Sunday, August 19, 2012

Creston Chunks: Measure 4

[This post is part of my Personal Practice Project: Creston Chunks.]

Paul Creston's Sonata for Eb Alto Saxophone and Piano is 123 measures of interesting stuff. With (almost) no single measure repeating itself anywhere in the piece, each measure has its own special stuffsomething unique to study, analyze, and get under the fingers.

(Fortunately, there are a few motifs and harmonic ideas that show up with some frequency. For example, the piano accompaniment is comprised almost exclusively of seventh chords—primarily major-minor seventh chords.) 

With this "chunk" method, you become very well acquainted with each measure. It's almost as if each measure is its own little person with something unique to say.

Some have something interesting to say (m. 4), some have nothing to say (m. 35: a whole rest in both clefs), and some have a rather offensive message (m. 9: two sets of descending thirds, each a dissonant half step apart).

Meet measure 4 (and 5):

Essentially, measure 4 is an A7 chord. The 3rd (C#) and 7th (G) of the chord is maintained in the right hand, while the left hand covers the root (A) and the 5th (E).

In addition to featuring A7, the left hand hints at another chord. By moving a half step up from A and E, the left hand is playing Bb and Eb on beats 2 and 4. Combining these raised left hand pitches with the 3rd and 7th of the right hand, and by thinking enharmonically, we are able to derive another chord: Eb7.

So, in m. 4, both A7 and Eb7 appear. This is a great example of tritone substitution. A and Eb are separated by the interval of a tritone (an augmented 4th or a diminished 5th). The term tritone substitution refers to the fact that the two chords can easily substitute for one another. Why? Keep on reading!

When you have two dominant seventh chords whose roots are a tritone apart, something very cool happens: The 3rds and 7ths of their chords use the same pitches.

Let's look again at measure 4 to explore the tritone substitution. Thinking of A7, the 3rd of the chord is C# and the 7th is G. Now, thinking of Eb7 (beats 2 and 4, with Eb/D# being the root and Bb/A# being the 5th), Db (enharmonic to C#) is the 7th and G is the 3rd.

Put another way, the 3rd of the A7 is also the 7th of the Eb7, and the 7th of the A7 is also the 3rd of the Eb7.

This explains why the right hand is able to stay on the same notes despite the fact that two different chords are being created. Since the 3rd/7ths are shared between the two chords, it's up to the left hand to differentiate the chords by playing the root and 5th of the chords.

How exciting!

To summarize, measure 4 is pretty great. It exemplifies the tritone substitution beautifully (and it's quite fun to play).

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