Singing the prayer magen avot, the abbreviated repetition of Sabbath-eve amidah, is an old tradition which "goes back to the third century." Jewish communities in different parts of the world share the same mode for the prayer, though each community has its own variant. This mode, which, to Idelsohn, is the deepest expression of the Jewish soul, is based on an "original melodic line of Jewish folk song" and is also the foundation of various synagogue melodies (e.g. Leoni's yigdal). The mode is not exclusively Jewish; it is found in Arabic, "Syrian-Maronite," Old French and Catholic-German song. Idelsohn traces it in several European cultures and develops the hypothesis that it is a Semitic mode which was borrowed by the French from the Jews of France and penetrated German song and Gregorian chant. Since, however, the motives and spirit of the mode did not fit the development of French and German cultures, it gradually disappeared from their folk songs, but remained in a fossilized state in some Catholic chants. Part of the article deals with the nature of folk songs in general.