An Ashkenazi in a Sefardi Land
Question:
I daven using the Ashkenazi nusach, but sometimes I find myself in a non-Ashkenazi shul. How should I be davening, using the Ashkenazi nusach or the one of the shul? I've heard that Rav Moshe wrote a teshuva saying it may vary with the section of davening (e.g., pesukei dezimra vs. shemone esrei), but I'm not very familiar with it. Does the answer depend on whether it's Shacharis, Mincha, or Maariv? If I don't have an Ashkenazi siddur, but I remember pieces of the davening that are different from the shul's, should I try to say those or just say everything the way the shul says it, so that it's one consistent nusach and not a mixture? Should I make a point of bringing an Ashkenazi siddur with me? Does the answer vary if the shul davens Sefarad vs. Sefardi vs. Arizal/Chabad? Any guidance would be much appreciated.
Answer:
Any section that is said loud enough for others to hear (kedusha, for example), should be said according to the minhag of the shul you are in.
Parts that are said quietly to oneself (shemone esrei, for example) should be said in your own nusach.
As for things that are sometimes said loudly and sometimes quietly (birkos kerias shema, for example), it is best to say them according to the minhag of the shul so that you do not slip up and say your own nusach loudly. If you are concerned that you will be confused and will not be able to concentrate properly, you can use your own nusach for these sections. You should, however, be extra careful to say them quietly since they are sometimes said quietly and sometimes said loudly.
Therefore, in your situation, I recommend that you take a siddur off the shelf of the shul you enter and daven just as they do. It does not matter whether it is nusach Sefarad, Arizal, Eidot Hamizrach or Teimani. The only thing you should say in nusach Ashkenaz is the shemone esrei. You can use your own nusach for that, since it is silent. If you think you would stand out in the shul if you brought your own siddur to use for shemone esrei you can just say the shemone esrei as it is printed in the local siddur.
If you are the shaliach tzibbur, you should say your silent shemone esrei as you would the repeated shemone esrei, i.e., according to the local custom.
These principles apply to Shacharis, Musaf, Mincha and Maariv.
Rav Moshe Feinstein's teshuvos on the topic are in O.C., vol. 2, #23, 24, 104; O.C., vol. 4, #33, 34, 65; and O.C., vol. 5, #37.5.
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