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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 whole steps (a tritone) away from the original dominant seventh chord. For example, Db7 would be the tritone substitution for G7.

The reason these dominant seventh chords may be substituted for each other is that they share the two pitches that form a tritone in each chord (the third and seventh, albeit reversed). In a G7 chord, the third is B and the seventh is F. In the Db7 chord, the third is an F and the seventh is Cb (enharmonically B). Note that the interval between the third and seventh of a dominant seventh chord is itself a tritone.

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).

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 of the alt scale that includes a flat ninth, sharp ninth, flat fifth, sharp fifth, and flat seventh. For example, C7alt is built from the scale C, Db, D#, E, Gb, G#, 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.

Classical harmonic 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), sometimes referred to as "the German Augmented sixth on b2".

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:

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 subtitutions are also known as substitute dominants, or Sub-V (Sub-five) chords.

• Stein, Deborah (2005). Engaging Music: Essays in Music Analysis. New York: Oxford University Press. ISBN 0-19-517010-5.
  • Satyendra, Ramon. "Analyzing the Unity within Contrast: Chick Corea's Starlight".

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