Substitute Dominant or “Tritone Sub” Chords

A “substitute dominant” or “tritone substitution” is a special type of chord whose function is closely related to that of the secondary dominant. So before we dive into substitute dominants, let’s review secondary dominants.

Review of Secondary Dominants

In another lesson, we talked about secondary dominant chords. This is a chord that does not belong in the home key, but belongs in a related key; namely, it is the hypothetical fifth chord from the key of whichever chord it resolves to. For instance, in the key of C major, there will be a G chord. A D⁷ does not belong in C major, but is the V⁷ of G, and so can be inserted into the key of C major before the G chord (its target destination). It’s sort of like taking a momentary step outside of the key.

What is a “Tritone Sub?”?

A tritone substitution is a chord that is substituted for a secondary dominant chord. Every secondary dominant chord can be played as a tritone substitution instead.

Let’s use the example of the V/V chord in C major. Let’s start by analyzing this chord to see what exactly gives it its “juice”.

The D⁷ introduces a new tone, F♯, which strongly wants to move up to the root of the next chord, G. The C in the D⁷ chord tends to resolve down by half step to B. The F♯ and C of the D⁷ chord are its third and seventh. So the C and the F♯ are the juice of the chord.

There is also another dominant chord that has these same two notes in it (C and F♯ ), but in this chord they are its seventh and third instead. This chord is a half step above the target, “G”. The chord A♭⁷ has A♭, C, E♭, G♭; if you spell the G♭ enharmonicIn 12-tone equal temperament, a note is enharmonic if its spelling has changed. Since G♯ and A♭ are the same note in this system, G♯ can be referred to as the enharmonic spelling of A♭.ally as F♯, you’ll see that this chord contains the same “juice” as the other dominant chord: C and F♯. In addition, its root is a half step above the root of the target, which creates a stronger bass motion:

Stop! Think for a minute!

How does your head feel? This is some pretty heavy stuff.

You must fundamentally understand secondary dominants (how they work and how they sound) before you can really understand substitute dominants, as they are an extension of this principle.

Any chord that can be preceded by a secondary dominant can also be preceded by a substitute dominant, which is a dominant chord that is one half step above the root of the destination chord. And this substitute dominant works because it shares some notes with the secondary dominant it is substituting for.

Examples

Here are a few examples of substitute dominant chords in action. Try playing through them.

Key Task

In C, name the following substitute dominant chords:

subV of I, subV of II, subV of III, subV of IV, subV of V, subV of VI

As the creator of Hub Guitar, Grey has compiled hundreds of guitar lessons, written several books, and filmed hundreds of video lessons. He teaches private lessons in his Boston studio, as well as via video chat through TakeLessons.