Ordinary Auxiliary Notes
Auxiliary notes are non-chord notes which are approached and quit in the opposite direction by step. They are usually unaccented.
Auxiliary notes occur between two chord notes which are the same. They can either be upper or lower auxiliary notes.
Version A is undecorated. Version B uses an upper auxiliary note between the two alto Gs; version C uses a lower auxiliary note.
Auxiliary Harmony Notes
Auxiliary harmony notes are decorative chord notes which belong to the current chord. They can be accented or unaccented.
Don’t confuse auxiliary harmony notes with ordinary auxiliary notes. Ordinary auxiliary notes are non-chord notes. Auxiliary harmony notes fit with the chord, and are used to create rhythmic movement/interest.
In this example, the alto and bass notes in the first box are auxiliary harmony notes. They are decorative notes which still belong to the current chord of G major. In the second box, the soprano and alto notes D and F# are auxiliary harmony notes in the chord of D major.
