Today we’re going to look at some ‘Tritone Substitutions’. So what is a Tritone and what is a Substitution?

Tritone:

A tritone is an interval, also known as an Augmented Fourth or a Diminished Fifth. It is an interval of 6 semitone’s, or 3 whole-tones. A tritone above G would be Db, so we can play a tritone by playing the open G string followed by the Db on the 6th fret of the same string.

Substitution:

What we mean by the term ‘substitution’ is that we are substituting, or swapping, one chord for another. This is a good way of spicing up your progressions by swapping in chords borrowed from a different key. You can also alter chords in the key by adding notes from outside of it. This can be a great way to add colour to a bland progression.

Tritone Substitution:

Now that we know what a tritone is and what is meant by ‘substitution’ we can look at combining them. Tritone Substitution is usually applied to a Dominant 7 chord. It can be used to create a descending bass line in a II – V – I progression. Here is an example in the key of C Major:

Original Progression (II – V – I):

In the Key of C major our II-V-I progression would include D minor 7, G dominant 7 and C Major 7.

New Progression ( II – bII – I ):

If we substitute the V chord (G Dominant 7) for a Db Dominant 7 we get a new progression.

The chords are D minor 7, Db dominant 7 and C Major 7:

As well as the V7 chord (G7 in the key of C major) the mixolydian mode works well over a bII7 chord (Flat II7). Tritone substitutions are useful for creating a descending feeling because the resulting II, bII and I chord all have their root notes a semitone apart.

The recordings below show a II, V, I followed by a II, bII, I progression. The third example has the II-V-I repeated twice followed by the II, bII, I also repeated twice. There is a melody created using the G Mixolydian Mode over the top. (Keep in mind that the bII chord is out of key and so is used mostly as a passing chord).

Footnote: The guitar used in the cover – Image by Alexander Lesnitsky from Pixabay