Harmonic minor scales are same as natural minor scales except that the seventh degrees of them are raised by one half step.
Harmonic Minor Scales
When we rise the seventh degree, we create an augmented second interval between the sixth and the seventh degrees of the scale. So that, it becomes a leading tone to the tonic in a similar way to major scales. Harmonic minor scales follow this pattern of whole steps and half steps between their notes:
Whole-Half-Whole-Whole-Half-Whole and a half-Half
On higher or lower octaves this pattern repeats. Note that this pattern only occurs on ascending harmonic minor scales. When descending, it is reverse of this. There are several ways to build a harmonic minor scale. The easiest way is just raising the seventh degree of the relevant natural minor scale by a half step. Let’s have a look at an example.
A Harmonic Minor Scale
This is A natural minor scale. To build A harmonic minor scale, we just have to raise the seventh degree of A natural minor scale by one half step. The seventh degree of A natural minor scale is G. By placing a sharp to this note, we can raise it by one half step and build A harmonic minor scale.
Building Harmonic Minor Scales with Tetrachords
All harmonic minor scales have minor tetrachords (Whole-Half-Whole step pattern) as lower tetrachords and a harmonic tetrachords (Half-Whole and a half-Half step pattern) as upper tetrachords with whole steps between them. If we start with any note and maintain this pattern, we can build a harmonic minor scale in no time. Let’s see an example. Let’s say we want to build F harmonic minor scale now.
F Harmonic Minor Scale
F Minor Tetrachord
First thing we should do is building the lower tetrachord which is F minor tetrachord. We should place the notes: F, G, A and B.
The step pattern between these notes is W-W-W. But we want this to be a minor tetrachord pattern which is W-H-W. The interval between G and A is problematic. We should narrow this interval down to a half step. If we alter G the previous interval will be altered too. This is why we should alter the note A. We place a flat to this note. When we do this, the interval between G and A flat will be a half step. But then the interval between A flat and B will be problematic too. So we will place a flat to B too to make that interval whole again.
C Harmonic Tetrachord
Obviously, it starts with the note C which is a whole step ahead of B flat, the last note of the F minor tetrachord. Then we add three more notes alphabetically: D, E and F.
As you can see, this is already a major tetrachord with Whole-Whole-Half step pattern. We want this to be a harmonic tetrachord which has Half-Whole and a Half-Half step pattern. We don’t alter the first note C. Because if we do that, we alter the previous intervals of the scale too. This is why the only way to change the interval between C and D is placing a flat to D. When we do that, we also alter the next interval. In fact, we enlarge it from whole step to whole and a half step which we already want that to maintain the harmonic tetrachord step pattern. The interval between E and F is okay, so we don’t alter it.
We combine these two tetrachords to build F harmonic minor scale.
This is how we build F harmonic minor scale with tetrachords. Of course, we can just build F natural minor scale, then raise its seventh degree by a half step too.
Building F Harmonic Minor Scale By Altering Its Natural Minor Scale
In this figure, you can see that the seventh degree of F natural minor scale is E flat. To raise this note by a half step, we can just place a natural.
Notice that we actually place the natural sign on the seventh degree when we want to represent this scale with a key signature. Because unless we place anything else to the notes, the accidentals in the key signatures are valid for those notes. So if we don’t place the natural sign on E, we should consider it as E flat, thus this scale becomes a natural minor scale. But when we alter it with natural, it is now E natural which sounds same as E and this scale is a harmonic minor scale.
All Harmonic Minor Scales
Let’s have a look at all harmonic minor scales.