In this post, I’ll be showing you the equivalence between fifths and half steps in chord progressions.
We recently began a discussion on cyclical progressions in a previous post where I showed you how we can create predictable chord progressions by root movements in fifths.
The 2-5-1 Progression: Cyclical Progression In Fifths
Using the musical clock:
Root movements follow the musical clock counter-clockwise (in fourths)…
C to F:
F to Bb:
Bb to Eb:
Eb to Ab:
…and on and on.
One classic example of cyclical progressions in fifths is the 2-5-1 chord progression. In the key of C major, the 2-5-1 chord progression is a root movement of D:
…to G:
to C:
D to G is a downward movement of a fifth, and G to C is also a downward movement of a fifth.
Suggested reading: Nine Variations of the 2-5-1 Chord Progression.
The strongest link of the 2-5-1 chord progression is the part that moves from chord 5 to chord 1 (aka – “5-1 chord progression”), which is typically a downward movement in a fifth.
But in this post, I’ll be showing you an alternative way to move to the 1 chord.
Skeleton In The Chordboard
One of the most helpful things in chord recognition is the ability to master and remember the third and seventh (aka – “the skeleton“) of all chord qualities in all keys.
Although this may take a considerable amount of time and effort, it is worth the time and effort.
Suggested Reading: How To Play Seventh Chords With Just Two Notes.
A chord’s skeleton consists of only the most important tones. These tones are considered important because the quality of the chord depends on them.
In a 5-1 chord progression (which is the strongest link in the 2-5-1 chord progression) in the key of F major, chord 5 is the C dominant seventh:
The third and seventh tones of the C dominant seventh chord are E and Bb:
…respectively.
These tones make up the chord’s skeleton and to a large extent, are responsible for the quality of the chord being dominant. Heck, the skeleton of the C dominant seventh chord (and every other dominant seventh chord) is a diminished fifth (aka – “tritone“) interval.
The diminished interval is one of harshest intervals in music and was once considered as the devil in music because of its high degree of instability.
Unstable chords in music tend to move towards stable ones. It is the instability of the dominant seventh chord (of the fifth degree) that pulls it towards chord 1.
Summarily, the dominant seventh chord is a discord (a chord that sounds unpleasant) because its skeleton is tritonic.
Tritone Substitutions
In a 5-1 chord progression, it is possible to substitute chord 5 with another dominant seventh chord whose root is an augmented fourth lower.
The enharmonic interval of the augmented fourth interval is the diminished fifth interval we mentioned earlier as the skeleton of the dominant seventh chord.
Whether we say an “augmented fourth” or “diminished fifth” interval in music, both are related to the tritone. Check out this post on augmented fourths and diminished fifths.
Here’s a breakdown of the substitution in the key of C…
Instead of the regular 5-1 pull from the G dominant seventh chord:
…to the C major seventh:
…we’ll substitute the G dominant seventh chord with another dominant seventh chord whose root is an augmented fourth lower.
An augmented fourth below G:
…is Db:
Therefore, we’ll be substituting the G dominant seventh chord with the Db dominant seventh chord, whose root is an augmented fourth lower.
Chord substitution is the use of a chord (related or foreign) to replace another chord. The goal of chord substitution is to create a more interesting and contrasting harmony.
Simply because the augmented fourth is synonymous with the tritone, this substitution is called a tritone substitution.
A tritone substitution is the substitution of a dominant seventh chord with another chord whose root is a tritone (augmented fourth) lower.
Attention: Intervals are the building block of chords. If you’re still wondering how we got Db as an augmented fourth interval below G, then you need to subscribe to our early bird list to know when we’re releasing our latest comprehensive workbook on the study of intervals.
“Why Is It Possible To Make That Chord Substitution?”
The chord substitution we just did is possible because of the enharmonic relationship between the skeleton of G dominant seventh and Db dominant seventh.
Check it out.
Here’s the G dominant seventh chord:
…and here’s the Db dominant seventh chord:
…as well.
Using the A and B voicing concept, we can play the G dominant seventh in B voicing:
(In the B voicing of a chord, the notes are rearranged in such a way that the seventh comes before the third.)
…and the A voicing of the Db dominant seventh chord:
When both chords are played side by side with their root and fifth (G-D in the case of G dominant seventh and Db-Ab in the case of Db dominant seventh chord) removed, this leaves only their respective skeletons.
The skeleton of the G dominant seventh chord in B voicing is F-B:
…an augmented fourth.
…while the skeleton of the Db dominant seventh chord is F-Cb:
…a diminished fifth.
Treat as important… Inversion of Intervals:
All augmented fourth intervals, when inverted, become diminished fifth intervals.
Inversion of F-B which is an augmented fourth would produce B-F:
…a diminished fifth interval.
In the same vein, the inversion of F-Cb (a diminished fifth interval), would produce Cb-F:
…an augmented fourth interval.
This is the relationship between the tritone vs the augmented fourth and diminished fifth intervals.
For all intents and purposes, the F augmented fourth (F-B) and the F diminished fifth (F-Cb) are a tritone – three adjacent whole steps apart, irrespective of their harmonic role as the skeleton of the G dominant seventh chord and the Db dominant seventh chord.
F-B and F-Cb are enharmonic intervals.
Owing to the enharmonic relationship between the skeleton of G dominant seventh chord (F-B) and that of the Db dominant seventh chord (F-Cb), this substitution can hold.
Final Words
There are several reasons why we can substitute the dominant seventh chord with another dominant seventh chord and here are two of them:
Fifth and Half Step Equivalence
Cyclical progressions feature a downward movement of the root of chords in fifths.
If we put the concept of tritone substitution to work, we may not have to move in fifths, we’ll just achieve the same result by moving in half steps. Check this out…
Instead of playing “D minor seventh – G dominant seventh – C major seventh,” where the root moves in descents of fifths, we’ll have a smoother root movement in half steps from the D minor seventh:
…to Db dominant seventh:
…then to the C major seventh chord:
Using the concept of tritone substitution, we can make cyclical progressions move in half steps (D-Db-C) instead of in fifths (D-G-C) and still have the same result.
Altered Extensions
Use of the concept of tritone substitution adds the b9 and b5 tones (aka – “altered extensions”) to the basic dominant seventh chord.
Further reading: Altered Chord Voicings.
Substituting the G dominant seventh chord:
…with the Db dominant seventh chord:
…in addition to the skeleton of the Db dominant seventh chord:
…other tones – the root and fifth – are the b5:
…and the b9:
…tones of the G altered chord. We’ll go into more details in another post.
Until then.
Chuku Onyemachi
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