Reharmonization is the art of keeping the melody while changing the chords underneath. It's one of the oldest creative practices in Western music - Bach reharmonized chorales, Beethoven reharmonized his own themes in development sections, and jazz musicians have made it a defining characteristic of the art form. When Bill Evans played Autumn Leaves, the chords weren't quite what Victor Young wrote. They were richer, stranger, more personal. That's reharmonization: same song, your harmony.
JMove's suggestion engine contains fourteen reharmonization techniques. Each one is a window into a different era, a different school of thought, a different way of hearing how chords relate to each other. They're not AI guesses or statistical patterns from a dataset. They're rules - codified from theory textbooks, transcriptions, and decades of harmonic practice. Every suggestion comes with a name you can look up and a reason you can understand. What follows is every technique, in full detail: the history, the theory, the algorithm, and the sound.
1. Tritone Substitution
The tritone substitution is the Swiss Army knife of jazz harmony. Take any dominant seventh chord and replace it with the dominant seventh chord a tritone (six semitones) away. G7 becomes Db7. The reason this works is beautiful in its simplicity: both chords share the same tritone interval - the pair of notes that creates all the tension. In G7, the tritone is B and F (the third and seventh). In Db7, the tritone is F and Cb (enharmonically B). Identical tension. Different bass note. And that different bass note is the magic - Db resolves to C by half step instead of by fifth, creating a chromatic bass line that sounds sophisticated and inevitable.
Dizzy Gillespie and the bebop musicians of the 1940s made tritone substitution a standard part of the jazz vocabulary. It's the reason bebop sounds so chromatic - all those flatted fifths and sharp elevens are tritone substitutions heard from different angles. Once you hear it, you hear it everywhere: in Cole Porter, in Jobim, in every jazz pianist who ever turned a ii-V-I into ii-bII7-I.
The algorithm is precise: find the root's position in the chromatic scale, add six semitones (mod 12), and build a dominant chord on the result. Crucially, JMove preserves the original chord's extensions - G7#9 becomes Db7#9, not plain Db7. The altered tensions are part of the color, and flattening them to a basic seventh would lose half the point. The engine produces both individual substitutions (replace one dominant at a time) and a batch variant that replaces every dominant in the progression simultaneously, creating maximum chromatic saturation.
Example: Dm7 - G7 - Cmaj7 → Dm7 - Db7 - Cmaj7
Bass motion: D → G → C (fourths)
vs: D → Db → C (chromatic descent)
Both resolve. The second one glides.2. Modal Interchange
Modal interchange - sometimes called modal mixture or borrowed chords - is the practice of borrowing chords from the parallel key. If you're in C major, you can reach into C minor and borrow its chords: Fm7 instead of Fmaj7, Abmaj7 instead of Am7, Bb7 instead of G7, Ebmaj7 instead of Em7. Each substitution adds a darkness, a shadow, that the major key alone can't provide.
The technique is ancient. Bach borrowed chords from parallel keys constantly - the Picardy third (ending a minor-key piece on a major chord) is modal interchange in its simplest form. Schubert was obsessed with the sudden shift between major and minor, sometimes within a single phrase. The Beatles used it so naturally that most listeners never notice: the bVII chord in "Let It Be" (Bb in the key of C) is a modal interchange from Mixolydian. Radiohead built entire albums on the ambiguity between parallel modes.
In jazz, Wayne Shorter took modal interchange further than almost anyone. Compositions like "Speak No Evil" and "Footprints" live in a space where major and minor coexist simultaneously, where borrowed chords aren't visitors but permanent residents. The result is harmony that feels like sunlight passing through stained glass - the same light, fractured into unexpected colors.
In C major:
Fmaj7 (IV) → Fm7 (iv) — borrowed from C minor
Am7 (vi) → Abmaj7 (bVI) — borrowed from C minor
G7 (V) → Bb7 (bVII) — borrowed from C minor
Em7 (iii) → Ebmaj7 (bIII)— borrowed from C minor
Example: Cmaj7 - Am7 - Fmaj7 - G7
→ Cmaj7 - Abmaj7 - Fm7 - Bb73. Coltrane Changes
In 1959, John Coltrane recorded "Giant Steps" - a composition that divided the octave into three equal parts using major third intervals. The progression cycles through three key centers separated by major thirds (B, G, Eb), moving so rapidly that conventional bebop improvisation simply collapses. Tommy Flanagan, one of the finest pianists of his generation, famously stumbled during his solo on the original recording. The harmony was that new.
