What is a tritone substitution in music? Well...
Tritone- The interval of an Augmented 4th or Diminished 5th.
Substitution- A stunt double for the original chord. Also, like a substitute player in a football game.
(Learn about intervals here) Tritone substitution is like an alternate route on a map. If you have your regular ii-V-I progression map, you can think of tritone substitution as an alternate route to get to the same place. These tritone substitutions deal with the melodic minor scale and the chords found within the scale. If you are confused about the melodic minor scale, review it first, before continuing. Let's start with a ii-V-I in C Major:
All of these chords are from C Major. For this original route (progression), we can create an alternate route (a tritone substitution). The tritone substitution happens with the V7 chord in a progression. We should be aware that tritone substitution is created not from G7 but from G7#11 or G7alt, so you will have to first substitute G7 for one of these other scale chords, before moving on (more on why this is later). If the melody doesn’t work with G7#11 or G7alt, stop! That means you should not use tritone substitution there. Always relate any reharmonization to the melody, because harmonization and reharmonization are like the cushions that hold the melody and give it the best possible context. If the tritone substitution can’t provide this cushion, then it’s not the right place for it, move on. So (after checking with the melody) let’s change G7 to G7#11, which comes from the D Melodic Minor scale. We can find the substitute V7 chord that we will use for the tritone substitution in the same scale a tritone away from G (which is Db). If we build a chord using the same D Melodic Minor scale (where G7#11 comes from), but starting on C# or Db (the 7th degree of the scale) we get Db7alt; a tritone substitution of G7#11. These two chords both come from D melodic minor, they are both V7 chords, and they have the same 3rd and 7th (but the roles are reversed). G7#11 has B as the 3rd and F as the 7th, and Db7alt has F as the 3rd and B as the 7th (technically written as Cb, but it’s the same note). These relationships and similarities are the reason why tritone substitutes work.
If we plug our tritone substitution into our progression, it becomes:
Dm7 and CMaj7 are from C Major. Db7alt is from D Melodic Minor.
(Bracketed notes are included in the voicings above. They might be written enharmonically, which means using a different name for the same note.) The other option we mentioned earlier is changing G7 to G7alt. This is the other available tritone substitution, which comes from Ab Melodic Minor. To find the substitute, we will repeat the same steps from the previous substitution. First, we build a chord a tritone away, on Db, now using Ab melodic minor. We get Db7#11.
If we plug our tritone substitution into our progression, it becomes:
Dm7 and CMaj7 are from C Major Db7#11 is from Ab Melodic Minor.
Tritone substitutions are possible because G7#11 and Db7alt are from the same scale, the D melodic minor scale. G7alt and Db7#11 are also related, as they come from Ab melodic minor. Unaltered dominant chords like G7 (implying Mixolydian mode of C Major) and Db7 (implying Mixolydian mode of Gb Major) are NOT tritone substitutions. They share the 3rd and 7th, but they come from different scales, so it doesn’t work as a tritone substitution. Changing The ii To further the tritone feeling, you can change the Dm7 (the ii in the ii-V-I) to the ii of the tritone substitute chord! (remember, only if it works with the melody!) So, the ii of our tritone substitute chord Db7 is Abm7, which gives us the following progressions:
Abm7 is from Gb Major. Db7#11 is from Ab Melodic Minor. CMaj7 is from C Major. Db7alt is from D Melodic Minor.
Using These Techniques Tritone substitution is a cool tool used to create chromatic bass movement and to add colour to the melody, by providing a different dominant chord cushion for it to sit on. The most important thing you should consider if you are using tritone substitution is whether the substitute chord will work with the melody! If your reharmonization doesn’t work with the melody, don’t do it! It’s like trying to draw new routes on the map that don’t exist. And if you’re drawing new routes that don’t exist, you’re just lying to yourself and screwing up the song. Now go for it and try re-harmonizing a standard using tritone subs! Do you have questions? Send me an email! tetyanahar@gmail.com
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