Tonal harmony extends far beyond the seven diatonic chords. Chromatic chords — borrowed from other keys, altered, or extended — create the color and intensity that distinguishes advanced tonal writing from basic four-part chorale.
BEYOND THE DIATONIC
Once the seven diatonic chords are mastered, the chromatic extensions of tonal harmony open a vast new territory. These extensions do not abandon the tonal system — they enrich it, creating more complex paths through harmonic space and more varied emotional colors.
SECONDARY DOMINANTS
Every chord in the key can be preceded by its own dominant — a chord borrowed from the temporary "key" of that target chord. This is called a secondary dominant or applied dominant.
Example in C major: the chord D–F#–A (a major triad) is not diatonic to C major, but it functions as V of V — the dominant of the G major chord (ii → V of V → V → I). The F# creates a momentary lean toward G before returning to C.
Secondary dominants appear throughout the Classical and Romantic repertoire. Mozart uses them freely in his piano sonatas; Schubert's songs are full of them; they are the primary harmonic device in jazz standards.
BORROWED CHORDS (MODAL MIXTURE)
Chords can be borrowed from the parallel minor key. In C major, borrowing from C minor gives access to bIII (E♭ major), bVI (A♭ major), bVII (B♭ major), and the minor iv (F minor) — all adding a darker, more complex color to major-key writing.
The bVI is particularly expressive — its sudden appearance in a major key creates an effect of emotional shift, even tenderness, that composers from Schubert to the Beatles exploited constantly. The opening of Schubert's "Unfinished" Symphony uses it structurally.
AUGMENTED SIXTH CHORDS
The augmented sixth chord (Italian sixth, French sixth, German sixth) is a chromatic chord that intensifies the approach to the dominant. All forms contain the interval of an augmented sixth between the bass and an upper voice, creating a strong expansive pull toward the dominant.
The German augmented sixth chord sounds identical to a dominant seventh chord but functions differently — it resolves outward to V rather than inward to I.
NEAPOLITAN CHORD
The Neapolitan (♭II or N) is a major chord built on the lowered second scale degree. In C major: D♭–F–A♭. It appears typically in first inversion (♭II6) and progresses to V. Its sound is distinctive — wide, slightly ominous — and is strongly associated with dramatic or tragic contexts.
Schubert, Chopin, and Beethoven all use the Neapolitan extensively. It is one of the characteristic harmonies of the minor-key dramatic tradition.
EXTENDED CHORDS: SEVENTH, NINTH, ELEVENTH, THIRTEENTH
Adding a seventh to a triad creates a seventh chord (four notes). Adding further thirds creates ninth chords (five notes), eleventh chords (six notes), and thirteenth chords (seven notes — all seven scale degrees stacked in thirds).
In tonal music, extended chords are most common on the dominant. The dominant thirteenth chord (in jazz: G13 in C major) contains almost all the available pitches of the scale and resolves to I with a sense of maximum accumulation.
Jazz harmony makes systematic use of extended chords in ways that go beyond Classical tonal practice. Jazz notation (chord symbols: Dm7, G9, Cmaj7) expresses chord quality and extension efficiently. Bill Evans's use of 9th and 11th chords on tonic harmonies creates ambiguity about whether the chord is really "home" — a productive harmonic complexity.
CHROMATIC VOICE LEADING
The most powerful harmonic effects come not from isolated chromatic chords but from chromatic voice leading — step motion (including chromatic steps) in multiple voices simultaneously. When three or four voices each move by semitone in different directions, the result can create a transformation of harmonic color that no simple chord change achieves.
Wagner's Tristan chord (the first chord of the Prelude to Tristan und Isolde, composed 1857-59, premiered 1865) is the most discussed example: F–B–D#–G# resolves to a dominant seventh (E–G#–B–D), but the exact harmonic identity of the opening chord has been debated for 160 years. Its power comes from chromatic voice leading, not from any particular chord quality.
COMMON-TONE DIMINISHED SEVENTH CHORDS
Among the most colorful chromatic chords is the common-tone diminished seventh — a fully diminished seventh chord built on a non-diatonic root that shares a common tone with the chord it embellishes. In C major, the common-tone diminished seventh D#°7 (D#–F#–A–C) shares the note C with the C major chord it embellishes and resolves to it by chromatic step motion in adjacent voices. These chords appear constantly in late nineteenth-century music as expressive embellishments that intensify the approach to a target chord.
