tritone substitution origins

7/30/2019 Tritone Substitution Origins

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In its most common application, tritone substitution refers to the replacement of one dominant

chord with a second dominant chord with its root a tritone away. For example, the replacement of

a G7 chord with a Db7 chord. Very often, the tritone sub will be used when the dominant chord

in question is resolving to a tonic chord (C major in the previous example), although this is not

always the case. There are many other types of tritone substitutions, but this is the most basic and

common usage. During our study of tritone subs, we will get into the reasons why they work, andhow jazz musicians have used them both in composition and improvisation.

While not immediately applicable to our study of tritone substitutions, I thought it would be fun

to begin by looking at the origins of this sound. There are two types of chords used in harmonic

progressions by composers especially of the Classical and Romantic periods, to which the sound

of the tritone substitution can be attributed. While they do not technically function as the tritone

sub that I described in the previous paragraph, you can see and hear the similarities.

The first of these chords is known as the

Neapolitan 6th. Lets look at how this chord isderived through the movement of one melodic

voice. Start with a simple iv-V-i progression in

c minor. So, Fm-G-Cm (figure 1). In root

position, the iv chord has the C in the highest

voice. By moving the C up a half step, you

can change that chord to a Db major chord in

first inversion (figure 2). This is called a

Neapolitan 6th chord, because chords in first

inversion are referred to as 6th chords. This

has to do with the intervallic relationship of a6th between the bottom note (in this case F),

and the top note (in this case Db). We now

have a progression that looks like this: Db/F-

G-Cm. You will notice that the Db/F chord

functions as a predominant chord going to the

dominant chord (G), then finally resolving to

the tonic chord (Cm).

Remember the tritone sub from the first paragraph? G vs. Db. Although a Neapolitan 6th chord

does not replace a dominant chord, as in a tritone sub, it does have that special sound that we can

relate to the sound of a tritone sub. This is due to the fact that it is a chord whose root is a half

step away from the tonic (Db to C).

The second type of chord that can be considered a forerunner to the tritone substitution is called

an Augmented 6th chord. This chord can also be derived from a basic chord progression where

the movement of one melodic voice can create the change of sound. This time, start with the

following progression: iv6-V-i in c minor. So, Fm/Ab-G-Cm (figure 3). Youll notice that we


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have a iv chord in first inversion to begin

with this time, so its almost the same

progression that we started with when

discussing the Neapolitan 6th chord. Again,

lets focus on the first chord in the

progression. In first inversion, this chord hasthe F in a higher voice. By moving the F up a

half step, we get an F# which creates the

interval of an augmented 6th with the Ab in

the bass (figure 4). This incomplete chord is

called an Augmented 6th chord, or more

specifically, an Italian +6 chord. If we spell it

from the bottom up, and use the enharmonic

equivalent of F#, which is Gb, youll notice

that we are looking at an Ab7 chord without a

5th. Try playing it on the piano: youll hearthat it sounds like a dominant chord. In fact,

the chord 5th can be omitted from many

chords without changing the basic sound.

Looking at the context of the Italian +6 chord

in modern-day terms, you have a progression that is essentially Ab7-G-Cm.

So wheres the tritone substitution? This time we are observing the relationship between the first

and second chords, Ab7 and G. Youll notice again the same half step relationship between the

roots of the chords that we had before with Db and C. This is the telltale sign of a potential

tritone substitution! Working backwards, check to see if Ab would be a tritone sub of the

dominantof G. Well, the note a tritone away from Ab is D, and since D is the dominant chord inrelation to G, then Ab would be the tritone sub. In this case, it just happens to be a dominant of a

dominant which we call asecondary dominant. Confusing, I know! But the point is that you can

have tritone substitutions in many different situations, although they usually function as

dominant chords of some sort.

There are two more special types of Augmented 6th

chords besides the Italian +6. These are the German +6

and the French +6. Both share the three tones which make

up the Italian +6 chord. The German +6 chord (figure 5)

adds the diatonic minor third scale degree and the French

+6 chord (figure 6) adds the diatonic second scale degree.

Keep in mind that these are the scale degrees of the key of

the progression, not the root of the chord. So in our

progression from before, the minor third would be an Eb

and the second would be a D. The German +6 chord, if

looked at from a modern standpoint, would be a complete


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dominant 7th chord. The French +6 chord could then be

viewed as a dominant 7th chord with a flatted 5th. We see

this type of chord all the time in jazz!

Because the German and French augmented 6th chords

share the same basic tones as the Italian +6 chord, theyhave the same harmonic function with just a subtle

change of color.

The reason why both Neapolitan 6th chords and Augmented 6th chords are shown in minor keys

is because that is where they were born. This does not mean that they cannot occur in major

keys, although some pitches have to be borrowedfrom the minor key in order for these sounds to

occur. In the previous examples, we used minor iv chords and changed one note in order to attain

the new types of chords. In order for this to work in a major key, we would have to borrow the

Ab from the minor key instead of using the A that is already present in the major IV chord.

Likewise, we would have to borrow an Eb if we chose to use the German +6 chord, because itrequires that pitch in order sound the way it does. In jazz we dont really think about borrowing

from minor keys if we are in a major key, because it happens so often! Think about the 7th

measure of Cherokee. The tune is in concert Bb major and the chord in measure 7 is an Eb

minor chord. Eb minor is a borrowed chord from Bb minor, because it wouldnt naturally exist in

the key of Bb major.

Finally, I would suggest playing through all of the examples on the piano (slowly is fine!) to get

an idea of how these chords function. These sounds are probably already familiar to you even if

you never knew what to call them, or how they worked.

tritone substitution origins

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