In classical music, a substitute dominant is "a chord sufficiently akin to the dominant to be reasonably set against the tonic, and yet remote enough to give a chromatically expressive, large-scale dissonance to the structure".[1] For example, using C major instead of E major in the key of A major.
In jazz, a tritone substitution[2][3] (tritone substitute dominant[4][5] or substitute dominant[2][6][7][8]) is the chord substitution of a chord with a dominant chord that has its root a tritone away from the original. The tritone substitution is one of the most common substitutions found in jazz and was the precursor to more complex substitution patterns like Coltrane changes. Tritone substitutions are sometimes used in improvisation — often to create tension during a solo. They were first used by musicians such as Dizzy Gillespie in the 1940s,[9] Duke Ellington, Art Tatum, Coleman Hawkins, Roy Eldridge and Benny Goodman.
Contents |
A substitute dominant is a chord substitution for a chord with a dominant function. Barbara Barry explains:
In the hierarchical organization of key, other degrees may be regarded as having dominant function, for example, the mediant, which can act as a 'second order' dominant, the supertonic, as supportive as a secondary dominant, or the leading note triad. Their ability to define key, though, is less strong than that of the dominant, as is clear when the dominant is present.[10]
However, David Epstein disagrees:
...[placing the second theme group in the mediant] suggest[s] that the mediant served as a 'substitute' dominant. Perhaps so, as a locale for stating subsequent themes. As a substitute tonal function, however, the mediant-as-substitute-dominant theory seems improbable, given the tendencies of tonal behavior. For in major keys the mediant major is twice indirectly removed from the tonic, only three pitches out of seven being common to the two keys.[11]
A tritone substitution is the use in a chord progression of a V7 (dominant seventh chord) (major/minor seventh chord) that is three whole steps (a tritone) from the original chord. Using simpler analytic music notation, a tritone substitution involves replacing V7 with ♭V7/V = ♭II7[2] = subV7[2] (even V7/♭V[2]). For example, D♭7 is the tritone substitution for G7.
From traditional jazz harmony, tritone substitution works because the two chords share two pitches: namely, the third and seventh, albeit reversed.[13] In a G7 chord, the third is B and the seventh is F; whereas, in its tritone substitution, D♭7, the third is an F and the seventh is C♭ (enharmonically B). Notice that the interval between the third and seventh of a dominant seventh chord is itself a tritone.
Edward Sarath calls tritone substitutions a "non-diatonic practice that is indirectly related to applied chord functions... yield[ing] an alternative melodic pathway in the bass to the tonic triad."[2] Patricia Julien says it involves replacing "harmonic root movement of a fifth with stepwise root movements (e.g., G7-C becomes D♭7-C) so that although stepwise root movement is involved, the relationship between the chords is functional."[14].
The tritone substitute dominant often contains the dominant pitch due to its importance melodically and tonally, and this is one of the ways in which substitute dominants sound and function somewhat differently than conventional dominant chords.[5] The substitute dominant may be used as a pivot chord in modulation.[15] Since it is the dominant chord a tritone away, the substitute dominant may resolve a tritone above the previous tonic (for example, in F one may feature a ii-V on C, which with a substitute dominant resolves to G♭, a distant key from F).
Classical harmonic theory would notate the substitution as an augmented sixth chord on ♭2. The augmented sixth chord can either be the Italian sixth It+6, which is enharmonically equivalent to a dominant seventh chord without the fifth; the German sixth Gr+6, which is enharmonically equivalent to a dominant seventh chord with the fifth; or the French sixth Fr+6, which is enharmonically equivalent to the Lydian dominant without the fifth but with a sharp eleven, all of which serve in a classical context as a substitute for the secondary dominant of V.[16][17]
Below is the original dominant-tonic progression, the same progression with the tritone substitution, and the same progression with the substitution notated as an Italian augmented sixth chord:
One of the most common usages of the tritone substitution is in the 12-bar blues. Shown below is one of the simpler forms of 12-bar blues.
I IV I I IV IV I I V IV I I | C7 | F7 | C7 | C7 | F7 | F7 | C7 | C7 | G7 | F7 | C7 | C7 ||
Next, here is the same 12-bars, except incorporating a tritone substitution in measure 4; that is, with Gb7 substituted for C7.
I IV I bV7 IV IV I I V IV I I | C7 | F7 | C7 | Gb7 | F7 | F7 | C7 | C7 | G7 | F7 | C7 | C7 ||
The second common usage of the tritone substitution is in ii-V-I progression, which is extremely common in jazz harmony. This substitution is particularly suitable for jazz because it produces chromatic root movement. For example, in the progression Dm7 - G7 - Cmaj7, substituting D♭7 for G7 produces the downward movement of D - D♭ - 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 altered chord used commonly in jazz. Jerry Coker explains:
Tritone substitutions and altered dominants are nearly identical... Good improvisers will liberally sprinkle their solos with both devices. A simple comparison of the notes generally used with the given chord [notation] and the notes used in tri-tone substitution or altered dominants will reveal a rather stunning contrast, and could cause the unknowledgeable analyzer to suspect errors. ... the distinction between the two [tri-tone substitution and altered dominant] is usually a moot point.[3]
The alt chord is a heavily altered dominant seventh chord, built on the alt scale, a scale that includes a flat ninth, flat third, flat fourth, flat fifth, flat sixth and flat seventh. For example, C7alt is built from the scale C, D♭, E♭, F♭, G♭, A♭, B♭. Enharmonically, this is almost the same as the scale for G♭7, which is the tritone substitute of C7: G♭ (=F♯), A♭, B♭, C♭, D♭, E♭ (=D♯), F♭ (=E). The only difference is C, which is the sharp eleventh of the G♭7 chord. Thus, the alt chord is equivalent to the tritone substitution with a sharp eleven alteration.
The tritone substitution primarily implies a Lydian♭7, or Lydian dominant scale. In the case of C7 to Bmaj7, the implied scale behind C7 would be C D E F♯ G A B♭. Because of this, the extensions of 9, ♯11 and 13 are all available, while the ♯11 is where it shares with the altered scale.