The idea
The same melody can carry many harmonies. Reharmonizing means choosing different chords that still fit it, to give it another colour: jazzier, more emotional or more surprising. Arrangers do it all the time in covers, film scores and choir arrangements.
1. Diatonic substitution
Replace a chord with another chord in the same key that shares two of its three notes. In C major: C ↔ Am ↔ Em (rest) and F ↔ Dm (preparation). It's the safest change.
2. Secondary dominants
Before any chord you can place its dominant: the major chord with a seventh a fifth above. Before Am, E7; before Dm, A7. It creates a little tension that resolves on arrival.
3. ii–V
A dominant can be prepared by its own ii: before C, Dm7 – G7; before F, Gm7 – C7. Chaining ii–Vs is the backbone of jazz.
4. Tritone substitution
A dominant can be swapped for the one a tritone away: D♭7 instead of G7. They share the two notes that create the tension (B and F) and the bass slides down by semitones to C: D – D♭ – C.
5. Modal interchange
Borrow chords from the minor mode: in C major, Fm (very emotional before returning to C), B♭ or A♭. A classic pop and rock device.
6. Passing diminished chords
When the bass rises a tone between two chords, a diminished chord in between makes it climb by semitones: C – C♯dim7 – Dm.
7. Inversions and bass lines
Without changing the chords, putting another note in the bass creates a walking line: C – G/B – Am – Am/G – F.
The golden rule: the melody
The new chord has to get along with the melody note, especially on long notes and strong beats. Always test by singing over it.
Try it on your song
The tool on this page applies these techniques in the style you choose and explains every change. Then you can fine-tune it chord by chord.
Frequently asked questions
Is reharmonizing the same as transposing?
No. Transposing moves every chord up or down by the same amount; reharmonizing changes which chords are played.
Which technique is easiest to start with?
Sevenths and diatonic substitution. Then secondary dominants.