What Coltrane had discovered was a symmetrical subdivision of the octave. Twelve semitones divided by three gives four semitones - a major third. Three major thirds (C → E → Ab → C) traverse the entire chromatic space and return home. Each key center gets its own ii-V approach, creating a cascade of resolutions that sounds both mathematically precise and emotionally overwhelming. It's harmony as geometry.
As a reharmonization technique, Coltrane changes replace a dominant chord with movement through the major-third cycle. The algorithm takes the root, adds four semitones (first substitution) or eight semitones (second substitution), and builds a dominant chord on each. G7 can become B7 (major third up) or Eb7 (two major thirds up, enharmonically a major third down). The engine applies this only to dominant chords and produces separate variants for each distance, letting you choose how far into the kaleidoscope you want to go.
G7 → B7 (root + 4 semitones, major third up)
G7 → Eb7 (root + 8 semitones, two major thirds up)
The full Coltrane cycle from C:
C → E → Ab → C (three major thirds = full octave)
Applied to a ii-V-I in C:
Dm7 - G7 - Cmaj7
Dm7 - B7 - Cmaj7 (first substitution)
Dm7 - Eb7 - Cmaj7 (second substitution)4. Secondary Dominant
A secondary dominant is a V7 chord that temporarily tonicizes a non-tonic chord - it creates a fleeting sense of arrival on a chord that isn't the home key. The concept predates jazz by centuries. Bach used secondary dominants in virtually every chorale harmonization. When you hear a D7 resolve to G in the key of C, that D7 is V7/V - the "five of five." It borrows the gravitational pull of the dominant-tonic relationship and applies it to a chord that isn't the tonic.
Jerome Kern, Cole Porter, and the great American songbook composers used secondary dominants to create harmonic momentum within otherwise diatonic progressions. The bridge of "All The Things You Are" is essentially a chain of secondary dominants, each one pulling the harmony into a new momentary key center before the real resolution arrives.
The algorithm identifies diatonic target chords (ii, iii, IV, vi) and inserts their V7 before them. The secondary dominant's root is calculated as a perfect fifth above the target - seven semitones up in the chromatic scale. The engine deliberately skips V7/I (which would just be the regular dominant, creating confusion rather than color) and V7/V (which is already so common that inserting it feels redundant rather than creative). This is an expansion technique - it adds chords to the progression rather than replacing existing ones.
In C major:
Target Dm7 (ii) → insert A7 (V7/ii)
Target Em7 (iii) → insert B7 (V7/iii)
Target Fmaj7 (IV)→ insert C7 (V7/IV)
Target Am7 (vi) → insert E7 (V7/vi)
Example: Cmaj7 - Dm7 - G7 - Cmaj7
→ Cmaj7 - A7 - Dm7 - G7 - Cmaj75. Backdoor ii-V
The standard ii-V-I is jazz's most fundamental cadence: Dm7-G7-Cmaj7. The V7 approaches the tonic from a fifth above. But there's another way home - the backdoor. Instead of G7 resolving down a fifth to C, you approach from a whole step above: Bb7 to Cmaj7. The resolution is softer, more unexpected, like entering your house through the garden instead of the front door.
Tadd Dameron was the master of the backdoor resolution. His compositions are full of moments where the harmony seems headed one direction and then arrives home from the other side. The full backdoor ii-V adds the iv chord before the bVII7: Fm7-Bb7-Cmaj7. It's a complete cadence from the subdominant side - the minor iv chord provides the darkness, the bVII7 provides the pull, and the resolution to I feels both surprising and completely right.
The algorithm detects dominant chords that resolve down a fifth to the next chord (the standard V-I motion) and offers two variants. The simple variant replaces the V7 with the bVII7 chord - root calculated as two semitones below the target (or ten semitones above, mod 12). The full variant inserts the iv-m7 before it, creating the complete backdoor approach. The iv chord's root sits five semitones above the target.
