MinorScales
When we say "Minor Scale", we usually mean the Aeolian scale which is the same as a Major scale starting with its 6th note. But a Minor scale often changes its form to create harmonic or melodic momentum. It can yield two variations of itself, called a Harmonic Minor scale and a Melodic Minor scale respectively. Sometimes, we call the original Minor scale the "Natural Minor scale" in order to highlight that the scale is in its unaltered form.
Let's take the A Minor Scale and see what its variations look like. First, there's the A Harmonic Minor scale. This scale differs from the A Natural Minor by one note - G# vs G. The 7th note in the Natural Minor scale gets raised by a half step to create the Harmonic Minor scale. This is done in order to meet the harmonic change introduced by the V (five) chord of the key. In minor keys, you can change the Vm (five minor) chord into V, in order to increase the harmonic momentum towards I (one). V has a stronger inclination towards I than Vm does. (The same can be said about V7 vs Vm7.) And when you change the chord, you'll also want to modify the scale accordingly. This is how you come up with the Harmonic Minor. Changing the Natural Minor into the Harmonic Minor is like borrowing the 7th note from the Major scale with the same root (the parallel Major scale - the A Major in this case). The 7th note of a major scale is called the "leading tone", and it has a strong inclination towards the root (the 1st note) which is a half step above it.
Next, we have the A Melodic Minor scale. It differs from the A Natural minor by two notes - F# vs F and G# vs G. The 6th and the 7th notes in the Natural Minor get raised by a half step to create the Melodic Minor scale. As the name suggests, this is done for a melodic reason. I mentioned that the raised 7th note in the Harmonic Minor scale has a stronger momentum towards the root than the original 7th note in the Natural Minor. So it makes sense you want to raise the note when you go up the Minor scale towards the root. But if you raise it, then the gap between the 6th note and the 7th note becomes wide: The interval is an augmented second, or three semitones. This is why you'll want to raise the 6th note as well, to even out the intervals and make the linear movement smoother. You can also go down the Melodic Minor scale from the root. Strictly speaking (and I think this is more of a traditional point of view), the Melodic Minor has two forms - the ascending form and the descending form. The descending form of the Melodic Minor, which can be used when going down the scale, is exactly the same as the Natural Minor. But, personally, I think it's okay to use the ascending form (the figure with the two raised notes) for both going up and down.
Let's take a chord sequence of Am-E7-Am. The A Natural Minor scale works on the two Am chords, but when the chord moves to E7, the chord presents one note that's not included in the Natural Minor - G#. Therefore you need to modify the scale to make it match the contents of the E7 chord. Here, you have two choices - the A Harmonic Minor or the A Melodic Minor. Both can work because they contain G# and all the other notes in E7, namely E, B and D.
Let's see another chord sequence. What if it's Am-E7(b9)-Am? Now, your only choice for the E7(b9) will be the A Harmonic Minor. The notes in E7(b9) are E, G#, B, D and F, therefore you can't use the Melodic Minor which contains F#. Likewise, if the sequence is Am-E9-Am, your only option for the E9 will be the A Melodic Minor. E9 contains E, G#, B, D and F#, so you can't use the Harmonic Minor which contains F.
By the way, if you choose to address those minor scales from the stand point of the V, you'll get different names. The A Natural Minor will be called the E Phrygian, the A Harmonic Minor will be called the E Phrygian Dominant, and the A Melodic Minor will be called the E Mixolydian b6. (See the "V7 Possibilities" entry.)
To conclude this entry, when you see a V chord (instead of Vm) in a minor key, you can assume that the appropriate minor scale at that moment is the Harmonic Minor unless you see one or both of the following, in which case the Melodic Minor is appropriate:
?The V is a chord that includes the tension 9, like E9.
?The melody implies the Melodic Minor by presenting both the raised 6th and the raised 7th.
Examples of "the melody implying the Melodic Minor" can be seen in tunes such as Autumn Leaves (Kosma), Greensleeves (English traditional), I Hear a Rhapsody (Fragos, Baker, Gasparre), Lullaby of Birdland (Shearing), Nature Boy (Ahbez) and Yesterday (McCartney)
Scales-Minor-Scales関連ページ
- Guitar: Diatonic Scale Positions
- Electronic Musician
- Scales: Diatonic Scales
- Electronic Musician