Tonstufen
Tonstufen are the individual degrees of a musical scale, counted from the tonic as Stufe I up to Stufe VII in diatonic systems. They describe the vertical pitch positions that form the scale, and they serve as the basis for analyzing harmony and melody in tonal music. Each Tonstufe has characteristic interval relations to the tonic and often bears a conventional function within a key.
In a major scale, the seven Tonstufen are I (tonika), II (supertonika), III (mediante), IV (subdominante), V
Tonstufen are central to roman-numeral analysis, where each degree signs the harmonic function: tonika (I, vi
Beyond the common major and natural minor, the concept applies in other diatonic modes and in pedagogy