Q. May a cantor use melodies that come from popular musical shows?
A. Within reason and judiciously. The history of liturgical music is varied; some of our favourite melodies, such as Ma’oz Tzur and Adir Hu, came into Judaism from folk songs, and on the other hand some synagogal hymns have lent their tunes and even their lyrics to songs you hear at weddings and Bar/Bat-Mitzvah celebrations. We have probably all heard operatic arias and even snatches from shows like “Phantom of the Opera” in the K’dushah.
The main principle is that the dignity of the service must not be compromised or cheapened. It goes without saying, though, that melodies composed for and/or used in the worship services of other religions must not be used in the synagogue.