The differences between natural, harmonic and melodic minors?

Question

I'm studying scales and came across the natural, harmonic, and melodic minors. I understand the patterns for each scale but what other important differences exist between the three?

Answer 1

There are four minor scales.

All four of them contain the same pentachord formula on the bottom:

R 2 b3 4 5

The difference is in the permutations of the 6th and 7th degrees.

The 6ths and 7ths can either be natural or flat.

In common practice, the composer or arranger can choose relatively freely the qualities of those respective scale degrees.

Berklee terms this family of four minor scales "The Composite Minor".

One common example is a minor piece that remains in the natural Aeolian throughout, except when it comes time to effect a strong cadence at which point the 7th degree is raised to become the leading a half-step below the tonic root.

Another instance is the fluidity of Aeolian vs Dorian in "Stairway to Heaven". It's in one version of A composite minor:

When the underlying current chord is an F major it is Aeolian, yet when they underlying chord is D major it is in Dorian.

Characteristics of the composite minor famly:

Aeolian = b6 / b7

Dorian = nat6 / b7

Jazz minor = nat6 / nat7

Harmonic minor = b6 / nat 7

Answer 2

It's all based on the mood that you want to go for. Natural (also known as the Aeolian mode) sounds a lot more plain, whereas harmonic minor can sound a lot more exotic/give you an extra kick because of that #7 in the scale. Each scale has a particular color for itself, and due to the nature of each one's color you might find certain minor scales fitting in better for certain situations if there's a specific emotion you're trying to evoke. Hope this helps, and feel free to ask any follow ups!

Answer 3

The so-called "natural" minor scale can be thought of as the base minor scale. If we were to play from A to A on the piano using only the white keys we would be playing an A natural minor scale. Sometimes this is called the Aeolian mode.

Now, you may notice how the natural minor scale lacks a leading tone. Instead, between the 7th scale degree and tonic there exists a whole step. Now, that's fine, but it could be better. We can really increase that tension and magnetic pull from the leading tone (scale degree 7) up to the tonic by raising that pitch up by a half step. Think of the sound from "ti" to "do," or play G# to A on the piano; this has a stronger pull up to tonic, A, than "te" "do" or G to A. Looking a bit deeper we can see that raising that leading tone enables us to have a major harmony built on the 5th scale degree, which is the all-important Dominant. With the natural minor scale we would have EGB, which is an E minor chord. Raising that leading tone gives us EG#B, a nice solid major dominant. This is why when we simply raise the leading tone of the natural minor scale we call it the Harmonic minor scale, because we altered a pitch in favor of creating that dominant harmony.

If we were to play that harmonic minor scale, though, we might notice how from scale degree 6 to scale degree 7 (F to G#) we have what SOUNDS like a minor 3rd, but since it is a scale and they are neighboring pitches, is actually an augmented 2nd. That's kind of weird to have, so let's just go ahead and smooth out that kink by raising the 6th degree up to F#, which gets rid of any augmented intervals. Now F# to G# is a major 2nd. Problem solved. That's your melodic minor scale.