Tagged: harmonic progression

Reharmonizing the V7 with the SubV7

One of the most-often-used re-harmonization of the V7 is done by replacing that chord with the subV7.

Which chord is the subV7
The subV7 is a dominant chord a tritone away from the V7 (also a half step above the tonic or I)

Why does the subV7 work as a substitute of the V7?
There are two main reasons why this chord is such a perfect substitute for the V7

  • The guide tones (3 & 7) are the same in both functions.
    The 3 & 7 in the subV7 are the 7 & 3 in V7. The guide tones are the notes that give the chord its characteristic sound. In dominant chords, the guide tone (3,7) are a tritone apart. The tritone is an interval with lots of tension, [it used to be called “The devil’s interval” back in the middle ages] , which wants to resolve by moving each note half a step in opposite directions, thus turning into a major 3rd (when resolving inward) or a minor 6th (when resolving outward)
    Example: In the key of C • G7 is the V7 • 3rd is B • 7th is F (since it is a flat seventh in dominants). B-F is a tritone. It wants to resolve either: inward to C-E (major 3rd) or, outward to Bb-Gb (minor 6th). A tritone apart from G is Db which would be the root of the subV7 in the key of C, and the guide tones in Db are F (the 3rd) and C flat (the flat 7th, which is B). Thus, we can resolve those two notes, as if we were in G7, to E and C, the tritone then resolves as expected in the key of C from Db7.
  • The root of the subV7 is a half step above the I (tonic)
    The bass-line for a V7-I progression moves down a perfect fifth (which is a very powerful bass movement).
    When substituting the V7 with the subV7, the bass-line for the subV7-I is moving a half step down (which is as strong as the perfect fifth). Substituting the V7 with the subV7 gives us a strong bass-line that resolves tension well.

Here are the two examples using Mapping Tonal Harmony Pro 5 to view the different paths taken when using the V7 and/or the subV7 in the progression IIm7 – V7 – I (2-5-1)

Mapping Tonal Harmony 2-5-1 harmonic progression

The standard jazz progression (2-5-1) shown functionally in Mapping Tonal Harmony Pro

subv

The standard subV7 substitution shown functionally in Mapping Tonal Harmony Pro

The standard subV7 substitution shown in the key of Eb major in Mapping Tonal Harmony Pro

The standard subV7 substitution shown in the key of Eb major in Mapping Tonal Harmony Pro

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