Filling parts
Parts that are not led independently melodically but only complete the harmony.
What it means
Filling parts (Füllstimmen) are voices of a multi-part texture that have no independent melodic task but complete the harmony and fill out the sound. They usually follow the outer voices, stay in narrow paths, and often consist of held notes, repetitions, or plain chord tones.
Musical use
Filling parts occur in orchestral writing, for instance in violas or second horns that hold chord tones, and in four-part choral writing, where inner voices complete the harmony. In figured-bass practice the players themselves fill out the chords above the bass with filling parts. Although inconspicuous, they contribute decisively to the fullness and tone color of a texture.
Filling parts should be distinguished from principal parts, which carry the melody or countermelody, and from accompanying parts, which play rhythmically independent figures. They also differ from inner voices in the wider sense: inner voices can be melodically independent, filling parts are not.
Performance practice
If you play a filling part, hold back in sound and provide even, calm notes, since the task is support and coloring, not foreground. Listen to the principal part and adapt volume and intonation so that the chords sound cleanly together.