The diminished seventh chord's special property is its symmetrical construction — entirely of minor thirds — which means any of its four notes can be reinterpreted as the root. This makes diminished seventh chords pivot chords par excellence: any diminished seventh can lead to four different dominant seventh chords and therefore eight different keys. Romantic composers such as Chopin and Liszt use this flexibility constantly, reinterpreting a single diminished seventh chord to traverse remote tonal regions.
ENHARMONIC MODULATION
Enharmonic modulation reinterprets a chord as belonging to a different key by respelling its pitches. A German augmented sixth (A♭–C–E♭–F# in C major, resolving to V) sounds identical to an A♭ dominant seventh (A♭–C–E♭–G♭, where G♭ is enharmonically the same as F#) — which would resolve to D♭ major. By writing one and treating it as the other, a composer can pivot to a distantly related key with maximum surprise.
Schubert is the master of enharmonic modulation. His "Wanderer" Fantasy (D. 760) moves through C major, C# minor, E major, and A♭ major in sequence — keys that have no direct functional relationship in conventional theory but that Schubert connects through enharmonic and chromatic mediant relationships. The result feels both spontaneous and inevitable, an effect that more conventionally structured music cannot achieve.
CHROMATIC MEDIANT RELATIONSHIPS
A chromatic mediant relationship moves between two major chords (or two minor chords) whose roots are a third apart. C major to E major (up a major third), C major to A♭ major (down a major third), C major to E♭ major (up a minor third), C major to A major (down a minor third) — all create characteristic dramatic color that no diatonic progression provides.
These relationships became central to Romantic harmonic vocabulary. Schubert's "Unfinished" Symphony (B minor, 1822) places its second theme in G major, a third below, as a structural relationship. Bruckner builds entire symphonic landscapes from chromatic mediant motion. The film composer John Williams uses chromatic mediant relationships to signal majesty and grandeur in scores like Star Wars and Superman.
WAGNER, LISZT, AND THE DISSOLUTION OF FUNCTIONAL HARMONY
By the second half of the nineteenth century, chromatic harmony had become so pervasive that the basic tonal hierarchy began to dissolve. Wagner's Tristan und Isolde (1859) uses chromatic voice leading and unresolved dominant sevenths to suspend functional resolution for hours at a stretch. Liszt's late piano pieces (Nuages gris, 1881; La lugubre gondola, 1882) anticipate twentieth-century atonality by abandoning clear tonal centers in favor of slowly drifting harmonic clouds.
This was not a rejection of harmony but its extension to a point of crisis. The "Tristan chord" can be analyzed in many ways — none entirely satisfactory — because Wagner's harmonic procedure has moved beyond the framework that the analytical tools were built to describe. The history of twentieth-century music can be understood in part as the response to this crisis: Schoenberg's abandonment of tonality, Stravinsky's neoclassical reinvention of older harmonic systems, Debussy's exploration of non-functional modal harmony.
JAZZ HARMONY AND TONAL EXTENSIONS
Jazz harmony took the chromatic extensions of late Romantic music and systematized them. Every chord type in jazz has standard available extensions: a Cmaj7 chord can take added 9, 11 (avoid), 13, or #11. A Dm7 chord can take 9, 11, 13. A G7 chord can take 9, 11 (avoid in conventional use), 13, ♭9, #9, #11, ♭13. These extensions are not exotic — they are the basic vocabulary that working jazz musicians use constantly.
The tritone substitution — replacing a dominant seventh chord with a dominant seventh built a tritone away — is the characteristic jazz chromatic device. G7 (resolving to Cmaj7) can be replaced with D♭7 (which shares G7's tritone of B/F, reinterpreted as the C♭/F of D♭7). The result is a chromatic bass motion (D♭ → C) where the original would have had a fifth motion (G → C). Tritone substitution appears constantly in bebop and post-bop jazz harmonic vocabulary.
EXERCISE: CHROMATIC HARMONIZATION
Take a simple eight-bar melody and harmonize it twice: 1. Using only diatonic chords (I, ii, iii, IV, V, vi, vii°) 2. Adding secondary dominants, borrowed chords, or chromatic passing chords at at least three points
Sing or play both versions. What does the chromatic version add? What does it cost (in terms of simplicity or singability)? Then attempt a third version that introduces a single moment of chromatic mediant relationship — a sudden move to a major chord a third away from the established key, lasting perhaps two bars before returning. This single chromatic event is often more affecting than three minor chromatic alterations. Restraint in chromatic harmony, paradoxically, makes chromatic harmony more powerful.