Standard: Dm7 - G7 - Cmaj7 (V7 → I, down a fifth)
Simple: Dm7 - Bb7 - Cmaj7 (bVII7 → I, down a whole step)
Full: Dm7 - Fm7 - Bb7 - Cmaj7 (iv-m7 - bVII7 → I)
The front door: G → C (descending fifth)
The back door: Bb → C (ascending whole step)6. Passing Diminished
The diminished seventh chord is one of the most versatile sounds in harmony. Four notes, all equidistant (minor thirds), creating a symmetrical structure that belongs to no single key. Because of this symmetry, a single dim7 chord can resolve in four different directions - each of its four notes can function as a leading tone. This ambiguity made it a favorite of Romantic-era composers. Chopin used diminished chords as chromatic connectors. Liszt used them as harmonic trapdoors, dropping the listener into unexpected keys.
In jazz, the passing diminished chord serves a specific connective function: it bridges two chords whose roots are a whole step apart. If the bass moves from C to D (a whole step), you can insert a C#dim7 between them. The bass now moves C-C#-D: three chromatic half steps instead of one whole step. The diminished chord doesn't replace anything - it fills a gap, creating smooth chromatic motion where there was a jump.
The algorithm scans consecutive chord pairs and measures the interval between their roots. When it finds a whole step (two semitones ascending or ten semitones descending), it inserts a dim7 chord on the chromatic note between them. For ascending motion (C to D), the passing chord root is one semitone above the first root (C#dim7). For descending motion (D to C), the passing chord root is one semitone below the first root (Dbdim7). The diminished chord's symmetric nature means the specific spelling is less important than the chromatic voice leading it creates.
Ascending whole step (gap = 2 semitones):
Cmaj7 - Dm7 → Cmaj7 - C#dim7 - Dm7
Bass: C → D → C → C# → D
Descending whole step (gap = 10 semitones):
Dm7 - Cmaj7 → Dm7 - Dbdim7 - Cmaj7
Bass: D → C → D → Db → C7. Upper Structure Triads
Upper structure triads are one of the most colorful tools in modern jazz harmony. The idea is simple but the effect is radical: take a dominant seventh chord and stack a major triad on top of it. The triad isn't random - specific triads placed over specific dominants produce specific extended colors. The result is a chord that sounds simultaneously grounded (the dominant bass) and floating (the triad voicing above).
Herbie Hancock made upper structures a signature part of his harmonic vocabulary. Listen to his work with Miles Davis on "Maiden Voyage" or his solo albums like "Empyrean Isles" - those thick, crystalline voicings that seem to contain two chords at once are upper structure triads. McCoy Tyner used them percussively, stacking fourths and triads over pedal tones to create the massive, modal sound that defined 1960s spiritual jazz.
JMove's engine produces two upper structure variants. US II places a major triad on the ninth of the dominant - for G7, that's an A major triad (A-C#-E) over the G bass, producing the extensions 9-#11-13. This is the Lydian dominant color: bright, open, with that characteristic raised eleventh that floats above the chord like a halo. US bVI places a major triad on the flat thirteenth - for G7, that's an Eb major triad (Eb-G-Bb) over the G bass, producing b13-1-#9. This is the altered dominant color: dark, tense, with the sharp nine and flat thirteen that scream for resolution.
US II (bright, Lydian dominant):
G7 → G13#11
Triad: A major (root + 2 semitones)
Tones over G: A(9) - C#(#11) - E(13)
US bVI (dark, altered dominant):
G7 → G7alt
Triad: Eb major (root + 8 semitones)
Tones over G: Eb(b13) - G(1) - Bb(#9)
Same dominant root. Two completely different emotional worlds.8. Scale Family Substitution
Allan Holdsworth thought about harmony differently from almost every other guitarist who ever lived. Where most musicians start with a chord and ask "what scale fits?", Holdsworth started with a scale and asked "what chords live inside it?" He called these groups "chord families" - siblings that share the same parent scale. From a single D Dorian scale (D E F G A B C), you can extract Dm7, Em7, Fmaj7, G7, Am7, Bm7b5, and Cmaj7. They're all children of the same seven notes. Any of them can substitute for any other without introducing a single note that wasn't already in the scale.
