyond those that were instituted by the Sages. 20:6 Before saying Sim Shalom, the shaliach tzibbur adds birkas kohanim, the priestly blessings. The congregation replies “kein y’hi ratzon” (May such be His will) rather than “Amen” at the end of these blessings. Birkas kohanim is only said at shacharis and musaf; on fast days, when Sim Shalom is said instead of Shalom Rav, birkas kohanim is also said at mincha. It is not said in a Shiva house or on Tisha b’Av morning.