With that in mind, consider the relationship between the bass (upright, bass guitar, etc.) and the chord. The chord can now expand beyond a single instrument. For example, a Dm7b5 played on the guitar paired with a Bb bass note becomes a Bb Dominant 9th chord. I hear the total combination of the two primarily, not just the separate chord(s) or intervals unless I really try. Now think about melodies (and counter-melodies/harmony melodies) in play on top of the chord(s) and bass-line. This adds to the total tonality or quality at hand. If the bass, chord, and melody all come from the same “parent scale/mode” there is a huge amount of harmonic cohesion. As pattern-seeking creatures it makes sense that humans get excited when this kind of structure is heard, even if it is not fully grasped. Think of fractal patterns in digital art; we do not see the math, just the beautiful eye-candy results. Harmonic structures are a part of our Western cultural tradition, and are somewhat based on our subtle perceptions of the overtone series found in acoustics. Through repeated exposure to the overtone series we started actually adding the “phantom intervals” into the music in acceptable ways; the perfect 5th, then the 3rd, and so on. This eventually opened the floodgates for triads, seventh chords, and extended chords. If chords and/scales are played simultaneously and they are not harmonically related we generally find it to be a “challenging listen”. Think of some of the bi-tonal/atonal piano sonatas of Charles Ives! These challenges can be exhilarating at times and extremely unpleasant at others. It takes a certain personality to enjoy them, and I am not usually one of them.
Having an acute sense of “relative pitch” capable of hearing the Gestalt in homophonic music lead me to thoroughly analyze scales and chords, and especially their tonal relationships with one another. I started by examining every diatonic chord possibility. This included exploring all of the possibilities within each of the seven diatonic modes. One of the most interesting results I found was that all of the notes generally sounded acceptable in some context except for notes that were one half-step above the underline triad if they are played on harmonically strong beats. This explains the “avoid” note concept because a dissonant interval of a minor 2nd (or minor 9th) is in play against a foundational triad chord tone (root, 3rd, or 5th). This sounds dissonant in an undesirable way, compared to other intervallic modal tensions, which are often the favorite note choices of jazz musicians.
I also seriously considered “implied harmony”. For instance, a melody that clearly outlines an arpeggio, or a good walking bass line, etc. Interestingly enough, my own developmental guitar practice was primarily unaccompanied by another instrument or recording (except for a metronome). In order for me to really hear the underline chord changes, I intuitively started building “compound melodies”. The implied counterpoint within my lines made having a chordal instrument play behind me somewhat unnecessary. When I finally formed a working trio with an upright bassist and drummer we were all amazed that the extended chords and advanced jazz harmony was fully realized without having to play the guitar in an athletic chord-melody style. The three lines were enough (bass + my harmonically specific compound melodies). This led me to further study “linear harmony” and I found I was in good company with many of the classic bop and post-bop horn players, such as Bird, Clifford Brown, Sonny Rollins, etc (not that I clam to be on their level of mastery). My modal ideas were akin to Miles Davis and the modal concepts of the late 50’s and 60’s. Modal partial voicings like those of Bill Evans, McCoy Tyner, and Herbie Hancock also made a lot more sense to me than the typical approach used by guitarists (which includes bass notes, complete lower structures, and a few extensions). I feel that guitar chords do not have to say it all at once! I prefer to let the voicings state the modal harmony over time and to make good use of the rhythmic space that way.
Playing “outside” (meaning to play in a second tonality for a temporary period before resolving back inside) did nothing but confuse the overall sound of my project. For example, since six or seven out of twelve modal notes sound harmonically descriptive the remaining few sound like “wrong” notes if they are in the place of “guide tones” to me. I do believe however, that all twelve notes in music can be played over any given chord if they are emphasized (or de-emphasized) in a precise and “inside” manner. There surly are masters of playing outside in classic jazz, like Herbie Hancock, Coltrane, and Eric Dolphy. I just have not reached that point on the guitar yet, and I may never. Who knows!
After years of experimentation I found only handful of scales that widely acceptable harmony could be drawn from. The diatonic system, the Phrygian dominant mode (with an extra #9th between the b9 and major 3rd), the melodic minor system, the whole-tone scale, and the “half-step whole-step” version of the diminished octatonic scale. Any scale that has a degree one-step-and-a-half or larger I consider an “abbreviated scale” (i.e. pentatonic scales and hexatonic scales, etc.). For this reason I also found the harmonic minor and major scale somewhat flawed except for Phrygian dominant with a sharp ninth added back in. Other scales such as the bebop and blues scale, I disqualified as true harmony-building scales because the extra note involved in each is merely a passing tone and cannot be used as a modal root from which to build structures.
Though harmony is usually considered the vertical aspect of music it is important to remember that it is time-sensitive and is interpreted horizontally for a limited duration of time as well. We take what we hear in sequence and reorganize it almost as if it were played simultaneously. This obviously has an huge influence on melodic outlines and partial chord voicings played in sequence with in a given amount of time or measures.
Being guitarists we often get proud of particular part in a musical performance and we assume because our part worked and had logic to it that the homophonic result of the ensemble was altogether successful. We often do not take into consideration what notes and scales the bassist or the other melody instruments at the same moment. There is often too much going on to be able to do so in real-time with much accuracy. If we were to go back and analyze all of the parts and the incidental counterpoint/group-harmony we may cringe at the results. By using the standard Roman numeral system and vague chord symbols jazz musicians are typically free to interpret the harmonic structure of a given song very loosely. If two or more musicians choose alternate routes over a series of chords there is an extremely low probability that the counterpoint/group-harmony created between them is on par with a simple prearrangement or a same-mode approach. This restricts the use of certain passing chords and alternate scales for obvious reasons. I feel that there is a huge amount of creative material to be found within each chord-scale, and that it is arrogant when jazz musicians insist on playing “outside” because they feel they have completely exploited playing inside and have no place else to go.
In order to improvise a large amount of harmony and motion without a huge amount of muddled mix-matched moments, some theoretical guidelines must be employed. I truly believe in a simple system where each musician creates parts from the same modal palette (within one beat of each other), and that it has an extremely high probability of real-time harmonic cohesion. This method has become the basis of my group and compositional/arranging style. I write modes where chord symbols usually go on my charts, original or otherwise. In my combo improvised reharmonization is not allowed, whereas substitution using the same mode is strongly encouraged. The result is exceptionally structured music that is constantly fresh sounding and easy to navigate through as a musician. That’s my ear and my sound thus far.