Creating new interpretations of old favorite tunes is one of the cornerstones of jazz, and because of this, the concept of chord substitutions is extremely important. Substitutions provide a way for performers and arrangers to put a new spin on more well-trodden harmonic progressions. This chapter uses the turnaround as a basic progression to be altered, but these substitutions can be applied anywhere in a harmonic progression.

Applied Chords as Substitutions

As discussed in the Tonicization chapter, an applied chord can be productively related to the diatonic chord with which it shares a root note.

Because root motion by fifth is extremely common in jazz, there are many opportunities for performers to simply substitute the first chord in a fifth-wise chord progression with the dominant seventh built on the same root. One especially common place where this is implemented is in the turnaround, where, because each chord is related to the next by fifth, a chain of applied V⁷s is a common variant (Example 1).

Example 1. When a progression has root motion by fifth, the quality of the first chord can be changed to dominant seventh in order to transform it into an applied V⁷.

Mode Mixture

“All of You” by Cole Porter is a composition that has mode mixture built into it. Listen to this recording by Ella Fitzgerald (transcribed in Example 2), conveniently in C major, and observe how the alternation between A♮ (la, [latex]\hat6[/latex]) and A♭ (le, [latex]\downarrow\hat6[/latex]) catches the ear and imbues a sense of sentimentality in the song. A♭ here can be understood as being borrowed from the parallel minor (C minor), a practice known as mode mixture.

Example 2. “All of You” by Cole Porter uses a minor iv chord (Fmi) and a half-diminished ii chord (D^∅7) even though the tonic is major.

Many songs, like “All of You,” have mixture built into their chord structure. But mixture chords can also work as improvised substitutions: a chord within a diatonic chord progression can be substituted with its minor-mode variant to produce a color change that won’t change the overall function of the chord. A mixture substitution works best when the scale degree being inflected is la [latex](\hat6)[/latex], and is therefore being transformed into le [latex](\downarrow\hat6)[/latex]. As an example, consider the turnaround in Example 3: instead of a diatonic version, one may choose to incorporate le [latex](\downarrow\hat6)[/latex] to generate some more colorful harmonies. These particular substitutions—changing a ii⁷ to a ii^∅7, and a G⁷ to a G^7♭9—are particularly common uses of mode mixture in jazz.

Example 3. Mixture chords are most effective when they involve [latex]\mathit{\downarrow\hat6}[/latex]. Mixture and diatonic versions of the same chord have the same function.

Tritone Substitutions

While the above methods of substitution are common in pop and classical styles as well, the tritone substitution is unique to jazz. Tritone subs take the place of V⁷ chords, either applied or diatonic. The “tritone” part of the name comes from two key roles of tritones in these substitutions:

1. The substituted chord is a tritone away from the chord it is replacing.
2. The chords are related because they share the same tritone.

This relationship is best explained graphically, as in Example 4: because the tritone evenly divides the twelve-tone collection, transposing by tritone maps the tritone onto itself. Speaking practically, the bottom line is that any dominant seventh chord can be replaced by the dominant seventh chord a tritone away, and the progression still functions the same way.

One way to recognize a tritone sub is by its chromatic resolution downward by a minor second.

Example 5 shows how tritone substitutions are commonly used in the turnaround.

• As discussed above, it’s common to replace the diatonic chords with applied chords that share the same root, yielding a progression consisting entirely of V⁷ chords—this is shown in the right-hand harmonization on the top row.
• From there, tritone substitutions can be used for any V⁷ chord.
• Most commonly, every other chord is replaced with a tritone sub, yielding a chromatic bass line and smooth voice leading, as in the bottom row of harmonizations.

Example 5. Because tritone substitutions can replace any applied dominant chord, in progressions moving by fifth like the turnaround, chords may first be (conceptually) substituted with their applied variants, and then tritone substitutions can be used to create a chromatic bass line.

The ii–V–I chapter visualized the ii–V–I schema within a voice-leading space constructed by Michael McClimon (2017). McClimon further visualizes the tritone substitution as a kind of shadowing space behind the typical ii–V space (Example 6). Click here to view his animation of the progression of “Blues for Alice” and its movement through the ii–V space with tritone substitutions. Notice that the tritone-substituted V⁷ chord is preceded by its ii⁷ chord, and that both chords are in the green space that McClimon places behind the foreground ii–V space.

Substitutions in a Lead Sheet

As with embellishing chords, substitutions are not always represented the same way in a lead sheet.

• There may not be any substitution notated, and instead the performers are improvising this addition as they play.
• The substitution may be built into the chord progression and thus be notated in the chord symbols.
• The substitution may be indicated as an alternate harmonization and shown in chord symbols with parentheses around the substituted chords.

This is illustrated in Example 7, with different ways of showing a modally mixed ii^∅7 chord in “Satin Doll” by Duke Ellington.

1. Bebop composition. Asks students to build on knowledge of swing rhythms, ii–V–I, embellishing chords, and substitutions to create a composition in a bebop style.
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