Harmonic Alchemy: The Eldritch Art Of Chord Substitutions

Introduction

In the previous article I introduced the idea of chordal 'mining'. This
article reveals an altogether more subtle harmonic concept, chord
'substitution'.

Substitution is a tool designed to help you find that sublime chord that can so magically transform a progression. It occurs when an existing chord within a progression is replaced by one or more of the following diatonic or non-diatonic variations:

* An Extension - where additional intervals are stacked upon a triad
e.g. Am (spelled A C E) becoming Am7 (A C E G) by stacking the b7th (G).

* An Inversion or Slash chord - where the notes of a chord are
rearranged so that the root changes to another of its intervals, e.g. Em7 (E G B D) becoming Em7/G by changing its interval structure to G B D E.

* A Polychord - where a chord is perceived as a composite of two or
more separate chords, e.g. Am13 (A C E G F#) could be viewed as an Am7 (A C E G) combined with an F#mb5 (F# A C), perhaps even a C add #11 (C E G F#).

* An alternative Voicing - where the position of the chord is changed
to produce a new intervallic structure, e.g. move an open Em (E B E G B E low to high) to the 7th position (E G B E G).

* A different Type - where a chord is changed from one type to another, e.g. Bm7 becomes B7 by sharpening its 3rd (D to D#). This approach introduces non-diatonic intervals which can be sourced from scalar variations, nearby keys or by experimenting with open ears.

* A Synonym - where chords can be given more than one name, e.g. G6 (G B D E) has the same intervals as an inverted Em7 (E G B D).

* A Passing chord - where a chord is introduced that has a
non-diatonic root, e.g. G#7 (G# D# F# C) in the key of Em. Passing chords generally share some common notes with the key (F# and C above), and in addition to straight substitutions, they can work alongside the designated subsitutee, e.g. in the progression Em G Am D7 D# dim7, where the D# diminished 7th (D# F# A C) is the passing chord and D7 was the original target. Notice the common tones F# A C between the D7 and the D#dim7.

Getting Started

In order to illustrate these concepts I have generated a basic I III IV II V diatonic progression G Bm C Am D in the relative keys of G and Em, spelled G A B C D E F# and E F# G A B C D respectively.

The chords are basic triads (G=G B D; Bm=B D F#; C=C E G; Am=A C E; D=D F# A) and below are the voices I am using.

E  3    2     0      0      2
B  3    3     1     1       3
G  0    4     0     2       2
D  0    4     2     2       0
A  2    2     3     0      
E  3
    G    Bm  C   Am    D

Extending The Chord

I am keen to give this progression a little sophistication and a mellower vibe. I find seventh chords ripe for this task, so let's extend Bm, Am and D with their diatonic sevenths. I'll leave G and C alone for the minute because uniformity is suffocating and the bane of interest. Here are the new voices,

E  2       0        2
B  3       1        1
G  2       0        2 
D  4       2        0
A  2       0
E
    Bm7  Am7  D7

Now our chord progression reads, G Bm7 C Am7 D7.

Changing The Chord Type And Passing Chords

The Bm7 (B D F# C) is a little dull for me so I am going to change its type to a B dominant 7th (B D# F# C). This introduces a non-diatonic D# note which leads satisfyingly to the upper E within the C chord.

E  2
B  4
G  2
D  4
A  2
E  
     B7

Now our progression reads, G B7 C Am7 D7.

This note has some serious theoretical pedigree. Check out the E Harmonic Minor scale. It is the Em scale with a raised seventh i.e. E F# G A B C D#. Apparently, this variation of the minor scale emerged when composers began tampering with diatonic harmony. They sought ways of making the IIIm resolve more comfortably to the Im tonic in the same way that in major keys the V major chord forms a perfect cadence with the major tonic. This was achieved
by sharpening the 3rd of the IIIm chord. This was deemed to be more harmonically pure.

The E melodic minor scale E F# G A B C# D# (raised 6th and 7th) also provides some action. Its origins are similar to the Harmonic minor but from the perspective of melody. It was decided that in ascending melodies, the raised seventh of the harmonic minor created an undesirable interval with the b6th below it (personally, I find that interval very satisfying). This was remedied by sharpening the b6th to a 6th.

Utilizing this raised 6th C#, let's replace the C with a C#m7b5 (C# B G E). This will produce a jazzier vibe which I am seeking. This chord is the first, third, fifth and seventh notes of the C Lydian mode of E Melodic Minor. Notice the C#m7b5 is simply a C maj7 with a raised root.

E
B  5
G  4 
D  5
A  4
E
     C#m7b5

The C#m7b5 is a passing chord because its root, C#, is non-diatonic to the key of G.

Now the chord progression reads: G B7 C#m7b5 Am7 D7

Similarly, if you examine the D mixolydian mode of the E Melodic Minor scale, a D# 7 #5 #9 (spelled D# G B C# F#) rears its head. Chords with altered 5ths or 9ths are commonly referred to as altered dominants. Mining scales for chords is a skill in itself, one which I may cover at a later date.

E  14
B  12
G  12
D  11
A  
E   11 
   
      D#7 #5#9

The D# 7 #5 #9 would replace the D7 nicely but instead, let's add it
alongside the D7. This sets up a neat ascending bass figure and the upper F# leads straight to the G if we repeat the progression.

Now we have: G B7 C#m7b5 Am7 D7 D#7 #5 #9

Chord Synonyms

To give the progression an even more laid back feel, let's substitute G with a G6 by adding an E to the GBD triad of the G chord.

