Okay, folks. . . .

Right out of the music theory textbook that I have here in my lap.

D-E-F-G-A-Bb-C- D    —    This is D natural minor. Uses the same notes as its relative major, F. It's the same both upward and downward.

D-E-F-G-A-Bb-C#-D   —    This is D harmonicminor. And it is the same both upward and downward.

D-E-F-G-A-B(nat)-C#-D    —    This is the D melodic minor. Going up, the only difference between it and a D major scale is that the F is natural (in D major, the F is sharp). NOW: on the way back down, it's D-C(nat)-Bb-A-G-F-E-D.

The natural minor shares the same scale as its relative major.

The harmonic minor came into use because the melodic minor has no "leading tone." The "leading tone" is the seventh note of a scale, a half-step below the tonic (key) note, and harmonically, it creates a strong upward pull, calling for resolution to the tonic note or chord. BUT—it creates an augmented second interval between the sixth and seventh notes of the scale. If used consistently within a piece of music, it gives the piece a characteristic Middle-Eastern sound, which may not be desirable. So—

This called for the development of the melodic minor scale. Going upward, it sounds minor because of the third degree of the scale, then moves smoothly upward without the jump between the sixth and seventh degrees, and the seventh degree is a proper leading tone. On the way back down, it returns to the same scale as the natural minor (otherwise, it would sound like a major scale until you hit the third, which might sound a bit odd.

It's in the book.

Got all that?

Don Firth