A
musical system developed during the time of
Pope Gregory the Great, hence Gregorian, to which countless amounts of
church music has been set. The roots of German
chorale singing, and thus J.S.
Bach, can also be traced to it.
It has seven regular tones and a Tonus Peregrinus (Wandering Tone).
Also, even though it is supposed to be sublime in many ways, aesthetic concerns are somewhat secondary. In fact, it is very functional, and relatively easy to learn, since in its pure form it can accompany singing in virtually any language.