This is a fundamentally different way of hearing substitution. Traditional functional harmony asks "what role does this chord play?" (tonic, subdominant, dominant). Holdsworth's approach asks "what family does this chord belong to?" The families overlap - a chord can have multiple parent scales, and therefore multiple families of siblings. The result is a web of relationships far richer than the functional tonic-subdominant-dominant trichotomy.
The algorithm takes a chord, identifies every parent scale that contains its tones, extracts all sibling chords from those scales, and ranks them by voice-leading distance - how much total motion is required to move from the original chord to the substitute. The closer the voice leading, the higher the score. A substitution that requires only one voice to move by a half step scores near 0.70. A substitution that requires every voice to jump scores near 0.30. The engine caps the output at the top two families and three siblings per family, keeping the suggestions focused rather than overwhelming.
Chord: Dm7
Parent scale: C major (D Dorian)
Siblings: Em7, Fmaj7, G7, Am7, Bm7b5, Cmaj7
Score = max(0.30, 0.70 - voice_leading_distance × 0.03)
Close siblings (smooth voice leading) score high.
Distant siblings (large jumps) score low.
Holdsworth heard the family. The algorithm maps it.9. Diatonic Substitution
Diatonic substitution is the textbook approach - replace a chord with another chord that serves the same harmonic function. The concept comes from the Berklee College of Music's function family system, which groups all seven diatonic chords into three families based on their shared tones and tendency to resolve in similar ways.
The tonic family contains I, iii, and vi - all chords that share enough tones with the tonic triad to provide a sense of arrival or stability. In C major, that's Cmaj7, Em7, and Am7. You can replace Cmaj7 with Am7 and the music still feels "at rest," just with a different shading. The subdominant family contains ii and IV - Dm7 and Fmaj7 - both of which pull gently away from the tonic toward the dominant. The dominant family contains V7 and vii° - G7 and Bm7b5 - both of which contain the tritone (B-F) that creates the strongest pull back to the tonic.
These substitutions are the safest in the engine - they preserve harmonic function exactly. A tonic chord replaces a tonic chord. A dominant replaces a dominant. The melody always works because the underlying function hasn't changed. It's like translating a sentence into a different register of the same language: the meaning is identical, the flavor is different. Jazz arrangers use diatonic substitution constantly when writing for big bands, creating harmonic variety within a chorus without ever disturbing the fundamental architecture of the tune.
Function families in C major:
Tonic: Cmaj7 (I) ↔ Em7 (iii) ↔ Am7 (vi)
Subdominant: Dm7 (ii) ↔ Fmaj7 (IV)
Dominant: G7 (V) ↔ Bm7b5 (vii°)
Example: Cmaj7 - Dm7 - G7 - Cmaj7
→ Am7 - Fmaj7 - Bm7b5 - Em7
Same function. Different color. Melody untouched.10. Diminished Substitution
This technique is distinct from the passing diminished (technique 6). Where the passing diminished inserts a new chord between existing ones, diminished substitution replaces a dominant seventh chord with a dim7 chord built one semitone above its root. The reason this works is that the dim7 chord shares three of its four notes with the dominant it replaces.
Consider G7: G-B-D-F. Now consider Abdim7: Ab-B-D-F. Three notes are identical (B, D, F). The only difference is the root - G becomes Ab. But functionally, an Abdim7 is almost indistinguishable from a G7b9 without the root. The Ab is the b9 of G. So replacing G7 with Abdim7 is essentially playing a rootless G7b9 - one of the most common dominant sounds in jazz. The substitution is nearly invisible to the ear but changes the texture subtly, replacing the dominant's assertive bass with the diminished chord's rootless ambiguity.
G7: G - B - D - F (root, 3, 5, b7)
Abdim7: Ab - B - D - F (root + 1 semitone, then dim7)
Shared tones: B, D, F (3 out of 4)
The Ab is the b9 of G.
Abdim7 ≈ G7b9 without the root.
