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.1

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.2