finalis

…furnishes the first step, or finalis, for each of the four modal pairs, authentic and plagal. Whereas authentic modes begin and end with the finalis, their plagal partners range from the fourth below to the fifth above the finalis. Each mode, however, is characterized not only by its finalis but…

…modes are classified by their finalis, the usual final note of a melody in that mode. Each of the four notes of the tetrachord D–E–F–G serves as the finalis of an “authentic” mode (see chart below).