E  0
G  0
B  0
D  0
A  2
E   3
     G6

Also, let's make the D# 7 #5 #9 the turnaround point and repeat the
progression. The second time through though, let's substitute the G6 with an Em7 to create an interesting chromatic bass line between the D7, D#7#5#9 and Em7 chords. Note the G6 chord (G B D E) and the Em (E G B D) have the same notes although their interval structure is different. With chord synonyms you must think literally i.e. the word is different but the meaning the same.

E  0
B  3
G  0
D  0
A  2
E  0
    Em7

Now we have: G6 B7 C#m7b5 Am7 D7 D#7 #5 #9 | Em7 B7 C#m7b5 Am7 D7 D#7 #5 #9

Changing The Chord Type

Instead of using the D# altered dominant twice and ruining its unique flavour, lets substitute the first one with a D# diminished 7th. D# dim7 (D# F# A C) comes from the mixolydian mode of the E Harmonic minor scale.

E
B  7
G  5 
D  7
A  6
E  
     D# dim7

Similarly, lets not overdo the C#m7b5 and put the original C back in the first time.

This leaves us with: G6 B7 C Am7 D7 D# dim7 | Em7 B7 C#m7b5 Am7 D7 D#7 #5 #9

Now for another extension. Let's replace the Am7 second time with an Am13. The 13th is an F# so its diatonic (not that it matters!). Notice how the upper F# returns in the D7 that follows, adding some pleasant continuity.

E   5
B   7
G   5
D   5
A   7
E    5
      Am13

Polychords

The Am13 (A C E G F#) can be seen as a composite of Am7 (A C E G) and an F#mb5 add b9 (F# A C G). This illustrates the concept of the polychord, where one chord can be perceived as two or more separate chords. With this in mind lets replace the second Am13 with the F#mb5 add b9.

E   3
B   1
G   2
D
A
E    2
      F#mb5 add b9

Now we have, G6 B7 C Am13 D7 D# dim7 | Em7 B7 C#m7b5 F#mb5 add b9 D7 D#7 #5 #9

Chord Voices

Finally, to vary the dynamic of the bass line, lets change the voice of the Em7 to this variation,

E  3
B  3
G  4
D  2
A
E
    Em7

Experimenting With Open Ears

On a whim, I have decided to substitute the first C with a Csus4. I like the way the F creates a descending chromatic line in the 5ths of the B7, Csus4 and Am7 chords.

E  1
B  1
G  0
D  3
A  3
E
    C sus4

It has a non-diatonic F which can't be explained by the Harmonic or Melodic minor scales. Actually, I borrowed this chord from the key of C, a close neighbour.

The progression is now as follows, G6 B7 Csus4 Am13 D7 D# dim7 | Em7 B7 C#m7b5 F#mb5 add b9 D7 D#7 #5 #9

Common Notes And Neighbouring Keys

Now let's substitute the penultimate D7 with a an G#7 (G# D# F# C). The D# note popped up earlier in the E harmonic minor scale. The G# note introduces some fresh air, and like the F in the Csus4 chord earlier, this note was borrowed from the key of C (or the A harmonic Minor scale to be precise). In addition, the G#7 shares two common notes ( F# and C) with the D7 and makes for a slick change to the D#7 #5#9 chord.

E   11
B   13
G   11
D   13
A   11
E    
      G#7

Here is the updated progression, G6 B7 Csus4 Am13 D7 D# dim7 | Em7 B7 C#m7b5 F#mb5 add b9 G#7 D#7 #5 #9

Now let's close it down with a plain Em played in the 12th position.
Sometimes less is more...

E  12
B  12
G  12
D  14
A  14
E  12
      Em

The final progression is now: G6 B7 Csus4 Am13 D7 D# dim7 | Em7 B7 C#m7b5 F#mb5 add b9 G#7 D#7 #5 #9 Em

Bear in mind that we started with G Bm7 C Am D7.

Conclusion

This article has only really scratched the surface but I hope it gave you an insight into the substitution underworld and enhanced your appreciation of chordal harmony.

You may have wondered about some of the decisions I took. How did I know that a certain substitution would give me a desired effect for example? This is simply down to individual taste, imagination and experience. Harmonic explorations bring you closer to your chords. They get you thinking about the component notes of chords and the complex relationships between them.

This deeper understanding will in turn benefit your soloing, because better appreciating what happens below can only improve your melodies above.

Further research is required so here are some study tips:

1) Practice the chord scale of every key. The more familiar you are
with the diatonic chords, the easier you will be able to deal in passing chords. This is not as daunting as it sounds because the order of chord types is always constant from key to key.

2) Analyze chord progressions to identify the modal source of each
chord.

3) Make a note of the similarities between different keys. This will
help you spot key changes.

4) Remember to use your ear at all times. Sometimes there is no obvious theoretical reason why something works. This should not concern you if it sounds good. This is the most valid reason of all to run with an idea. After a heavy substitution session, return to the progression your original progression and decide whether you have actually improved it.

5) Don't write by numbers. Let the essence of the theory sink in and
then set your imagination free to wander.

Guy Pople is a music, education and multimedia specialist based in the UK`s North-West. He plays guitars, studies theory and runs St Annes Music in Lytham St. Annes, a one-stop shop for musicians on the Fylde coast of Lancashire. St Annes Music offers professional instruments, recording, tuition and accessories.

His live band Nomad is currently building up their original music. You can catch him
on Virtual Strangers.

Guy Pople

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