Edge Types

The 36-node graph connects every chord to its neighbours via 11 edge types, ordered roughly from consonant to dissonant. Each type is colour-coded on the Circle of Fifths, running green → red along that spectrum.

Fifth

C → G, G → D, D → A, …

Movement by a perfect fifth — the purest harmonic relationship after the octave. The circle of fifths is this relationship; every adjacent pair of major chords on the outer ring is a fifth apart. Extremely common in all styles.

Plagal

F → C, Bb → F, …

The reverse fifth — moving down a fifth (or up a fourth). The “Amen” cadence. Softer than a dominant resolution; it arrives home without the tension of a leading tone.

Diatonic

C → Dm, Dm → Em, Em → F, …

Movement between chords that are both native to the same major key — stepwise through the scale. The backbone of most pop and classical harmony.

Relative

C → Am, F → Dm, G → Em, …

A major chord moving to its relative minor (or vice versa). They share two of three notes, making the transition extremely smooth. Very common in pop.

ii–V–I

Dm → G → C, Am → D → G, …

The defining cadence of jazz. The ii chord (supertonic minor) resolves to the V (dominant), which resolves to the I (tonic). Each leg is a fifth apart, giving two consecutive fifth moves with extra tension from the dominant seventh.

Borrowed

C → Bb, C → Ab, C → Gm, …

Chords borrowed from the parallel minor (or other modes) into a major context. bVII (Bb in C major), bVI (Ab), bIII (Eb), and iv (Fm) are the most common. Gives a darker, more ambiguous colour without fully leaving the key.

Parallel

C → Cm, G → Gm, Am → A, …

Same root, swapped quality — major to minor or minor to major. Dramatic and immediate; the root stays fixed while the third shifts a semitone.

Dom7

G7 → C, D7 → G, …

A dominant seventh chord resolving to its tonic. The tritone between the third and seventh of the dom7 pulls hard toward resolution. The most conclusive cadence in tonal music.

Leading tone

Bdim → C, F#dim → G, …

A diminished chord resolving up a semitone to the tonic. The leading tone (seventh scale degree) is a half-step below the root; the diminished chord containing it creates maximum tension before release.

Chromatic mediant

C → E, C → Eb, C → A, C → Ab, …

Two chords of the same quality (both major or both minor) whose roots are a third apart. No smooth voice-leading, but a striking colour shift — common in film scores and neo-soul. C → E is a “bright” mediant; C → Ab is “dark.”

Tritone substitution

Db → C, Ab → G, …

A dominant chord substituted by the dominant a tritone away. Db7 and G7 share the same tritone (F–B / Cb–F), so Db7 resolves to C just as smoothly as G7 does. Essential in jazz reharmonisation; gives a chromatic, descending bass line.