Extensions & Avoid Notes
   

Compatibility

The heart of jazz theory is chord-scale compatibility, which allows multiple players to improvise heavily scale-based solo parts over chord changes. Chords are grouped into modes with which they are said to be compatible.

This is not a hard-fast rule, just a way to remember which chords are connected to the their scalar counterparts. In other words, an experienced jazz musician can look at a series of chords and know which scales (and which notes of those scales) will sound good over the chord changes, and can figure out how to harmonize a melody by looking at the notes of the melody (horizontal axis) and determining which chord changes fit underneath (vertical axis).

Extensions

For each mode, chords can be built from the root, third, fifth, and seventh scale degrees. The ninth, eleventh, and thirteenth scale degrees may be available as extensions, tensions or alterations, if they are not intolerably dissonant avoid notes (more below).

Tap to hear the C Major scale played sequentially, (left) followed by the C Major scale spread out as a stack of thirds (right).

Octave equivalence shows that ninths and seconds share interval classes, but to avoid muddiness, generally a ninth would be voiced at least an octave above the root. Similarly for elevenths (fourths) and thirteenths (sixths). For suspended chords, the term second or fourth would be used for those intervals. For major and minor chords that employ a sixth above the root, the term sixth would be used. For dominant chords, we see the term ninth and thirteenth used. For Lydian chords the note is called sharp eleventh instead of sharp fourth. But this is mostly just convention and nomenclature and doesn't effect the way chords and scales relate in terms of interval classes that are octave equivalent.

Avoid Notes

For a given mode, an avoid note refers to a 9, 11, or 13 scale degree that is generally not used to build compatible chords for the mode, and which is often avoided in the melody as a note to be held, but is of course allowed as a passing tone, as any chromatic note would be. (See also Playing Outside.) If one considers similar modes and chords, it may be possible to voice a chord for the mode that would allow for the avoid note to be played in the melody in the neighboring mode (reharmonization).

Avoid notes are listed on each mode page, for example, Mixolydian or C Mixolydian, each scale page, for example, F Major (Diatonic), and in the scale-tone chord tables (more below), for example All C Chords.

Diatonic Extended Chords or Scale-Tone Chords

This table lists scale-tone chords for the seven modes of the C Major diatonic collection, along with their avoid notes, sorted into columns by the highest degree used by each chord.

Diatonic

5 7 9 (or 2) 11 (or 4) 13 (or 6)
Avoid 11 (F)
Avoid 13 (B)
Avoid 9 (F), 13 (C)
Avoid 9 (F), 13 (C)
Avoid 11 (C)
Avoid 13 (F)
Avoid 9 (C)


The next section will continue to apply this approach to the modes of the other scales.