Music theory is over complicating the study of jazz guitar and jazz improvisation in general.
Guitar teachers filling their curriculum with music theory have over complicated the study of jazz guitar. Students are left believing that the keys to performing jazz music are through the study of scales and modes. In addition, there are a plethora of music educational systems that further perpetuate the complication of the study of jazz guitar.
To fully understand how to play jazz guitar, one must study the forefathers of the jazz guitar and their approach to jazz guitar. Furthermore, one must also understand the difference between music theory and practical musical concepts. West Montgomery is considered one of the greatest influential jazz guitarists of all time despite not having the ability to neither read music nor have any musical theory training; however, he had an intimate knowledge of jazz harmony and block chords, which is the practical concept that all of the master jazz guitarist utilize.
Jazz guitar performing and solo improvisation has 0% to do with scales and modes and 100% to do with chords. The masters of jazz guitar play melodies and improvise on solos based off of chords with the understanding of chord tones not scale tones. For example, if a jazz guitarist solos over a progression of C Major 7 to Am7 to Dm7 to G7, he is literally seeing block chord shapes and chord tones of (C E G) to (A C E ) to (D F A) to (G B D) with an understanding of the non chord tones around them. Because they are visually seeing chord shapes and their fingers are playing on those chord shapes this allows for jazz guitarist to move freely up and down the guitar neck without having to think about what they are playing and rely solely on pure creation and inspiration. In addition, the jazz guitarist sounds in tune and melodic as well as sonically creating hills and valleys in their melodic lines.
Guitar players who rely on scales usually never sound melodic, and they run the risk of playing notes against chords that create harsh sounds. For example, in the key of C Major the C note will not work every time you play it. If you play it against a G chord you will hear an unpleasing sound of minor seconds between the B and the C notes. The same goes for an F note against a C Major chord. You will hear an unpleasing minor second sound between the E note and the F note. In addition, the key signatures of jazz standards are irrelevant as a result of the many non-diatonic chords within the song. Playing a C scale will further create harsh sounds if played against certain non-diatonic chords.
In summary, theoretically you can analyze any piece of music and the notes that make up the song and conclude an underlining scale motive. However, if you study the great jazz guitarist you will understand that their actual performance was based off the practical concept of playing on the chord changes and not playing scales. There is a huge difference between theory and practical concept.
In conclusion, the three simple practical concepts that all jazz musicians understand is:
1. Understanding chords and chord tones.
2. Understanding that 75% of the jazz standards runs the cycle of 5ths.
3. Conceptually viewing the I Major Chord and vi minor chord the same and ii minor chord and the V7 chord the same.
Here is a youtube video of Wes Montgomery supporting the musical concept of the above article. Watch his fretboard hand closely you will see his hand moving and outlining chord shapes not scales. His hand moves all over the guitar neck in barre chord locations. His hand does not move in a scale direction. http://www.youtube.com/watch?v=HFlTUEz0xpI