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Introducing Tri-tone Substitution by Tom Quayle

Hi guys and welcome to my column for this issue. Previously, we’ve been expanding our harmonic palette by studying the hugely important II-V-I progression, starting with the basic form before moving onto expanding the progression through a major key with secondary II-V-I movements. In this issue we’ll be learning another cool technique for expanding our palette even further. This technique is known as ‘Tri-Tone Substitution’ and sounds a lot more complex than it actually is.

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Before we continue, let me just re-iterate that nothing in music is like rocket science even though, at times, we may use fairly complex names for some of the concepts. Tri-tone substitution is no exception to this so don’t be afraid of the name, just take a deep breath and all will be revealed.

A tri-tone interval is exactly what it says – the musical distance of three tones. You can find a tri-tone interval on your guitar in a couple of ways. The first is to count up three tones from your starting note and since a tone is two frets this will give you a distance of six frets. The other, and more useful way, is to find your root note and simply go up a fret and up a string giving you something that looks like a flattened power chord (also known as a b5 interval).

Tri-tone substitution refers to the idea that we can take an existing V chord (a dominant 7th chord) and substitute another dominant 7th chord in its place up a tri-tone. Let’s look at an example and then I’ll explain why this works. In our basic II- V-I in C major (Dm7 – G7 – Cmaj7) we get a G7 for the V chord. If we go up a tri-tone from G we get the note C# or Db and can use a dominant 7th chord from this new note instead of the original G7. This would give us the progression Dm7 – Db7 – Cmaj7. Notice how the root movement is now going down in semitones giving a smoother sound to the progression.

The reason this works is due to the construction of dominant 7th chords. Our G7 chord contains a tri-tone interval already thanks to its F and B notes – the 7th and 3rd respectively. The Db7 chord also contains these two notes but they are now the 3rd and 7th of the chord instead. Only the root note has changed and it is this common tri-tone interval that glues the two chords together meaning that they can be exchanged with one another freely.

The tri-tone interval within both chords acts as a leading tension that resolves when followed by the Cmaj7 chord. Try it for yourself, playing each V chord starting with the G7 and then repeat the progression with the Db7 instead.

You’ll hear that both chords lead very successfully to the Cmaj7 I chord. In the video example I use a Db9 chord to add a bit of colour to the chord but you can use almost any dominant 7th chord type as long as it includes the notes B and F leading into the Cmaj7 chord. Simply use your ears as a guide.

The technique can also be with minor II-V-I progressions in exactly the same way to produce a tri-tone substituted minor II-V-I. I’ve written some examples out for you in the Tablature so you check these sounds out immediately.

We’ll deal with how to solo over these kind of progressions at a later stage, where you’ll need to develop a more intimate knowledge of dominant 7th chords and their related scales, but for now try using tri-tone substitutions in your playing and practice slowly to make it a solid part of your repertoire.

See you next time for more harmonic madness!

Good luck,

Tom

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