• Jay EuDaly

The Tritone Substitution (1)

Updated: Sep 7, 2021

“The more you alter a Dominant chord, the more like its Tritone it becomes.”

With that one simple statement, my teacher (John Elliott) explained the Dominant Tritone Substitution; how it works and why it works.

Here’s a technical definition:

  • A Tritone Substitution is the substitution of one Dominant 7th chord (possibly altered or extended) with another (possibly altered or extended) that is three whole-steps (a tritone) from the original chord. It's also known as a Flat-5 Substitution, since a tritone is a flatted 5th (technically speaking, a Diminished 5th) from the original root.

So let’s test John’s maxim, “The more you alter a Dominant chord, the more like its Tritone it becomes.

We’ll start with an open-voiced Bb9:

The Tritone is E. We’ll use a close-voiced E9:

Both of these chords are unaltered. However, if we define the notes of the Bb9 in terms of E, that is, switch the root from Bb to E while leaving everything else the same, the E9 chord is double-altered, namely E7+(b9):

  • Note: the sharped 5th (denoted by the "+" sign), can also be called a, “b13.”

Now we’ll start altering the Bb9, then shift the root to E and see how the Eb7+(b9) has changed. The first thing we’ll do is flat the 9:

So it turns out that flatting the 9th of the Bb naturals the 5th of the E:

Both chords are now single altered; both are Dominant b9.

If we sharp the 5th of the Bb chord we’ve naturaled the b9 of the E:

If we flat the 5th of the Bb (the b5 can also be called a #11), that gives us the root of E, making the E chord an unaltered E7:

So in each case the Bb is now double-altered and the E is unaltered. If I go through every possible alteration of a Bb9 chord the result is always the same; it becomes more like an unaltered E9, E7 or E13. Therefore: