The Tritone Substitution (SubV7)

A Tritone substitute (also called SubV7) is a chord swapping technique that enables you to swap a Dominant 7 chord with another Dominant 7 chord one Tritone away.

You can use that technique in harmonizing and while soloing.

If you’re a Jazz player that’s definitely a subject you have to master but I actually recommend every musician to study these techniques.

These concepts go way beyond Jazz, these are the workings of harmony. Understanding these tools will be useful no matter what genre you’re playing or what instrument!

In order to understand what is a Tritone Substitution, we need to first understand what is a Tritone!

The Tritone

A Tritone is a musical interval. It consists of 3 whole tones and divides the octave right in the middle.

For example, let’s take C as an anchor note and build an ascending 3-tone interval from it. Our goal note, in this case, is F#, if we’ll build a descending Tritone from C we will also get to F#.

The Tritone carries a lot of tension in it and that tension desires to be resolved. Interestingly, it can be resolved in two directions. Let’s look at the following example.

Try to play this and hear for yourself this sense of resolution when we go from a Tritone to a major 3rd minor 6th.

* A Tritone can also be called an augmented 4th or a diminished 5th (for more info about intervals check "Musical Intervals Explained". 

Now… What is Sub7?

The “Sub” stands for substitution and the “7” refers to a Dominant 7 chord.

This means that we take the Dominant 7 chord of a certain scale and substitute it with another Dominant 7 chord located a Tritone away.

For example, let’s take G7 as our target chord, when we go a Tritone above it (or under) and build a Dominant 7 chord from this root, we get the Db7 chord.

The Db7 chord is the Sub7 of the G7 chord!

Now let’s understand the theory behind it:

* Before diving deep into this subject, make sure you have the background knowledge you need in order to understand everything, we recommend you to check out “Harmonic Function” before proceeding with this article.

Let's Proceed...

In order to understand the mechanism behind this chord exchange, we need to first look at the defining notes of the chord. These notes are the 3rd and 7th degrees of the chord. The 3rd degree “decides” if the chord is major or minor and the 7th degree alters the function of it by creating the b7 degree.

Let’s take G7 as an example, the 3rd degree is B and its 7th degree is F

The 3rd and the 7th notes of a Dominant 7 chord, B and F in this case, besides being the defining notes of the chord, also form a Tritone!

Now, let’s look at it from another angle...

These defining notes (B and F) serve as the 3rd and 7th of G7, they also serve as the 3rd and 7th degrees of Db7, only in opposite functions, now F is the 3rd and B is the 7th.

This equivalence between G7 and Db7, created by the Tritone inside these dominant chords, making these two chords switchable!

Let’s look at the next example:

We can play with these interchangeable chords in order to create 2 different variations of II-V-I cadences, you can try these equivalent progressions when reharmonizing (if it fits the melody) as well as when soloing!

The related II

Every Dominant 7 chord can be paired with its related IIm7 degree, and every dominant 7 chord leads to 2 different resolution chords. That means that we can switch up basically every component in this chord progressions, creating various interesting options for you to use.

Sub7 in the minor scale

We can use this exchange in minor chord progressions as well. In a minor II-V-I we have a half-diminished 2nd degree, a Dominant 7 5th degree, and a minor 1st degree. We can work the Sub7 here as well.

The Tritone Substitute Scale

The most simple way to approach this is to just play the original swapped scale and omit the 4th degree (which is already an avoid note).

For example, when we see a G7 → Db7, we can play the G Mixolydian scale over Db7 as well (without the C note which is the avoid note of G7).

How to really improvise over a tritone substitute...

When a chord progression consists of diatonic chords, we can easily know what scale to match every chord. When we see non-diatonic chords in the progression, it means that these unfamiliar chords have been lent from another scale.

Let’s look at this example, we can look at the Db7 chord as the 4th or 7th degree of the Melodic minor scale.

If we consider this chord as a 4th degree, we will attach the Lydian b7 scale to it, if we consider it as a 7th degree it will get the Altered scale.

☝️ Notice: When we consider a Sub7 as a 4th Melodic minor degree, the original swapped chord will serve as the 7th degree.

For example, when playing Lydian b7 over the Db, an Altered scale will work with the G7 chord. This works the other way as well, when Db gets the Altered scale, the G gets the Lydian b7 due to the fact that the Tritone divides the octave into two equal parts.

Other scales that can work over a dominant chord are the Whole-Tone scale and the Dominant Diminished scale. These two scales will work with both the G7 and its Sub7, the Db7 chord.

How to Recognise a Tritone Substitute?

It is rather simple! All you need to find are dominant 7 chords that resolve one semitone down to a tonic chord when you see this form, you can be sure that this is a Sub7 situation.

Remember, When analyzing any piece of music, it is important to first understand your harmonic surrounding (musical key) of the moment and only then inspect a specific chord function.

How to practice Tritone Substitute

In order to assimilate this technique into your playing, you need to practice both accompanying and soloing. The best way to do it is to work everything through the circle of fifths!

1. Find/build a cadence that you like according to the rules we've just learned, then work it through the whole circle of fifths.

2. Do the same with a couple of II-Sub7/V-I phrases as well. Again, write or learn by ear a few nice II-Sub7/V-I phrases and work them over the circle of fifths as well!

If you’ll do all of that, we assure you that this technique will be hard welded into your playing!

Okay fellas, this is all for now, with these new tools you will be able to finally nail those chord changes!

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