# AI Wiki - Music - Reharmonization ## Overview Reharmonization means keeping a melody and changing the chords under it. The tune stays recognisable, but its mood, colour and sense of motion change: a nursery rhyme can sound like a hymn, a [[AI Wiki - Music - Pop Music|pop]] ballad or a jazz standard depending on the chords you choose. Wikipedia describes the core idea neatly: one melody note can act as the root, third, ninth or ♯5 of different chords, so every note offers several harmonic choices. Reharmonization builds directly on [[AI Wiki - Music - Diatonic Chords and Roman Numerals]] (which chords belong to a key and what they do) and [[AI Wiki - Music - Common Chord Progressions]] (the defaults you're replacing). It's also the main tool of [[AI Wiki - Music - Arranging Songs]] and a rich source of ideas for [[AI Wiki - Music - Songwriting]]. In [[AI Wiki - Music - Jazz Music]], musicians reharmonize standards all the time. ## The one rule: respect the melody note Any new chord must fit the melody note that sounds over it. Three outcomes: - **The melody is a [[AI Wiki - Music - Chord Tones and Improvisation|chord tone]]** (root, 3rd, 5th or 7th): always safe. - **The melody is a colour tone** (a 9th, a 6th, an 11th over a minor chord): fine, often lovely. - **The melody sits a half step above a chord tone** (the 4th over a major chord, a ♭9 over anything but a dominant): a clash. Passing quickly, it's tolerable; held on a long note, it sounds wrong. So before swapping a chord, name the melody notes it has to carry, especially the long notes and the notes on beat 1. On guitar, sing or hum the melody while [[AI Wiki - Music - Strumming Patterns|strumming]] the candidate chord: your ear catches clashes faster than theory does. ## Technique 1: diatonic substitution Chords a third apart share two of their three notes, so they can stand in for each other. In C, C (C E G), Am (A C E) and Em (E G B) all share notes and all have a tonic function. In practice: | Original | Substitute | Shared notes | Effect | |---|---|---|---| | I (C) | vi (Am) | C, E | darker, the [[AI Wiki - Music - Relative and Parallel Keys\|relative minor]] | | I (C) | iii (Em) | E, G | softer, unresolved | | IV (F) | ii (Dm) | F, A | gentler, sets up V better | | V (G) | vii° (Bdim) or V7 | B, D | more tension | The ii-for-IV swap is the most useful one: Dm leads to G more smoothly than F does, which is why ii–V–I is the jazz version of IV–V–I. ```keyboard range: C4-B4 --- title: C (I) chord: C --- title: Am (vi): shares C and E chord: Am --- title: Em (iii): shares E and G chord: Em ``` ## Technique 2: secondary dominants Any major or minor chord in the key can be preceded by its own dominant seventh, borrowed for a moment: V7 of that chord, written V7/x. In C major: | Secondary dominant | Resolves to | Sounds like | |---|---|---| | D7 (V7/V) | G | "Don't Think Twice, It's All Right" (Dylan) uses this II7 | | E7 (V7/vi) | Am | "The Shoop Shoop Song" uses this III7 | | A7 (V7/ii) | Dm | the classic turn into ii | | C7 (V7/IV) | F | the "going to IV" pull of gospel and blues | | B7 (V7/iii) | Em | rarer, more dramatic | The diminished vii° isn't tonicized, and the tonic doesn't need one (V7 already is its dominant). Each secondary dominant brings one note from outside the key, the raised third that acts as a temporary leading tone (C♯ in A7, F♯ in D7, G♯ in E7), which is where the extra pull comes from. Chains are possible too: A7 → D7 → G7 → C, each resolving down a fifth, opens "Sweet Georgia Brown" and the ragtime progression. See [[AI Wiki - Music - Seventh Chords]] and [[AI Wiki - Music - Circle of Fifths]]. The good news for open-chord players: in C and G, almost all secondary dominants are open shapes. ```chord C7 x32310 x32410 --- A7 x02020 x02030 --- D7 xx0212 xx0213 --- E7 020100 020100 --- G7 320001 320001 ``` Watch the melody: E7 contains G♯, so it clashes with a melody G. That's the most common way a secondary dominant fails. ## Technique 3: borrowed chords Borrowing a chord from the parallel minor (modal interchange) tints a major-key song without leaving the key. The favourites in a major key are iv, ♭VI, ♭VII and ♭III; [[AI Wiki - Music - Relative and Parallel Keys]] covers them with song examples. As a reharmonization move: - **IV → iv**: replace the second half of a IV bar with iv (C → Cm in G). The wistful, Beatles-ballad sound. The melody must avoid the major third of IV (B over Cm in G) at that moment. - **V → ♭VII**: end a phrase ♭VII–I instead of V–I (F → G in G). A [[AI Wiki - Music - Rock Music|rock]] and anthemic cadence; see [[AI Wiki - Music - Cadences]]. - **IV → ♭VI**: a cinematic lift (E♭ in G). ## Technique 4: tritone substitution A dominant seventh can be replaced by the dominant seventh a tritone (three whole tones) away: D♭7 for G7 in C. It works because both chords share the same tritone between their third and seventh, with the roles swapped. G7's third is B and its seventh is F; D♭7's third is F and its seventh is C♭, which is B. Those two notes are what pull to C, so both chords resolve the same way. ```keyboard range: C4-B5 labels: intervals --- title: G7: tritone B-F chord: G7 highlight: 3 b7 --- title: Db7: same tritone, swapped chord: Db7 highlight: 3 b7 ``` The payoff is in the bass: Dm7–G7–C (roots falling a fifth) becomes Dm7–D♭7–C, a chromatic slide D–D♭–C. Every secondary dominant can be tritone-substituted the same way: A7 → Dm can become E♭7 → Dm. In a 12-bar [[AI Wiki - Music - Blues Music|blues]] in C, swapping bar 4's C7 for G♭7 is one of the most common uses. The device belongs mostly to [[AI Wiki - Music - Jazz Music]]; in folk or country it sounds out of place. On guitar, the tritone subs are movable shapes: ```chord Eb7 xx1323 xx1324 --- Db7 x46464 x13141 --- Ab7 464544 131211 ``` The tritone sub has strict melody limits: D♭7 puts D♭ and A♭ against the melody. Over a melody D, it sounds as a harsh ♭9. Over a melody F or B, it's perfect. ## Technique 5: passing and approach chords Instead of replacing a chord, insert one between two chords to smooth the bass line: - **Diminished passing chord**: I – ♯I°7 – ii (G – G♯°7 – Am in G). The bass rises by half step and the diminished chord acts like a rootless V7/ii. - **Slash-chord bass lines**: C – C/B – Am – Am/G – F (a falling bass under one chord shape; see [[AI Wiki - Music - Piano Chord Inversions]]). - **Chromatic approach**: slide into the target chord from a fret above or below on the beat before (E♭7 → D7 → G). - **Adding ii before V**: turn any V into ii–V (G – Am7 D7 – G instead of G – D – G). The simplest jazz upgrade of all. ```chord G 320003 210003 --- G#dim7 xx3434 xx1324 --- Am7 x02010 x02010 --- D7 xx0212 xx0213 ``` ## A worked example: "Twinkle Twinkle Little Star" The traditional melody in C (C C G G | A A G | F F E E | D D C) is the cleanest test bed: you know it by heart, so you hear every new chord. Each version below keeps every melody note a chord tone or a mild colour tone. The original harmony, I, IV and V only: ```chords {title: Twinkle Twinkle: original} {key: C} {time: 4/4} [C]Twinkle twinkle [F]little [C]star, [F]how I [C]wonder [G]what you [C]are ``` Diatonic substitution: Em and C/E take turns on the I, Dm replaces F, Am stands in for C, and the bass walks C–E–F–E–D–A–G–C. ```chords {title: Twinkle Twinkle: diatonic substitutes} {key: C} {time: 4/4} [C]Twinkle [Em]twinkle [F]little [C/E]star, [Dm]how I [Am]wonder [G7]what you [C]are ``` Secondary dominants: C7 points to F, A7 to Dm, D7 to G7. The melody G sits on C7 as its 5th and on A7 as its ♭7; the melody D is the root of D7. ```chords {title: Twinkle Twinkle: secondary dominants} {key: C} {time: 4/4} [C]Twinkle [C7]twinkle [F]little [A7]star, [Dm]how I [Am]wonder [D7]what [G7]you [C]are ``` Jazz version: sixth and seventh chords (C6 rather than Cmaj7 under a melody C, whose B would rub against it) and a tritone sub (E♭7 replaces A7 on "star"; the melody G is its third, and the bass falls E♭–D into Dm7). ```chords {title: Twinkle Twinkle: jazz} {key: C} {time: 4/4} [C6]Twinkle [Em7]twinkle [Fmaj7]little [Eb7]star, [Dm7]how I [Am7]wonder [Dm7]what [G7]you [C6]are ``` Play the four versions back to back. The tune doesn't change; the story does. ## Applying it to a simple song For a three- or four-chord song in G (G, C, D, Em), work in this order, one change at a time: 1. **Change the harmonic rhythm**: add a chord on beat 3 where a chord lasts two bars, or hold one chord longer. 2. **Diatonic swaps**: Em for G, Am for C. 3. **One secondary dominant**: E7 before Am, or B7 before Em. 4. **One borrowed chord**: C → Cm before returning to G. 5. **Only then**, if the style allows, ii–V insertions and tritone subs. ```chords {title: One loop, four ways} {key: G} {time: 4/4} {start_of_verse: Original} [G]1 2 3 4 [G]1 2 3 4 [C]1 2 3 4 [D]1 2 3 4 {end_of_verse} {start_of_verse: Diatonic} [G]1 2 3 4 [Em]1 2 3 4 [C]1 2 3 4 [D]1 2 3 4 {end_of_verse} {start_of_verse: Secondary dominant} [G]1 2 3 4 [E7]1 2 3 4 [Am]1 2 3 4 [D7]1 2 3 4 {end_of_verse} {start_of_verse: Borrowed iv} [G]1 2 3 4 [Em]1 2 3 4 [C]1 2 [Cm]3 4 [D]1 2 3 4 {end_of_verse} ``` Use the reharmonized loop for one section only (a last chorus, an outro or a solo intro). That's how arrangers use it: contrast, not a total rewrite. ## On piano Piano makes reharmonization easy to hear because every voice is visible. Keep the melody on top in the right hand, play the new chord below it, and move the inner voices as little as possible ([[AI Wiki - Music - Piano Voicings]]). Left-hand roots make the new bass line obvious, which is often the real point of a reharmonization. ## How to practise - **Harmonize one melody five ways.** "Twinkle", "Happy Birthday" or "Amazing Grace": find every chord that contains each long note. - **Ear first**: play each version and name what changed by ear ([[AI Wiki - Music - Chord Progression Recognition]]). - **Transcribe reharms**: compare a cover with the original and list the substitutions ([[AI Wiki - Music - Transcription and Playing by Ear]]). - **Log new chords as items**: each new shape (E♭7, G♯°7) is a chord note to learn, then a chord change drill (A7 → Dm, E♭7 → Dm). ## Common mistakes - **Ignoring the melody**: the new chord sounds great alone and terrible under the tune. - **Reharmonizing everything**: one or two changes per section are more effective than ten. - **Style mismatch**: tritone subs in a campfire song, borrowed ♭VI in a blues [[AI Wiki - Music - Swing and Shuffle Feel|shuffle]]. - **Forgetting the bass**: a substitute with a clumsy bass line loses its purpose; inversions often fix it. - **Not telling the band**: a reharmonized chart must be written down for others ([[AI Wiki - Music - Playing with Others and Jamming]]). ## Key Points - Reharmonization keeps the melody and changes the chords; the melody note must be a chord tone or a good colour tone. - Diatonic substitution: chords a third apart share two notes (vi or iii for I, ii for IV). - Secondary dominants (V7/x) borrow a temporary leading tone; in C and G most are open shapes. - Borrowed chords (iv, ♭VI, ♭VII, ♭III) add minor colour without leaving the key. - Tritone substitution swaps V7 for the dominant a tritone away (D♭7 for G7): same 3rd–7th tritone, chromatic bass. - Passing chords (♯I°7, slash-chord bass lines, inserted ii–V) smooth the motion between existing chords. - Change one thing at a time, and use reharmonization for contrast in one section. ## Open Questions - **Answered** ([[AI Wiki - Music - Borrowed Chords and Modal Interchange|Borrowed Chords and Modal Interchange]]): Which reharmonization moves suit [[AI Wiki - Music - Folk Music]] and [[AI Wiki - Music - Country Music]] without sounding jazzy? IV–iv, ♭VII–I, ♭VI–♭VII–I, plain secondary dominants (II7, III7, ragtime VI7–II7–V7), I7–IV and walking slash-chord bass lines, keeping triads and sevenths rather than extensions and tritone subs. - How far can a reharmonization go before a song stops being recognisable to listeners? - Coltrane changes and multi-tonic systems: worth studying at this stage, or much later? ## References - Wikipedia: Reharmonization. https://en.wikipedia.org/wiki/Reharmonization - Wikipedia: Chord substitution. https://en.wikipedia.org/wiki/Chord_substitution - Wikipedia: Secondary chord. https://en.wikipedia.org/wiki/Secondary_chord - Wikipedia: Tritone substitution. https://en.wikipedia.org/wiki/Tritone_substitution - Wikipedia: Borrowed chord. https://en.wikipedia.org/wiki/Borrowed_chord - Hub Guitar: Substitute dominant or "tritone sub" chords. https://hubguitar.com/music-theory/tritone-substitute-dominant-chords ## Related - [[AI Wiki - Music - Diatonic Chords and Roman Numerals]] - [[AI Wiki - Music - Common Chord Progressions]] - [[AI Wiki - Music - Seventh Chords]] - [[AI Wiki - Music - Relative and Parallel Keys]] - [[AI Wiki - Music - Circle of Fifths]] - [[AI Wiki - Music - Cadences]] - [[AI Wiki - Music - Piano Voicings]] - [[AI Wiki - Music - Piano Chord Inversions]] - [[AI Wiki - Music - Jazz Music]] - [[AI Wiki - Music - Arranging Songs]] - [[AI Wiki - Music - Songwriting]] - [[AI Wiki - Music - Playing with Others and Jamming]] - [[AI Wiki - Music - Chord Progression Recognition]] - [[AI Wiki - Music - Transcription and Playing by Ear]] - [[AI Wiki - Music - Fingerstyle Arranging]] - [[AI Wiki - Music - Keys and Key Signatures]] - [[AI Wiki - Music - Playing from Lead Sheets]]