Tritone substitution

In jazz music a tritone substitution is the use in a chord progression of a dominant seventh chord (major/minor seventh chord) that is three steps (a tritone) away from the original dominant seventh chord. For example, Db7 would be the tritone substitution for G7.

Related Topics:
Music - Chord progression - Dominant - Seventh chord - Steps - Tritone

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The reason a chord a tritone away may be substituted is because dominant seventh chords contain a tritone between their third and seventh members (B and F in a dominant seventh on G: G-B-D-F) and this tritone is shared with the dominant seventh chord whose root is a half octave away (from G, a dominant seventh on C#: C#-E#-G#-B or, enharmonically, Db: Db-F-A-Cb, E# = F and Cb = B).

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This substitution is particularly suitable for jazz because it produces chromatic root movement when applied to the ii-V-I progression prevalent in jazz tunes. For example, in the progression Dm7 - G7 - Cmaj7, substituting Db7 for G7 produces the downward movement D - Db - C in the roots of the chords, typically played by the bass. This also reinforces the downward movement of the thirds and sevenths of the chords in the progression (in this case, F/C to F/B to E/B).

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Tritone substitutions are also closely related to the alt chord used commonly in jazz. The alt chord is a heavily altered dominant seventh chord, built off a scale that includes a flat ninth, sharp ninth, sharp eleventh, no fifth, and flat thirteenth. For example, C7alt is built from the scale C, Db, D#, E, F#, Ab, Bb. Enharmonically, this is almost the same as the scale for Gb7, which is the tritone substitute of C7: Gb (=F#), Ab, Bb, Cb, Db, Eb (=D#), Fb (=E). The only difference is C, which is the sharp eleventh of the Gb7 chord. Thus, the alt chord is equivalent to the tritone substitution with a sharp eleven alteration.

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Classical theory would notate the "substitute" as an augmented sixth chord, specifically the enharmonically equivalent German sixth which serves as a substitute for the dominant of the dominant (V/V) (Satyendra 2005, p.55).

Related Topics:
Augmented sixth chord - Dominant

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Below is the original dominant-tonic progression, that progression with the tritone substitution, and the same progression with the substitution notated as an augmented sixth chord:

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Tritone substitutions are a common technique in jazz and were first used by musicians such as Duke Ellington, Art Tatum, Coleman Hawkins, Roy Eldridge and Benny Goodman. Tritone substitutions are a defining part of Coltrane changes.

Related Topics:
Technique - Jazz - Duke Ellington - Art Tatum - Coleman Hawkins - Roy Eldridge - Benny Goodman - Coltrane changes

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