Changing the changes
How do you reharmonize a song on guitar?
You have learned to voice a chord richly — the seventh added, the doubled root dropped, a little color on top, the shapes connecting smoothly. All of that dresses the chords that are already there. Reharmonizing is the next thing: keeping the melody and changing the chords — the changes — underneath it, for ones that lean where the old ones just sat. It sounds like composition. On the guitar it is often a single finger.
The same tune, new chords
Reharmonization keeps one thing fixed — the melody — and swaps the harmony beneath it. Here is the pop turnaround you may already have voiced for jazz: Cmaj7, A minor 7, F major 7, G7, four chords straight out of the key of C. Then the same span of music, same melody on top, with three of those chords traded for richer ones. A bass plays each chord's root underneath, so you can hear the bottom of the harmony move — because that is where half of reharmonization happens.
The chords and bass you hear are the app’s own sampled instruments — from the MuseScore General sound library, used under the MIT license.
The melody never changed. Three of the four chords did, and the whole thing tilts from a folk turnaround toward a jazz one. Here is the map, and then the three moves that draw it — each one small, each one the same idea: replace a chord that sits with a chord that leans.
Move 1 — Make a chord lean
The workhorse of reharmonization is the secondary dominant. A plain chord sits; a dominant seventh chord leans, pulling hard toward the chord a fourth above it — that is what a G7 does to a C. The move is to hand that pull to a chord that did not have it. Take the A minor in the turnaround and make it A7. It now leans toward D, so give it somewhere to land: relax the F to D minor 7. The back half of your pop progression is suddenly a ii–V — Dm7 to G7 — the two chords under a thousand standards.
On the guitar the whole move is one note. A minor 7 and A7 are the same grip with a single string a fret apart: the minor third becomes a major third, and a resting chord starts to pull.
Root, flat third, fifth, flat seventh — a settled minor chord, in no hurry to be anywhere.
One string up a fret — C to C♯, the major third — and the chord tips forward, pulling toward the D minor that follows.
That single move — one chord made dominant, one chord relaxed to catch it — is most of the distance. The ii–V it uncovers is the same pair you aim solos at, so the notes to land on are the guide tones you already know. Any diatonic chord can take this treatment: a D7 to lean into the G, an E7 to lean into the A minor. Each one is a plain chord with its third pushed up to a leading tone.
Move 2 — Give the dominant its own two-five
The second move is the first one again, layered. A dominant sounds even more inevitable when its own ii comes first — the same ii–V relationship, one level down. Put an E minor 7 in front of the A7, and Em7 A7 is a ii–V pointing at D minor, just as Dm7 G7 points at C. String them together and the turnaround becomes a chain of two-fives walking home — which is to say, it fills with the exact grips the drop-2 vocabulary is built from.
This move adds a chord rather than changing one, so it needs a little room — a bar you can split in two, or a slower spot in the tune. But it is free theory: no new shapes, no new idea, just the ii–V you already trust, planted in front of each dominant that will hold still long enough to hear it.
Move 3 — Trade a dominant for its twin
The move that sounds the most like jazz for the least effort is the tritone substitution. Two dominant sevenths whose roots are a tritone apart — G7 and D♭7 — share the same two guide tones: the notes B and F that give a G7 its pull are, in a D♭7, its seventh and third, the same tension spelled the other way round. So D♭7 can stand in for G7 with the same pull home. What changes is the root: D♭ sits a half step above the C you are landing on, so the bass slides down chromatically — D, D♭, C — and that descent is the sound.
On the guitar the shared tritone means the two lowest strings of the grip do not move at all. Only the top two shift, a fret each.
The F on the D string and the B on the G string are the tritone — the engine of the chord.
The F and B stay put — now the third and seventh of D♭7. The same tritone that made a G7 makes its twin.
Only the last chord changed, and the bottom of the harmony now walks down by half steps into the C. That chromatic bass is the tell of a hundred jazz endings, and you bought it with two fingers.
The gentle one: swap for a relative
Not every move needs a dominant. The quietest reharmonization is diatonic substitution — trading a chord for another already in the key that shares most of its notes. C major 7, E minor 7, and A minor 7 all live within a whisker of one another; so do F major 7 and D minor 7. Put a chord from that family where the melody note still fits and the color shifts without the ground moving under it — an easy way to keep a repeated phrase from landing on the same chord twice. It changes the shade; the dominants change the pull.
How far to take it
There is no ceiling on this, which is exactly the trap. You can lean every chord, give each its own ii–V, tritone-sub half of them, and end up with a progression so busy the tune drowns. Two rules keep it musical. First, the melody stays the boss: a substitute chord has to contain, or comfortably sit under, the note being sung — reharmonization serves the melody, it does not outvote it. Second, the swaps only sound composed if the voices move smoothly from one chord to the next; a clever substitution grabbed in a distant shape sounds like a mistake, while the same chord voiced a fret away sounds inevitable. Change the chords, then connect them — that second half is where the polish lives.
Where Drop2 comes in
Every chord above is a four-note voicing — the third and seventh and two chosen notes, on the top strings. That vocabulary is what the Drop2 app drills. Learn and Train cover every inversion of maj7, 7, m7, m7♭5, dim7, and mMaj7 across all three string sets, free with no time limit, and the app listens through your phone’s microphone and grades each grip by ear — so the A7 or the D♭7 you reach for is the one you meant. The app will not pick your substitutions; that is your ear and your taste. What it gives you is the shapes, cold, so that when you decide to reharmonize a tune the chords are already under your fingers.
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