It was when I picked up some David Baker books on bebop scales back in my junior year in college that I finally began to make some sense out of how jazz worked. Nobody had told me that one of the secrets of those bop musicians was to smooth out the seven-note scales and modes by interpolating an extra note–typically a raised seventh in Mixolydian modes and a raised fifth, or flatted sixth, in the tonic major scale. Once I latched onto that concept and began to flesh it out with various licks from Baker’s great publications, things slowly began to gel for me.

The thumbnail your right shows a G major bebop scale, with the D#/Eb serving as the raised fifth/flatted sixth. Click on the image to enlarge it.

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NOTE: All examples on this page are in the key of G major. Because note function changes relative to chord function, all references to the flat sixth in the following discussion are understood to mean the flat sixth of the major bebop scale.

The flat sixth most likely came into use as a passing tone designed to create an eight-note scale which could smoothly take a player from tonic to octave. But the note has applications that make it useful as more than just a linear connecting device, and I suspect that its insertion into the major scale also involved harmonic considerations. Chordally, the flat sixth of the major bebop scale helps define structures that a jazz improviser regularly encounters.

The most apparent harmonic use of the flat sixth, as the flat sixth (or flat thirteenth) of a tonic major chord, is not as common as other applications. But it is nevertheless an interesting and colorful tone which imparts an augmented sound to the tonic chord–a suspended sound that wants to resolve downward to the fifth. The second example on this page outlines a GMb6 chord, ending in a lick that emphasizes the b6.

The flat sixth crops up much more often as a minor third of the IV chord. It’s common to encounter a change of modality from major to minor in the IV chord, and the flat sixth is the tone that establishes this shift. The third example shows both CM7 and CmMaj7 chords. It’s common, in the shift from major to minor, to also lower the seventh, as shown in the bebop lick that’s included in the example.

Another extremely common use of the flat sixth is as the flat nine of a V7b9 chord. This next example outlines a D7b9 chord. Because the V7b9 is so ubiquitous in jazz, the flat sixth, far from serving as merely a passing tone, can often become a target tone. Also, as indicated at the end of the example, it can serve as a chromatic bracketing device.

The final example shows how the b6 fits into a V7b9 lick.

The harmonic applications of the flat sixth that I’ve just described are just three of its uses. It also functions as the b5 of a IIm7b5 chord; as the major third of the V7 of VI chord (ex. B7 in the key of G); and in other borrowed-chord applications that easily relate to the tonic key.

I’ll leave it to you to figure out the rest. This article should give you a good start. If you enjoyed it, be sure to check out other articles of interest to saxophonists and jazz improvisers on my jazz page.