The distinctive sound of the harmonic minor scale comes from the augmented second between its sixth and seventh scale degrees. While some composers have used this interval to advantage in melodic composition, others felt it to be an awkward leap, particularly in vocal music, and preferred a whole step between these scale degrees for smooth melody writing. To eliminate the augmented second, these composers either raised the sixth degree by a semitone or lowered the seventh by a semitone.
The melodic minor scale is formed by using both of these solutions. In particular, the raised sixth appears in the ascending form of the scale, while the lowered seventh appears in the descending form of the scale.
