plagal mode

In music, a plagal mode is a type of church mode that is a variation of an authentic mode. Authentic modes begin and end on a specific note called the finalis, while their corresponding plagal modes range from a fourth below to a fifth above this finalis. The finalis of the authentic mode also serves as the final note for its plagal counterpart. This system, derived from ancient Greek musical concepts, was foundational in medieval and Renaissance music. The plagal cadence, a harmonic progression where the subdominant triad leads to the tonic triad (IV–I), is often associated with the final "amen" in Christian hymns.1234