During the Baroque Era, the “Rule of the Octave” was a practical tool that enabledmusicians to gain harmonic flexibility at the keyboard.5 The rule prescribed how toharmonize a scale in the bass using stylistic tonal progressions. In jazz, a similar rule canalso be developed. Instead of placing the scale in the bass, the major scale is placed in thesoprano voice. The jazz rule of the octave explains how to harmonize a descending majorscale with idiomatic jazz progressions. By examining different harmonic outcomes, therelationship of melodies to chords and chords to melodies becomes clear. The jazz ruleof the octave also helps us to realize the harmonic potential of different melodic segmentsand examines their behavior in the context of underlying chord progressions. Figures21.3a–21.3d illustrate four distinct harmonizations of the descending major scale