How to Play Jazz - Tritone Substitution Explained

Tritone Substitution is a form of reharmonization, used often by jazz musicians to spice up their sound when playing old jazz songs from the past.

'Tritone' is a term used to describe the augmented 4th/diminished 5th interval. For example, the interval between C and F# is a tritone.

The tritone interval is found in several types of chord, but it features most prominently in the dominant 7 chord (C dominant 7 is C E G Bb).
The tritone in this chord is found between the major 3rd (E) and the flat 7 (Bb).

Here's the cool part:
E and Bb are also the tritone of another dominant 7 chord, other than C dominant 7. F# dominant 7 also has an E and a Bb in it: F# A#(Bb) C# E. In F# dominant 7, E is the flat 7, and Bb is the major 3rd (correctly spelled A#).

This means that whenever you see a C dominant 7 chord symbol, you can substitute it for an F# dominant 7 instead. In doing this, you keep the important tritone sound, while also creating a new and more sophisticated slant in the harmony.

So every time you see a dominant 7 chord symbol, try substituting it for the dominant 7 chord a tritone away (up or down). E.g. if you see a Bb dominant 7, play E dominant 7. If you see a G# dominant 7, play D dominant 7.

When you apply this to ii-V-I progressions, you will notice that you get a nice chromatic moving bassline (moving by half step downwards). For example, in C major:
The ii chord will be D minor
We can tritone substitute the V7 chord, G dominant 7, becomes Db dominant 7.
The I chord is C major.

Try playing:
D minor 7 (D F A C), Db dominant 7 (Db F Ab Cb), C major 7 (C E G B).

Sounds pretty cool doesn't it!

Sometimes you will have to alter some of the melody notes slightly, to fit with the new chord symbol. Say the original dominant 7 chord was G dominant 7, and the melody note was an A natural. If you substituted the G dominant 7 for the same chord a tritone away, Db dominant 7, then the A natural would become dissonant when played over the new chord. So you would have to alter the A natural, and make it an Ab or maybe a Bb. Whatever sounds good to you.