Tritone Substitution
Replacing a dominant seventh with one a tritone away
Related
Tritone substitution replaces a dominant seventh with another dominant seventh whose root lies a tritone away. In C major, D♭7 may take the place of G7: the two share the same tritone, but the third and seventh swap roles.
The substitute bass often falls by a semitone to the root of its target chord, which smooths the voice leading. The device is common in jazz and also works on secondary dominants; the symbol takes the new root, while the function keeps the old direction of resolution.
It differs from the Neapolitan chord on the flat second: that is a major triad, usually a predominant, whereas a tritone substitute is a dominant seventh acting as the dominant. Both put a flat second in the bass, but their quality and resolution differ.
Sources
- 三全音替代的构造与解决，参 The New Grove Dictionary of Music and Musicians, "Harmony"；本文为原创表述
Used for fact-checking only; all prose is original.