Dahnielson

Reharmonization

Any chord can be substituted for another which has the same tonic, dominant or traveling function as we have already seen with the parallels.

A substitute chord, or series of substitute chords, can provide alternate harmonic paths while maintaining its original function. Four types of substitutions which occur frequently in jazz are the tritone substitution, the omitted root substitution, cycle of fifths progression additions, and leading chord progression additions.

Tritone Substitution

One of the oldest tricks in the book also known as flattened fifth substitute or simply b5. It let you substitute dominant chords to do smooth voice leading.

The substitute chord is a dominant 7th chord whose root is a tritone, three whole steps (six semitones), away from the original dominant 7th chord. They are interchangeable because the pitches of the tritone is identical.

The example above show that the substitute chord for G7 is a Db7. Taking a closer look we can see that the interval between the originals root and the substitute is a tritone either way, and that the tritone interval are the same in both chords (F and B).

By using the tritone substitution, the roots of the II-V-I progression can move down by semitones, instead of ascending 4ths. For example, in C major:

Rather than keeping the typical Dm7-G7-Cmaj7 progression.

Omitted Root Substitution

This substitution exchanges the root of the given chord for a root a 3rd or 5th higher. The substituted chord still retains several pitches of the original, implying the same harmony, but can also point toward different directions, both in key and function.

For example, B depicts a G7 chord with various omitted-root substitutions. The Bdim7 chord, with 3 pitches in common with the original, retains the dominant quality, as it contains two tritone intervals. At first glance it seems to share an identical function with a G7 chord, yet, because G is omitted as the root, the diminished 7th chord offers additional possibilities of resolution. In short, unlike G7, Bdim7 is as likely to resolve to Amaj7 or Ebmaj7 as Cmaj7.

The G7 and Bb7 chords have two pitches in common and, along with their dominant 7th constructions, generate enough similarity to share a dominant function but also enough diversity to provide pathways in different directions. (The obvious resolution of Bb7 is in the key of Eb and the G7 is the dominant of C.)

Because of common pitches and the presence of a tritone, Dø can also be a dominant substitute for G7. At the same time, however, its root, a fifth higher, also has a traveling function. As the ii chord in the key of C, the Dø (with its altered 5th) allows the progression to extend itself before progressing toward a dominant and eventual tonic.

Cycle of Fifths Progression Addition

The cycle of fifths, as well as being fundamental to the structure of many jazz composition and inserted as turnarounds, can also be used as a series of substitute chords in specific parts of a composition.

Leading Chord Progression Addition

A leading chord is a 7th chord that is a semitone above the chord you want to go to.

In classical music you learn about leading tones, these notes lead into the next melody note, but are not necessarily an integral part of what is going on. They are more of an embellishment to what is really important, like the melody. If we reharmonize with leading chords, we are not changing the music in such a way that it ruins it, we are simply adding a bit of tension for a moment until we get back to the chord everyone expected us to get back to.

There will be times that you’ll need to make the leading chord a minor 7th, or something else, but obviously you will need to practice this on your own to get comfortable with it.