Harmonic function in minor keys – the tonic

At long last I’m going to continue my exploration of minor keys. In the first post in this series I observed that attempting harmonic analysis of music written in minor keys is difficult. The rules that work so well for major keys don’t seem to work well at all when applied to minor keys.

However, one thing that seems clear to me is that functional harmony must still play a part. Regardless of whether a piece is written in a major or minor key we still need to create a sense of forward motion.

The problem with scales

Many sources of information on the subject of minor key harmony start by looking at the major scale and the relative minor (also known as the Natural Minor, or Aeolian mode).

The first step is usually to harmonise the relative minor using the same rules we apply to the major scale. When you do this you end up with a very unsatisfactory V chord; a minor 7. The minor 7 chord contains no tritone – like that between the 3 and 7 found in a dominant 7 chord – to provide intervalic tension that needs to be resolved. As such the minor 7 chord provides no forward motion.

Here’s an example of a harmonised minor scale (A minor, the relative minor of C major).

You can see the V cord is a minor 7.

Typically, the solution to the unsatisfactory V chord is seen as using starting with a different scale. Rather than using the Natural Minor the approach is to use the Harmonic Minor instead, essentially following the classical tradition. Recall that the Harmonic Minor scale is the same as the Natural Minor with one exception; the b7 is raised to a 7. This change affects four of the chords in the harmonised scale, including the V chord which now becomes a dominant 7 (V7).

Interestingly though, authors such as Mark Levine don’t deal with the Harmonic Minor scale. They start by looking at the Melodic Minor scale instead. Like the Harmonic Minor scale, the Melodic Minor has the major seventh (7) but it also has a flattened third (b3). In The Jazz Theory Book, Mark Levine devotes a chapter to the Melodic Minor scale but nothing to the Harmonic Minor.

Chord functions instead of scales

The authors of The Berklee Book of Jazz Harmony helpfully devote a chapter to minor key harmony but take an approach that focuses on chord functions rather than on minor scales.

As I understand it, the justification for this approach is that for any given tune written in a minor key there are a number of candidate minor scales that can be used as the source scale (e.g. Natural, Harmonic and Melodic Minor as well as Dorian and Phrygian). However, jazz tunes are not usually that straightforward and are rarely diatonic to any one scale.

Most musicians are familiar with the natural, harmonic, and melodic minor scales as well as two additional tonic minor modes: Dorian and Phrygian… Minor key jazz tunes are rarely diatonic to just one of these scales. Typically, chords from several of these sources are used interchangeably.1

An alternative approach is to identify how chords are being used in terms of their harmonic function within the tune. You can then figure out what source scales can be used to derive each chord on a case by case basis. This approach looks at harmonic function first and reverse engineers the related scales (the modal source) for each chord function.

For the remainder of this and other posts on the subject I’ll be looking at the Berklee approach in more detail, starting with the tonic function.

Tonic chords in minor keys

All music needs a tonal centre; the tonic. Where do the tonic chords in minor key tunes come from? The Berklee book states the following:

In minor key music, the tonic chords usually come from the melodic minor or Dorian, although Aeolian or Phrygian are possibilities as well.2

The above quote is really important. It identifies four possible source scales for Tonic function chords:

  • Melodic minor
  • Dorian
  • Aeolian
  • Phrygian

Notice Harmonic Minor isn’t one of them! Let’s look at each in turn.

Melodic Minor

The melodic minor scale yields two primary tonic chords:

  • I-6
  • I-(Maj)7

Note: Unlike the major key (Ionian mode) which has an avoid note on the 4th degree of the scale, there are no avoid notes in melodic minor.

There are also 2 other possible members of the minor key tonic group:

  • VI-7b5
  • bIII+(Maj7)

Dorian

The Dorian mode is the source for the I-7 chord as well as being an alternative source to melodic minor for the I-6. The 9, 11 and 13 tensions are all available. The Berklee book talks about Dorian source scales being harmonised with quartal chord voicings but I won’t go in to that here.3

Aeolian

Aeolian gives us two potential tonic chords:

  • I-7
  • bIIIMaj7

Aeolian as a source scale leads to a darker sound. Remember that the b6 of the Aeolian scale is an avoid note. The bIIIMaj7 has common tones with the I- and can be used to cause a tonal shift to the relative major key.

Phrygian

The Phrygian mode is used infrequently as the source for tonic chords. However, the Berklee book refers to I- being used with quartal voicings.

Summary

Now, I’ve skipped a ton of detail above but the Berklee book summarises the tonic function in minor keys as follows:

Tonic chord Source Scale Chord Scale
I-6
I-(Maj7)
Melodic Minor Melodic Minor
VI-7b5 Melodic Minor Aeolian b5 (Locrian Natural 9)
bIII+(Maj7) Melodic Minor Lydian Augmented
I-7
I-6
Dorian Dorian
I-7 Phrygian Phrygian
I-7 Aeolian Aeolian
bIIIMaj7 Aeolian Ionian

References

  1. Mulholland & Hojnacki (2013). The Berklee Book of Jazz Harmony, p.83
  2. Mulholland & Hojnacki (2013). The Berklee Book of Jazz Harmony, p.84
  3. Mulholland & Hojnacki (2013). The Berklee Book of Jazz Harmony, p.87

 

 

 

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