from Hal Leonard Guitar Method: Jazz-Rock Fusion (00697378)
Interval Structures
Chords forms may also occur based on an interval pattern outside of the conventionally stacked 3rd forms. Quartal voicings are forms built on a pattern of 4ths. They occur as either pure 4ths, in which only the interval of a perfect fourth exists between chord tones, and diatonic fourths, which incorporate a different interval in combination with 4ths to accommodate a certain relationship. The diatonic fourth forms below illustrate the incorporation of an augmented 4th. However, any interval may be coupled with 4ths to form different chords.

These forms can function as several different chords depending on what note of the form is determined to be the root. In the following figure, they function in one of their most common roles: m11 chords. [Download audio sample]

The root of a chord form may also be a surrounding note not in the form. In cases such as these, it’s nice to have a bass player on hand to cover the root. In the following figure, the last of the previous diatonic 4th forms is shifted to various spots along the neck to play each of the “B” chords, with the roots of Bm6/9, B7#9#5, and B13 not directly contained in the form. On the accompanying track, the bass drones a B root throughout the progression. [Download audio sample]

The former figure illustrates how a single chord form can actually function as several different chords. It all depends on what note is determined as the root. With twelve notes in western music, this means that a chord form will have twelve possible roots it can relate to. This is a hip understanding to apply in your playing. Not only can you use a single form to play a number of different chords (making certain chord changes easier to play), but you can also create some voodoo sounding approaches to voicing a given set of chords. The following forms illustrate a few of the multiple functions they can serve. The notes included in each form occur above the chord diagram and how those notes function in relationship to different roots, as well as the chord they generate, are shown beneath.

The key to grasping the “relative possibilities” for a given chord form is to know the notes it consists of and how those notes relate to the twelve keys of western music. The following figure presents each of the fifteen major keys (or scales) with their degrees for the twelve notes of music—all formed by starting the major scale formula from each note.

Why fifteen for twelve, you may ask? There are fifteen because the B major, F# major, and Db major scales can also be written as Cb major, Gb major, and C# major, respectively. These are known as enharmonic spellings. Simply, enharmonic means the same note with a different name. Learning these scales and understanding the multi-functionality of different forms seems like a daunting task, but it’s also one of the single most important ways to blow your awareness of chords and music out of the stagnant “loss-of-ideas” and “I-keep-playing-the-same-form” waters. One scale/key at a time is all it takes. Remember that, in the following scales, the degrees 2, 4, and 6 also function as 9, 11, and 13.