In the traditional sense, melodic minor has an ascending form and a descending form, meaning that the notes in the scale changed based on whether you are playing up the scale or down the scale. When the 7th degree of any scale is a half-step away from the root it is called a leading tone, and so the important difference between the natural and harmonic minor scale is that one has a leading tone while the other does not. In other words, in a natural minor scale the 7th scale degree is a minor 7th, whereas in a harmonic minor scale the 7th scale degree is a major 7th (and will be a half-step away from the root of the scale). The harmonic minor scale differs from the natural minor scale in only one way – the 7th scale degree is raised by half-step. (And remember that when in a major key, the relative minor scale can be constructed simply by using the same pitches but treating the 6th scale degree as the starting note). For this reason we can say that F natural minor is the relative minor of Ab major. This is the same key signature as the key of Ab major.

Looking at our newly created F natural minor scale, we can see that we have 4 flats in the scale, and so the key signature would read Bb, Eb, Ab, and Db. The natural minor scale is related to a major scale because it shares the same key signature as a major scale. In our example above using the F major scale, this means we will be lowering the A (the 3rd) to Ab, the D (the 6th) to Db, and the E (the 7th) to Eb. In order to create a natural minor scale, we simply start with the major scale and lower the 3rd, 6th, and 7th scale degrees by a half-step. In other words, they are all versions of a minor scale, with slight but significant differences among each. Natural, harmonic, and melodic minor are simply various forms of the minor scale. As you can see in the scale above, each note of the major scale is given a number (a scale degree) which represents its placement or order within the scale.

B-flat melodic minor scale