Tritone substitution
Any dom7 chord can be substituted by a dom7 chord that has a root a tritone away – hence, tritone substitution. This works because this pair of chords share the same tritone.
This is also called a substitute dominant.
Examples:
- G7 —> Db7 (B, F)
- C7 —> Gb7 (Bb, E)
- Eb7 —> A7 (G, Db/C#)
The roman numeral notation is subV/X, so if we had a tritone sub for V7/VI it would be subV7/VI.
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