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©2000 James Walker (This lesson is the third of three lessons dedicated to the subject of reharmonization.)
Last month's lesson focused on ways to reharmonize a passage by adding chords to a progression. The lesson below presents options for replacing one chord with another.
DERIVING SUBSTITUTE CHORDS FROM THE ORIGINAL HARMONY One may alter the original harmony of a composition by substituting one chord for another. Sometimes, the new chord may be directly related to the original; other times, the new chord may have no direct connection. The structure of chords indicates some common substitutions. Observe that the upper four pitches of a Cmaj9 chord are equivalent in structure to an Emin7 chord:
So, substituting Emin7 for Cmaj9 will utilize a new color (minor sonority vs. major) whose root (E) is a major third above the original chord (C), but remaining connected to the original harmony. Here are some other examples utilizing this same principle: (original chord progression for this example: Dmin7 | G7 | Cmaj7)
Dominant chords offer an even greater number of options in terms of chord substitution. Probably the most common is tritone substitution. Basically, any dominant chord may be replaced by another dominant chord whose root is a tritone away. (Note that the guide tones in the following examples, though spelled enharmonically to reflect the different dominant chords, follow the same voice leading in each example:)
DERIVING SUBSTITUTE CHORDS FROM A COMMON SCALE
It is also common to use a "diminished sound" on a dominant chord, by lowering the 9th by a half-step. This new chord lends itself well to the use of the diminished scale:
...and note the above example that the third, fifth, seventh, and ninth of this G7(b9) chord, taken alone spell out a B diminished seventh chord. This is also a common substitution for a dominant chord:
Taking this diminished scale a step further: the diminished scale is a "symmetrical" scale, created through a the repeated use of alternating major and minor thirds. This structure results in a scale which lends itself to a certain harmonic ambiguity. In the case of the diminished scale, this results in one scale with four different roots, minor thirds apart (i.e., the B diminished scale is the same scale as the D, F, and Ab diminished scales). Let's return to that G7(b9) chord, a dominant chord utilizing the diminished scale/sound. Using that same sense of ambiguity associated with the diminished scale, one may replace the G7(b9) chord with similar dominant seventh (flat nine) chords, built minor thirds apart: Bb7(b9), Db7(b9), E7(b9).
A similar example may be found with another variation on the dominant chord/scale relationship: the altered dominant scale (also referred to as the "diminished/whole-tone" scale). An altered dominant scale is a mode of the melodic minor scale (specifically, the ascending form of the scale):
...and the dominant chord derived from this scale is G7(#9/#5) (9th may also be lowered to become the b9). It is commonly (but not exclusively) used in minor keys.
Finally, it is possible to take another chord derived from the modes of the melodic minor scale, and substitute it for the dominant in this progression; it is a different sonority, but it shares the same scale (thus, a common tonality) with the original chord. Here, a Bmaj7(#5) chord has replaced the G7(#9/#5) - both are derived from the Ab melodic minor scale.
(This page and all the materials within copyright ©2000 James Walker, All Rights Reserved. No portion of this page may be duplicated or distributed without the author's written consent.)
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