Chord-Scale Theory is an approach to improvising that relates chords to scales.

The name "Chord-Scale Theory" comes from the idea that the notes of a thirteenth chord can be rearranged as a seven-note scale.

To determine chord-scales, identify key centers and chord functions through Roman numeral analysis.

Roman numerals can be related to mode numbers. For example, if a chord is a ii chord in a major key, the second mode (dorian) can be used to color that chord.

When playing chord-scales, place chord tones on the downbeat to connect improvised melodies to the chord progression.

This book covers modes from many different angles. For more information on modes, check Introduction to Diatonic Modes (general), Modal Schemas (pop), Diatonic Modes (20th/21st-c.), and Analyzing with Modes, Scales, and Collections (20th-/21st-c.).

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One of the challenges of improvising jazz is making choices about pitches while also paying attention to groove, interaction, and narrative form. The Chord-Scale Theory is a method, taught at the Berklee College of Music and many other colleges and universities, that facilitates pitch choices in jazz improvisation. Chord-Scale Theory is based on George Russell’s Lydian Chromatic Concept of Tonal Organization ([1953] 2001), and it was popularized by jazz educators Jamey Aebersold, David Baker, and Jerry Coker.

The basic concept is that every chord comes from a parent scale; or, to put it another way, every chord in a progression can be colored by a related scale. For example, a Dmi7 chord extended to the thirteenth consists of the notes D, F, A, C, E, G, and B, which are identical to the notes of the D dorian mode stacked in thirds (Example 1). Therefore, when confronting a Dmi7 chord in a chord progression, an improvising musician could choose to improvise using the notes of the D dorian mode to create new melodies.

Example 1. A Dmi13 chord and a D dorian scale have identical pitches.

Basic Chord-Scale Relationships

Starting a major scale on each of its seven notes will yield seven different modes. Each of the modes will have a different pattern of half steps and whole steps and thus a different color. (For more information, see Introduction to Diatonic Modes and/or Diatonic Modes).

Since the ii–V–I schema is so common in jazz standards, the three chord-scale relationships in Example 2 are often taught first. Example 3 shows these three relationships within the context of a ii–V–I progression in C.

Example 2. Basic chord-scale relationships.

Example 3. Chord-scale relationships in a ii–V–I progression in C.

A beginning improviser might approach a song consisting mainly of ii–V–I progressions by simply applying the dorian mode to minor seventh chords, the mixolydian mode to dominant seventh chords, and the ionian mode to major seventh chords. As Example 4 shows, an improvised melody can imply a harmony by placing chord tones on the downbeats, and a seven-note mode can be thought of as a four-note seventh chord with three passing tones (\hat{2}, \hat{4}, \hat{6}) or extensions (ninth, eleventh, thirteenth).

Example 4. The basic chord-scale relationships for ii–V–I as they might be used in "Tune Up" by Miles Davis (1953).

Chord-Scales and Major Keys

There are many more possible chord-scale relationships beyond those above. The seven notes of the diatonic scale suggest seven basic chord-scale relationships, as summarized in Examples 5 and 6.

Example 5. Chord-scale relationships between Roman numerals and modes.

Example 6. Chord-scale relationships for all diatonic harmonies in C.

A similar approach to the one above can be used to derive more chord-scale relationships from the melodic minor, harmonic minor, and harmonic major modes. To learn more about this, consult Further Reading below.

Applying Chord-Scales to Progressions within a Key

Reorganizing these relationships by chord quality reveals the choices listed in Example 7 for matching chord qualities to scales. For example, when improvising on a minor seventh chord, a musician can choose from three chord-scales: dorian, phrygian, or aeolian (Example 8).

Example 7. The same chord-scale relationships as in Example 5, rearranged by chord quality.

Example 8. Chord-scale choices for a minor-seventh chord.

However, it's important to realize that Chord-Scale Theory does not imply that the key modulates each time the chord changes. In other words, these chord-scales are not key centers. Since each mode will imply different extensions, identifying chord functions through Roman numeral analysis helps an improviser choose chord-scales that best fit the key center.

For example, the opening measures of “Fly Me to the Moon” (1954) contain six of the seven diatonic chord-scale relationships in a circle-of-fifths root movement (Example 9). The chord progression in this example is clearly in the key of C, not seven different keys. Rather than simply coloring each minor chord with a dorian mode and each major chord with an ionian mode, differentiating between the vi and ii chords and between the I and IV chords will result in a more natural-sounding improvised line.

Example 9. These chord-scales applied to ["Fl