5.9 Minor scales: the melodic and harmonic forms
The second form of the A minor scale, the melodic form, has two types of intervallic structure – the ascending structure is different from the descending structure. The descending pattern is the same as the natural form covered in the previous section. The ascending pattern is as shown below:
The intervallic structure of the melodic form of the A minor scale (ascending). The descending structure is the same as for the natural form of the minor scale
Symbolically, this ascending structure can be represented as T S T T T T S.
Example 51 shows the A minor melodic scale, both ascending and descending.
In the ascending version, notice that the need to raise both the F and the G to F♯ and G♯ respectively does not affect the key signature – these sharpened notes are simply ignored. Instead, when F♯s or G♯s are required in the music, the sharps have to be written in for each note, or at least as often as is necessary. We’ll consider the guidelines for how to deal with this in Section 6 on accidentals and we’ll also discuss the role of another accidental, the natural, shown by the symbol ♮. In Example 51, the bracketed naturals remind us that, whereas in the ascending scale the F and G become F♯ and G♯ respectively, in the descending form the G and F remain as G and F.
The third and final form of the A minor scale is the harmonic minor (which has the same intervallic structure both ascending and descending). It contains elements from both the ascending form of the melodic minor (the G♯) and the descending form (the F). The consequence of this is that the interval between F and G♯ is a tone plus a semitone, an interval that we haven’t met in a scale before:
The intervallic structure of the harmonic form of the A minor scale. The structure is the same both ascending and descending
|F–G♯||Tone + semitone|
Symbolically, this ascending structure can be represented as T S T T S T + S S.
The A minor harmonic scale is shown in Example 52. Again, the need to raise the G to G♯ does not affect the key signature, which, as you know, has no sharps or flats.
It is true that minor scales are more complicated than major ones. However, the differences between the three forms are less complex than a quick glance might suggest. If we compare the three forms of the A minor scale (see Example 53), you can see that these differences relate to only two questions: (i) whether the sixth note and/or seventh note up the scale is sharpened, and (ii) whether the ascending and descending forms of the scale are the same. So the differences are not as great as it might first appear. The first five notes of each of the three forms (when ascending, and the last five notes when descending) are exactly the same, and, as noted earlier, the descending form of the melodic minor has the same intervallic structure as the natural minor.