The tritone substitution is a staple of jazz guitar that’s been used by the greats. Here’s how you can use it to quite literally jazz up your chord progressions

The term tritone refers to an interval that spans three whole tones. For example, this could be: C to D, D to E then E to F#. However, another way of looking at it could be as an augmented 4th (C to F#) or a diminished 5th (C to Gb). As you can see, these are all different names for one specific sound. 

Once we get into chord progressions and ‘diatonic speak’ such as II-V-I, you may well come across the term ‘tritone substitution’. All this actually means is that a chord within a progression (usually the V) has been exchanged for another with the root a tritone away.

Let’s explore this with a couple of examples. First, a jazzy II-V-I in C major would be Dm7-G7-Cmaj7. Then, if we move the G7 up a tritone/aug 4th/dim 5th, we will get a Db7. Now, the progression would be Dm7‑Db7-Cmaj7, which can support many of the same melodic ideas but positions them in a different light. Why not get experimental and have a go at a Dm7‑Dbmaj7-Cmaj7 progession?  

Example 1. Em9

If we took an Em-A7-D (II-V-I) progression and decided to jazz it up with 7ths and extensions, we might well start with this Em9 chord. The F# (9th) is our highest note. I mention this because the F# will be the highest note of one of our other examples, too.

Example 2. Eb9

As the V chord, the A is the most likely candidate in our sights for substitution. Let’s make it a dominant 7th, then shift it up a tritone (#4/b5) to give us Eb7. Then let’s go even further and make it a Eb9. Now we’re ready for the I chord.

Example 3. Dmaj9

The I of our II-V-I (D) sounds a bit plain after all that, so I’m opting to make it a Dmaj9. This voicing with the E (9th) on top gives a chromatic run down in parallel with the bass, which sounds harmonically linear and pleasing – though, as always, it’s a personal choice

Example 4. Eb7#9

Now we’ve heard the ‘deluxe’ version of the II-V-I, let’s have a play with some alterations. How about this Eb7#9 in place of the Eb9? It keeps the F# from our Em9 as the highest note, which gives a nice continuity as the other voices shift. Follow with a Dmaj7 with the F# on top and you have a matching set!

Example 5. Ebmaj7

This final example goes slightly outside the theoretical definition of a tritone substitute by being a major 7th rather than dominant 7th, but I don’t think we should let that bother us as it sounds great! This Ebmaj7 fits beautifully if you finish by playing the same chord down one semitone/fret to finish on Dmaj7.