Example: Dm7 - G7 - Cmaj7 → Dm7 - Abdim7 - Cmaj711. Chromatic Bass Line
A chromatic bass line is one of the most satisfying sounds in music. When the lowest voice moves by half steps - ascending or descending - it creates a sense of inevitable, gravitational motion that pulls the listener through the progression. Classical composers discovered this centuries ago. The "lament bass" of Baroque music (a descending chromatic line from tonic to dominant) became one of the most powerful expressive devices in the repertoire. Purcell's "When I Am Laid in Earth" from Dido and Aeneas is the famous example - the bass descends chromatically while the harmony shifts above it, creating unbearable emotional weight from the simplest possible motion.
In jazz, chromatic bass lines appear everywhere from stride piano to modern big band writing. Thad Jones was a master of arranging inner voices to create chromatic motion beneath the surface of otherwise diatonic harmony. The technique gives any progression a sense of direction and sophistication.
The algorithm takes the first and last chord of a progression as fixed endpoints and rewrites the inner chords so that the bass moves by half steps between them. It calculates the chromatic distance between the two roots, checks whether the inner slots can accommodate the needed steps, and assigns new roots by semitone increments. For each new root, it selects a chord quality based on the diatonic degree in the current key - if the root falls on a natural diatonic degree, it gets the appropriate quality (ii gets m7, IV gets maj7, V gets 7). If the root falls on a chromatic degree, it defaults to a dominant seventh. The engine tries both ascending and descending directions and keeps whichever produces valid results.
Endpoints: Cmaj7 (C) → Fmaj7 (F)
Distance: 5 semitones ascending
Inner slots: 4
Result: Cmaj7 - Dbmaj7 - Dm7 - Ebmaj7 - Em7 - Fmaj7
Bass: C → Db → D → Eb → E → F (chromatic ascent)
Every bass note is one half step from the next.
The harmony above adapts. The bass line commands.12. Line Cliché (CESH)
The line cliché - also known as CESH (Chromatic Embellishment of Static Harmony) - is what happens when a single voice inside a chord moves chromatically while everything else stays put. You've heard it a thousand times. The James Bond theme. "My Funny Valentine." The verse of "Stairway to Heaven." Bossa nova intros. It's one of the most recognizable harmonic devices in popular music, and its power comes from the tension between stasis and motion - most of the chord is frozen while one voice slides.
The classic pattern on a minor chord descends from the root through the major seventh, the minor seventh, and the sixth: Am → Am(maj7) → Am7 → Am6. The moving voice (A → G# → G → F#) creates a chromatic descent within the chord while the other notes (A, C, E) remain static. Burt Bacharach loved this device. Antonio Carlos Jobim built entire songs around it. In jazz, it's a way to create harmonic motion without actually changing the chord - the key center stays planted, but the inner voice tells a story of gradual descent.
The algorithm recognizes four starting qualities and applies the appropriate pattern. Minor triads get the full four-chord descent (m → m(maj7) → m7 → m6). Minor sevenths continue the descent from their starting point (m7 → m6). Major sevenths descend through the dominant seventh to the sixth (maj7 → 7 → 6). Major triads get the full descent from the octave (root → maj7 → 7 → 6). The engine also detects consecutive chords with the same root and applies the pattern across them, creating the cliché without expanding the progression.
Minor triad line cliché:
Am → Am(maj7) → Am7 → Am6
Moving voice: A → G# → G → F#
Static voices: A, C, E (unchanged)
Major seventh line cliché:
Cmaj7 → C7 → C6
Moving voice: B → Bb → A
Static voices: C, E, G (unchanged)
The chord barely changes. One voice tells the whole story.13. Constant Structure
Constant structure is one of the most modern-sounding techniques in the engine, and its roots are in the modal jazz of the 1960s. The idea: take a progression and change every inner chord to the same quality while preserving the root motion. If the original progression is Cmaj7-Dm7-Em7-Fmaj7, a constant-structure reharmonization might make it Cmaj7-Dmaj7-Emaj7-Fmaj7 - all major sevenths, moving in parallel. The harmonic function dissolves, replaced by a floating, non-functional quality that sounds neither major nor minor but somewhere entirely else.
