tritone substitution
A jazz harmonic technique in which a dominant seventh chord is replaced by another dominant seventh chord a tritone away
In Depth
Tritone substitution works because two dominant seventh chords a tritone apart share the same tritone interval (the third and seventh swap roles). In the key of C, G7 (containing B and F) can be replaced by D♭7 (also containing F and C♭/B). The substitution creates chromatic bass motion (D♭ to C instead of G to C), which many jazz musicians prefer for its smooth voice leading. Tritone subs are fundamental to bebop harmony and modern jazz arranging.
Thelonious Monk was among the first jazz pianists to systematically exploit tritone substitutions, creating his characteristically angular harmonic language.