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Jazz harmony is built on idiomatic progressions and substitutions that elaborate and extend the tonal system. The ii–V–I progression (e.g., Dm7–G7–Cmaj7) is the fundamental building block of jazz harmony, analogous to the ii–V–I authentic cadence in classical theory but extended with seventh chords throughout. The 12-bar blues form structures a complete harmonic cycle using dominant seventh chords on I, IV, and V. Tritone substitution replaces any dominant seventh chord with the dominant seventh chord a tritone away, exploiting their shared tritone to create chromatic bass motion. Chord extensions and alterations on dominant chords are stylistically expected rather than exceptional.
Learn the ii–V–I in all 12 keys, playing the progression with seventh chord voicings until it is automatic. Then learn the 12-bar blues form and improvise over it. Study jazz standards by analyzing their harmonic structure as a series of ii–V–I cycles moving through different key areas. Listen to bebop recordings (Charlie Parker, Dizzy Gillespie) to hear how the progressions are elaborated in real performance.
If you already know how ii–V–I functions in classical harmony, jazz harmony will feel like a natural extension rather than a foreign language. The ii–V–I is simply the ii–V–I authentic cadence you know from tonal harmony, but with seventh chords on every chord — Dm7–G7–Cmaj7 in the key of C. The G7 pulls to Cmaj7 for exactly the same reason it always does in tonal music: the leading tone (B) resolves up to C, and the chordal seventh (F) resolves down to E. Jazz adds the thirds, sevenths, ninths, and thirteenths, but the underlying tension-and-release logic is unchanged.
The 12-bar blues is a complete harmonic form built from dominant seventh chords, which is worth noting because it differs from classical practice. In classical music, dominant seventh chords are unstable and demand resolution. In the blues, I7, IV7, and V7 are all stable — the blues is a tonal system where dominant quality is the norm, not an exception. A basic 12-bar blues in C goes roughly: C7 (4 bars) | F7 (2 bars) | C7 (2 bars) | G7 (1 bar) | F7 (1 bar) | C7 (2 bars). Learning to hear and play this form fluently is essential because jazz standards frequently embed blues-derived harmonic cycles within their structures.
Tritone substitution is the most powerful single tool in jazz harmonic vocabulary. The rule is simple: any dominant seventh chord can be replaced by the dominant seventh chord a tritone away. G7 can become Db7. The reason this works is that G7 and Db7 share the same tritone internally — the two most harmonically tense notes of G7 are B and F, and Db7 also contains these pitches (spelled as Cb and F). Because the defining tension of a dominant chord lives in its tritone, two chords a tritone apart are essentially the same functional object. What the substitution adds is a chromatic bass line: instead of G resolving down a fifth to C, Db slides down a half-step to C — a much smoother motion.
Jazz harmonic language also normalizes chord extensions and alterations that classical harmony treats as dissonances. On a G7 in jazz, it is entirely normal — expected, even — to add a b9, #9, #11, or b13. These alterations increase tension and color without changing the chord's Dominant function. When analyzing jazz, do not assume that an altered chord is doing something unusual; in context, G7alt simply means "a very tense dominant heading to C, decorated with chromatic color tones."
The practical path into jazz harmony runs through repetition and ear training. Learn the ii–V–I in all 12 keys until the sound is automatic. Then study jazz standards — most of their chord changes are just ii–V–I cycles moving through different key areas, sometimes with tritone subs inserted. Listen to bebop recordings and try to identify the ii–V–I cycles by ear before checking the sheet music. Jazz harmony rewards this kind of active, listening-centered study more than passive reading ever will.
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