Plagal key

Plagaltonarten ( "derived" keys ) are derived from the authentic Kirchentonarten derived by this to a fourth downward offset are. In contrast to the authentic modes, the plagal modes can be recognized by the prefix “Hypo-” (ancient Greek under- ).

Authentic and plagal church modes (modes) have the same finalis , but differ in their ambitus and their repercussa : this is a third lower in the plagal modes than in the authentic ones. It should be noted that h (as part of the unstable tritone  fh) is avoided and replaced by c ¹ .