Major vs Minor
The defining difference between a major scale and minor scale is the interval between the 1st and 3rd degrees. As you probably know a major third is made up of two whole tones, while a minor third is a whole tone and half tone.
With minor harmony we can build diatonic chords on each degree of any of the minor scales or modes, just as we can with the major scale. Here is an example using the dorian mode.
But it’s a bit more complicated because with minor tunes there isn’t just one basic scale to use for creating the bait chords. You will remember from the chapter on Modes that the Dorian, Phrygian and Aeolian modes are all minor scales, i.e. the interval between the root and 3rd degree is a minor third.
Out of these modes, the Aeolian mode is probably the most common. Note that in this mode the chords on I, IV and V are all minor. (Ex: 6c)
The aeolian mode (sometimes referred to as the natural minor) is often what we mean when we say a tune is in a minor key. As we mentioned previously the aeolian is the relative minor of the major key which uses the same key signature, so A minor (aeolian) is the relative minor of C major.
But we also have the harmonic minor scale which is very similar. The one big difference is thatt the 7th degree is raised a semitone to provide a leading note, i.e. a semitone leading from the 7th to 8th degree of the scale, which supplies a satisfying perfect cadence:
We can see in ex 6d how the raised 7th in the harmonic minor allows for a “conventional” V-I cadence, where the V chord is a dominant 7th rather than a minor 7th.
To really understand this you should play it on a keyboard to listen for the differences between the modal and leading note cadence.
If the harmonic minor scale is used melodically the augmented second interval between the 6th and 7th creates an exotic middle eastern sort of flavour.
This is not the case with the melodic minor as it also has a raised 6th which makes it a closer relation to the Dorian mode. (ex 6e). In jazz this scale is used both ascending and descending.
To understand “tonal” (non modal) minor harmony we need to build chords on the scales as we did with the major scale in ex 1b.
Note that there are two possibilities for the root of the VI chord, depending on whether the harmonic or melodic scale is used.
So is minor harmony really this complicated?
Apart from the fact that this is rather complex, there are some other things to think about here. The alterations to the 6th and 7th degrees of the scales were made for melodic not harmonic considerations. Using these scales to create chords is unsatisfactory in some cases, so in practice alternatives are “borrowed” from modal harmony, usually the Dorian or Aeolian:
- Chord I. The major 7th is fine in some cases but the leading note is harmonically unnecessary and can sound slightly dissonant or too sophisticated for certain styles. It also clashes unpleasantly if there is a tonic in the melody. Other chords that can be used for chord I in a minor key are Im (triad), Im6 (from Dorian or melodic) or Im7 (from Dorian) – see ex 6h.
- Chord II. The harmonic version (half diminished) is usually more satisfactory.
- Chord III. The leading note (B natural) is ungainly and unnecessary as the chord is rarely if ever used as a chord in a cadence. A Bb (Dorian or Aeolian) is usually better.
- Chord IV. Either chord is suitable. The m7 gives more of a minor flavour, but the dominant 7th on the IV is common, especially in latin jazz or funk sequences with 2 chords repeated, e.g. Cmin7/F7/.
- Chord V. Raised 7th is good as it allows for the conventional V7-I cadence.
- Chord VI. Either chord can be used, depending on the preceding or following chords.
- Chord VII. Could be either but the one built on the leading note (diminished) is more common. The VII chord is sometimes used as an alternative to a V7 chord and the diminished 7th makes a more satisfactory cadence.
Although this appears more complex than major harmony it allows for a great deal of variety. To simplify we could use a combination of chords based on harmonic minor harmony with some “borrowed” modal chords.
As mentioned above there are several possibilities for tonic chords in a minor key (ex 6h).
Note that in a m6 chord the added 6th is always a major 6th. In jazz earlier than the 60s a minor 7 is rarely used as a tonic minor and should be not be used to avoid confusion with IIm7.
Melodic and stylistic considerations need to be taken into account when choosing which type of tonic minor chord to use. (Eg. m maj7 and m6 may sound too sophisticated or too old-fashioned in some styles). When using RN analysis a minor triad, m6 or m maj7 often indicate a minor tonic, – useful for locating new key centres. (m6 or minor triad could be chord IV, of a minor key, but if so this will be obvious by the presence of a minor tonic nearby)
It is important to show which root the VI and VII chords are based on when doing an RN analysis in a minor key:
|VI chord whose root is a minor sixth above the tonic
|VI chord whose root is a major sixth above the tonic
|VII chord whose root is a minor seventh above the tonic
|VII chord whose root is a major seventh above the tonic