---
title: Tritone Substitution
category: Jazz Harmony
slug: tritone-substitution
related: [ii-v-i, seventh-chords, reharmonization]
url: https://fourthshub.com/docs/tritone-substitution
---

# Tritone Substitution

A **tritone substitution** replaces a dominant 7th chord with another dominant 7th chord whose root is a tritone (6 half steps) away. It is one of the most powerful and frequently used reharmonization techniques in jazz.

## How It Works

Take G7 (G-B-D-F). Its tritone — the interval between the 3rd (B) and 7th (F) — is the source of its tension and its drive to resolve to C.

Now take Db7 (Db-F-Ab-Cb). Its tritone is between the 3rd (F) and 7th (Cb/B). **The same two notes** — B and F — appear in both chords, just with swapped roles (the 3rd of one is the 7th of the other).

Since both chords share the same tritone, they resolve to the same place. But Db7 approaches C from a half step above instead of a fifth above, creating a smooth chromatic bass line: Db -> C.

## The Classic Application

Original: Dm7 - G7 - Cmaj7 (ii - V - I)
Tritone sub: Dm7 - Db7 - Cmaj7 (ii - bII7 - I)

The bass line changes from D-G-C to D-Db-C — a smooth chromatic descent. The upper voices can remain essentially the same because of the shared tritone.

## Why It Sounds So Good

Three reasons:

1. **Chromatic bass motion**: Half-step bass movement is the smoothest possible approach to a resolution target.
2. **Shared tritone**: The essential tension notes are preserved, so the resolution still "works" harmonically.
3. **New color**: The bII7 chord introduces notes (b9, #11 relative to the original V7) that add harmonic richness.

## Extended Applications

**Tritone sub of V/V**: In a ii-V-I, you can tritone-sub the secondary dominant too. A7 -> D7 -> G7 -> C becomes A7 -> Ab7 -> G7 -> C.

**Chain of tritone subs**: Create long chromatic lines by alternating original dominants and their tritone subs.

**Tritone sub ii-V**: Replace the whole ii-V with the tritone sub's ii-V: Abm7-Db7 instead of Dm7-G7, both resolving to C.

## On Guitar in P4

The shape of a dominant 7th voicing and its tritone substitution are closely related on the fretboard. In fourths tuning, you can see the geometric relationship directly: the tritone sub is always the same shape shifted by 6 frets (half the fretboard).