Reharmonization

Reharmonization is the practice of replacing the original chords of a tune with different chords while keeping the melody. It is a core creative skill in jazz arranging and composition.

Diatonic Substitution

The simplest form: replace a chord with another chord that shares most of its notes.

• iii for I: Em7 shares three notes with Cmaj7 (E, G, B). Use Em7 when you want a more ambiguous, less grounded tonic sound.
• vi for I: Am7 shares three notes with Cmaj7 (C, E, G). Creates a minor color under a major melody.
• ii for IV: Dm7 and Fmaj7 share three notes (F, A, C). The ii chord has stronger forward motion toward V.

The principle: chords a third apart share two or three notes and can substitute for each other.

Chromatic Approach Chords

Insert a chord a half step above or below the target chord. Before Cmaj7, play Dbmaj7 or Bmaj7 as a chromatic approach. This works because half-step resolution is the strongest motion in music.

Secondary Dominants

Precede any diatonic chord with its own V7. Before Am7 (vi), insert E7 (V7/vi). Before Dm7 (ii), insert A7 (V7/ii). This creates local ii-V motion that temporarily tonicizes each chord.

Tritone Substitution

Replace any dominant 7th chord with the dominant whose root is a tritone away. G7 becomes Db7. (See the dedicated doc on tritone substitution for full details.)

Coltrane Changes

John Coltrane's approach divides the octave into three equal parts (major thirds) and creates ii-V motion to each. The original ii-V-I in C becomes:

Dm7-G7 | Cmaj7 - Ebm7-Ab7 | Dbmaj7 (or E) - F#m7-B7 | Emaj7 (or Cmaj7)

This "giant steps" reharmonization creates constant modulation through three key centers.

Practical Process

Start with the melody. Every melody note must be a chord tone, extension, or acceptable tension of the new chord.

Maintain or improve voice leading. Good reharmonization creates smoother motion.

Preserve (or deliberately subvert) the harmonic rhythm.

Test by singing the melody over the new changes.

The goal is not to make harmony more "complex" but to find chords that illuminate the melody in new ways.