There are two primary ways for a guitar player to incorporate a non-diatonic chord into a progression.
A non-diatonic chord can substitute for another chord or function as a passing chord, one used to create a smooth transition between two other chords.
This post will:
- Cover the most common types of non-diatonic chord substitution, providing examples for each one.
- Cover the most common methods of inserting a passing chord into a progression, providing examples for each one.
Non-diatonic Chord Substitution
A non-diatonic chord substitution is one in which a non-diatonic chord — one not from the harmonized scale of the key center — is substituted for another chord in a progression.
Two of the most common types of non-diatonic chord substitution are:
- The tritone substitution (or flat five substitution).
- The vii°7 for V7 substitution.
Tritone (or Flat Five) Substitution
A tritone substitution is when a functioning dominant seventh chord is replaced with the dominant seventh chord whose root note is a diminished fifth away.
Example #1
The progression in fig.1 is in the key of G major and includes a functioning dominant seventh chord (D7) that resolves to the tonic chord a perfect fifth below it (G major).
Fig.1
A tritone substitution would involve replacing the D7 chord with an Ab7 chord, the dominant seventh chord whose root note is a diminished fifth away.
The progression in fig.2 includes the Ab7 for D7 tritone substitution.
Fig.2
A tritone substitution accomplishes two things:
- It creates a descending, chromatic bass line (A – Ab – G), which makes for a smooth transition between the chords.
- It allows for the same sense of resolution when the substituted bII7 chord moves to the tonic chord a half step below it.
Example #2
A tritone substitution can be applied to any functioning dominant chord, including a secondary dominant chord.
The progression in fig.3 is in the key of D major and includes a functioning, secondary dominant chord (B7) that resolves to the chord a perfect fifth below it (Em).
Fig.3
A tritone substitution would involve replacing the B7 chord with an F7 chord, the dominant seventh chord whose root note is a diminished fifth away.
The progression in fig.4 includes the F7 for B7 tritone substitution.
Fig.4
The vii°7 for V7 Substitution
A vii°7 for V7 substitution is when a functioning dominant seventh chord (the V7 chord) in a major key chord progression is replaced with the diminished seventh chord built on the seventh degree of the same major scale (the vii°7 chord).
Example #1
The progression in fig.5 is in the key of C major and contains a functioning dominant seventh chord (G7) that resolves to the tonic I chord a perfect fifth below it (C major).
Fig.5
A vii°7 for V7 substitution would involve replacing the G7 in the progression with a B°7, the diminished seventh chord built on the seventh degree of a C major scale.
The progression in fig.6 includes the B°7 for G7 substitution.
Fig.6
A vii°7 for V7 substitution accomplishes two things:
- It adds some color and variety to the progression, creating a slightly different sound.
- It allows for the same sense of resolution when the substituted vii°7 chord moves to the tonic chord a half step above it.
Example #2
A vii°7 for V7 substitution can be applied to any functioning dominant chord, including a secondary dominant chord.
The progression in fig.7 is the same one shown in fig.4 above. It is in the key of D major and includes a functioning, secondary dominant chord (B7) that resolves to the chord a perfect fifth below it (Em).
Fig.7
A vii°7 for V7 substitution would involve replacing the B7 (the V7 chord in the key of E major) in the progression with a D#°7, the diminished seventh chord built on the seventh degree of an E major scale.
The progression in fig.8 includes the D#°7 for B7 substitution.
Fig.8
Passing Chords
A passing chord is a non-diatonic chord — played between two other chords — to create a smoother transition between them.
Dominant Seventh Passing Chords
A non-diatonic, dominant seventh chord is commonly used as a passing chord.
Three approaches are detailed below.
Half Step Dominant Seventh Passing Chords
One approach is to precede a chord in a progression with the dominant seventh chord whose root note is located a half step above or below it.
For example, if a chord progression contains a Bm chord, it could be preceded by:
- A Bb7 chord.
- A C7 chord.
The progression in fig.9 is in the key of G major and contains a Bm chord.
Fig.9
Fig.10 shows the same chord progression but with a Bb7 passing chord, immediately preceding the Bm chord.
Fig.10
Secondary Dominant Passing Chords
Another approach is to precede a chord in a progression (other than the tonic chord) with its own V7 chord, the dominant seventh chord whose root note is located a perfect fifth above it.
For example, if a chord progression contains a Gm7 chord, it could be preceded by a D7 chord, the dominant seventh chord whose root note is located a perfect fifth above it.
The progression in fig.11 is in the key of Bb major and contains a Gm7 chord.
Fig.11
Fig.12 shows the same chord progression but with a D7 passing chord, immediately preceding the Gm7 chord.
Fig.12
bV Passing Chords
A third approach is to precede a chord in a progression with the dominant seventh chord whose root note is located a diminished fifth away.
For example, if a chord progression contains an E7 chord, it could be preceded by a Bb7 chord, the dominant seventh chord whose root note is located a diminished fifth away..
The progression in fig.13 is in the key of G major and contains an E7 chord.
Fig.13
Fig.14 shows the same chord progression but with a Bb7 passing chord, immediately preceding the E7 chord.
Fig.14
Diminished Seventh Passing Chords
A non-diatonic diminished seventh chord is also commonly used as a passing chord.
Two approaches are detailed below.
Half-step Diminished Seventh Passing Chords
One approach is to precede a chord in a progression with the diminished seventh chord whose root note is located a half step below it.
For example, if a chord progression contains an A7 chord, it could be preceded by an Ab°7 chord, the diminished seventh chord whose root note is located a half step below it.
The progression in fig.15 is in the key of D major and contains an A7 chord.
Fig.15
Fig.16 shows the same chord progression but with an Ab°7 passing chord, immediately preceding the A7 chord.
Fig.16
Same-root-note Diminished Seventh Passing Chords
Another approach is to precede a chord in a progression with the diminished seventh chord whose root note is the same as the root note of the chord it precedes.
For example, if a chord progression contains a C7 chord, it could be preceded by a C°7 chord, the diminished seventh chord whose root note is the same as the root note of the chord it precedes.
The progression in fig.17 is in the key of F major and contains a C7 chord.
Fig.17
The same chord progression is shown in fig.18 but with a C°7 passing chord, immediately preceding the C7 chord.
Fig.18
Half-step Same Quality Passing Chords
Any chord in a progression can be preceded by the same quality chord whose root note is located a half step below it.
For example, if a chord progression contains a C#m7 chord, it could be preceded by a Cm7 chord, the same quality chord (minor seventh) whose root note is located a half step below it. .
The progression in fig.19 is in the key of B major contains a C#m7 chord.
Fig.19
Fig.20 shows the same chord progression but with a Cm7 passing chord, immediately preceding the C#m7 chord.
Fig.20
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