A few nonharmonic tones occur in patterns of four or more pitches. The most common are successive passing tones, changing tones, and the pedal tone.
Successive Passing Tones
Two passing tones occasionally fill an interval of a fourth. In such cases both the passing tones may be unaccented (a) or they may be a combination of accented and unaccented passing tones (b).
Changing tones consist of two successive nonharmonic tones. The first leads by step from a chord tone, skips to another nonharmonic tone, and then leads by step to a chord tone (often the same chord tone). Other terms often used instead of changing tones are double neighboring tones or neighbor group. In many ways the two changing tones resemble neighboring tones with a missing (or perhaps implied) middle tone.
A pedal tone (also called a pedal point) is a held or repeated note, usually in the lowest voice, that alternates between consonance and dissonance with the chord structures above it. Thus, the dissonances are created by the moving chords above rather than the pedal tone itself. When a pedal tone occurs above other voices, it is called an inverted pedal tone.
Walther: Chorale Prelude on “Lobt Gott, ihr Christen, allzugleich” (“Praise God, Ye Christians, All Together”), mm. 10–13.