We've talked about harmonic function frequently, and while it's an important tool in understanding the musical construction, let alone essential in effective improvising, we still have to remind ourselves they call it music theory, not music science. Composers worked within the "rules" and practices of their day, but it's important to keep in mind, most of the conventions were contrived and dissected in retrospect. In other words, creative musicians composed, and theorists went back with analysis after the fact. We doubt Bach wrote music "dictated" by rules, but his music contains decipherable practices and "formulas."

With that caveat as a backdrop, it's fun to look at a particular chord that has two different musical "functions." If you recall, we can simplify chords into three categories (a fourth "Hybird" but we don't need to go there now): Tonic, Dominant, and Dominant Preparation. (Check out our inaugural issue of MandolinSessions.com, Understanding the 'ii V7 I' Progression.) Tonic is easy; that's your home key. Dominant is variations of the chord based on the 5th Scale degree, and Dominant Prep is a chord or chords that set up for the Dominant.

Those who studied music theory in classical and "traditional" institutional contexts know that the 7th chord based on the Major scale is called a half diminished. In the key of C major, it would be B, D, F, A. It has the propulsion of a Dominant 7th chord, and if you looked at its construction (let alone listened to it sound), you'd see the three notes it has in common with the dominant 7th (G, B, D, F). In essence, it's a rootless Dominant 9th chord.

In C minor, the chord based on the second scale degree has a similar relational make-up, D, F, Ab, C, the half diminished, but being the ii chord, it doesn't function as a Dominant, rather it prepares the Dominant, G B D F. What's interesting is in jazz circles, the ii half diminished 7th is always referred to as a minor 7th chord with a flatted fifth.

Dm7b5

This makes a lot of sense as its function is more as a minor chord (Prep) than a diminished (Dominant). Even your casual jazzer will label these chords as m7b5, and it helps to arm yourself with different inversions or grips at your fingertips, especially if you want to enjoy playing in minor keys, or want to effectively communicate 'ii7b5 V7 I' progressions or tonal centers. We have some of these in our ii V7 I Home Positions page.

Next week, we'll bring you even more transposable ii7b5 grips from the pros, so stay tuned.

Further:
Functional thinking...
Circle of Fifths
ii7b5 V7 i Minor Patterns

Posted by Ted at March 5, 2009 1:05 PM