There are three types of minor scales:
- The Natural Minor scale
- The Harmonic Minor scale
- The Melodic Minor scale
The natural minor scale includes the same notes as its relative major. For example, A natural minor contains the same notes as C major but A is its tonic instead of C.
The harmonic minor scale also contains the same notes as its relative major but its seventh degree is raised
in this case G is raised to G sharp. This was initially done so that the harmonised fifth degree (the Dominant) would produce a major triad as opposed to a minor triad, as is found in the harmonised natural minor scale.
The melodic minor scale has two forms, the ascending form and the descending form.
Its descending form is the same as the natural minor scale
while the ascending form raises the sixth and seventh degrees
in this case the F and G are raised to F sharp and G sharp respectively. The augmented 2nd interval between the sixth and raised seventh degrees of the harmonic minor scale led also to the raising of the sixth degree in the ascending form of the melodic minor scale. That is not to say that there are instances where composers do use the raised sixth and seventh degrees while descending and the lowered sixth and seventh degrees while ascending.