Bill Evans explored this idea on recordings like "Time Remembered," where chords of similar quality move through non-functional root motion, creating a dreamy, suspended atmosphere. Herbie Hancock took it further on "Maiden Voyage," where the entire composition is built from dominant seventh chords moving in fourths and half steps - no functional resolution anywhere, just a constant harmonic color drifting through different keys. Wayne Shorter's compositions for the Miles Davis Quintet ("Nefertiti," "Fall") use constant structures to create harmony that seems to float above traditional gravity.
The algorithm attempts four variants: all chords converted to maj7, all to m7, all to dominant 7, and all to m7b5 (half-diminished). The first and last chords stay as anchors. Only the inner chords are transformed. The result is four different parallel-motion reharmonizations, each with a distinct character - the all-maj7 version sounds luminous, the all-m7 version sounds introspective, the all-7 version sounds like Hancock, and the all-m7b5 version sounds like the harmony is dissolving.
Original: Cmaj7 - Dm7 - G7 - Cmaj7
All maj7: Cmaj7 - Dmaj7 - Gmaj7 - Cmaj7
All m7: Cmaj7 - Dm7 - Gm7 - Cmaj7
All dom7: Cmaj7 - D7 - G7 - Cmaj7 (Hancock)
All m7b5: Cmaj7 - Dm7b5 - Gm7b5 - Cmaj7 (dissolving)
Same roots. Same motion. Four different universes.14. Pedal Point
A pedal point is the oldest harmonic device on this list - older than jazz, older than classical harmony, older than notation itself. The concept: hold one bass note static while the chords above it move freely. The sustained bass creates a gravitational anchor, and as the upper harmony drifts away from it and returns, the listener experiences tension and release without any change in the bass. Organ music lives on pedal points. So does gospel. So does John Coltrane's "A Love Supreme," where the opening bass figure stays rooted while the saxophone soars through key after key above it.
There are two classic pedal types. A tonic pedal holds the root of the key in the bass, creating stability even when the upper chords move to distant harmonies. It's the sound of home, of certainty, of the ground beneath your feet remaining solid while the sky changes color. A dominant pedal holds the fifth of the key, creating sustained tension - a feeling of "almost there" that intensifies the eventual resolution to the tonic. Beethoven used dominant pedals at the end of development sections, sometimes sustaining the tension for pages before releasing into the recapitulation.
The algorithm produces two variants for any progression. The tonic pedal converts every non-tonic chord to a slash chord over the tonic root (Dm7/C, G7/C, Am7/C). The dominant pedal does the same over the fifth degree (Cmaj7/G, Dm7/G, Am7/G). Chords already on the pedal note are left unchanged - Cmaj7 doesn't become Cmaj7/C. The slash chord notation tells the performer exactly what's happening: play the upper chord voicing, but keep the bass on the pedal note. It's harmony in layers.
Original: Cmaj7 - Dm7 - G7 - Cmaj7 (key of C)
Tonic pedal (bass = C):
Cmaj7 - Dm7/C - G7/C - Cmaj7
Dominant pedal (bass = G):
Cmaj7/G - Dm7/G - G7 - Cmaj7/G
The chords move. The ground stays.
Tension builds through the contradiction.How They Work Together
No single technique defines a reharmonization. The power is in combination. Take a simple ii-V-I in C major: Dm7-G7-Cmaj7. Apply tritone substitution to the G7 and you get Dm7-Db7-Cmaj7. Now apply a passing diminished between Dm7 and Db7 (they're a half step apart, so it doesn't apply - but between Cmaj7 and Dm7 in the next chorus, it would). Layer a pedal point underneath and the bass stays on C while the tritone-substituted Db7 creates maximum harmonic friction above it. Each technique is a tool. The reharmonization is the craft of choosing which tools to use and where.
JMove's engine doesn't combine techniques automatically - that would be making creative decisions that belong to the musician. Instead, it presents each technique's results separately, ranked by voice-leading smoothness, with the original and reharmonized progressions shown side by side. Changed chords are highlighted so you can see exactly what moved. You click, you listen, you decide. The engine is the encyclopedia. You're the artist.
These fourteen techniques span four centuries of harmonic thinking - from Bach's borrowed chords to Coltrane's symmetrical divisions to Holdsworth's scale families. They represent different answers to the same question every musician eventually asks: what else could this harmony be? The question has no final answer. That's why it's worth asking.
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