HARMONIC AND MELODIC MINOR SCALES
Problem with natural minor scale
The problem with a natural minor scale is that its seventh scale degree does not lead particularly well to the tonic because the distance between them is the major second. We have learned before that, in such a case, the seventh scale degree is called the subtonic.
We also know that there is no such a problem in major scales. In a major scale, the seventh scale degree leads well to the tonic because the distance between them is the minor second. This is the reason why, in such a case, the seventh scale degree is called the leading-tone.
To create successful melodies and harmonies, oriented around the tonic, it is important that the seventh scale degree leads well to the tonic.
Harmonic minor scales
To solve the problem with the seventh scale degree in the natural minor scale, the seventh scale degree is raised. This is often enough for making successful harmonies. This is the reason why the resulting scale is called a harmonic minor scale. The next figure shows the A harmonic minor scale.
Figure: The A harmonic minor scale
The structure of harmonic minor scales is defined by the list of the seconds: M2, m2, M2, M2, m2, A2 and m2. The last minor second leads us to the tonic again, only now it is one octave higher. We see that harmonic minor scales have the leading tone.
Melodic minor scales
The harmonic minor scale has another problem. The distance between its sixth and seventh scale degree is unusually big: the augmented second. This sounds quite unusual in a melody. To solve this problem, in an ascending melody which leads to the tonic, the sixth scale degree of the natural minor scale is also raised. In a descending melody which moves away from the tonic, we do not have to lead to the tonic. In this case, we do not raise the sixth or seventh scale degree of the natural minor. Because it solves the problems present in melodies in the harmonic minor scales, such a minor scale is called a melodic minor scale.
The melodic minor scale is different when it is played ascending than when it is played descending. This is shown in the next figure.
Figure: The ascending and descending A melodic minor scale
The structure of ascending melodic minor scales is defined by the list of the major and minor seconds: M2, m2, M2, M2, M2, M2 and m2. The last minor second leads us to the tonic again, only now it is one octave higher. We see that ascending melodic minor scales have the leading tone. The descending melodic minor scale corresponds to the natural minor scale, only it is played descending.
In the figure, we see the symbols for the ascending and descending sixth and seventh scale degree. When we speak about scale degrees, we must specify relative to which scale they are given. Especially, if we talk about the sixth or seventh scale degree of a minor scale, we must specify the natural, harmonic or melodic minor scale. For instance, the seventh scale degree of the A natural minor scale is G while the seventh scale degree of the A harmonic minor scale is G#. The ascending seventh scale degree of the A melodic minor scale is G# while the descending seventh scale degree of the A melodic minor is G.
Examples of harmonic and melodic minor scales
In chapter Scales and key signatures, we found key signatures that enable us to write the natural minor scales in the most readable way i.e. without using accidentals. We use the same key signatures with the harmonic and melodic minor scales. For instance, we already wrote the A harmonic minor scale and the A melodic minor scale, both in the C major/A minor key signature – the same key signature we use for writing the A natural minor scale.
The next figure shows the harmonic minor scales in the key signatures with up to four sharps and flats.
Figure: The harmonic minor scales in the key signatures with up to four sharps and flats
The next figure shows the melodic minor scales in the key signatures with up to four sharps and flats.
Figure: The melodic minor scales in the key signatures with up to four sharps and flats