leeniea, my students call the Harmonic Minor the "Arabian Nights" scale - pretty close to belly-dancing! :>)

It's the augmented 2nd between the 6th and 7th notes, created when the 7th is raised, that gives the scale it's 'exotic' sound, even though it's rarely found in "Middle Eastern" music per se. Composers in the pre-Baroque era began to raise the 7th note of the natural minor scale (the Aeolian mode) because it gives more "pull" to the leading note, as it "leads" back to the tonic, which establishes the tonality much more strongly.

If you look a major scale, you'll notice that it ends with a semitone between the leading note and tonic. If you play it, and stop on the 7th note rather than the tonic, you'll notice how "unresolved" it sounds and feels. That leading note just "NEEDS" to go "home" to the tonic, and the ear remains "unsatisfied" until it does. As the "tension" is resolved on the tonic note, the home key is firmly established for the listener.

Compare this with the natural minor scale now - notice how the unaltered form ends with a whole tone between the leading note and tonic. Play it, stopping on the 7th, and you'll notice that the "pull" to the tonic is much weaker. By raising the leading note, producing a semitone between LN and tonic as in the major scale, the satisfying "pull" of the LN resolving on the tonic firmly established the tonality of the scale is achieved.

Why is it called the Harmonic Form? Because it makes such a important difference to the chords created within the minor key. Raising the 7th note changes the quality of the all-important dominant chord from minor to major, a significant harmonic difference! Again, the increased "pull" of the leading note to tonic as the altered V chord resolves on I (ie. the vital V-I progression, or perfect cadence), establishes the key much more firmly. Without the raised 7th, the V-I progression moves from a minor chord to another minor chord, much less effective than major to minor for establishing tonality. There's more information about it at this link.

The natural form of the minor is called "natural" because no notes are altered - it's the original Aeolian mode, the major scale starting on the 6th note.

Why the "melodic" form of the minor scale? Because raising the LN to lend emphasis to the tonic, as in the harmonic form, creates that awkward interval of an augmented 2nd between the 6th and 7th notes. "The interval between the sixth and seventh degrees of the scale is now a tone and a half which is uncomfortably wide when writing melody. It would be better if we could widen the interval between the fifth and sixth degrees, from a semitone to a tone, and narrow the interval between the sixth and seventh degrees, to a tone." By raising the 6th note as well, melodies are "smoother" and easier to play/sing. More information at this link.

As far as I know, both altered forms of the minor scale were well established centuries before the Romantic era. The works of JS Bach abound with examples of the melodic minor scale!

And as a piano teacher, I must add that it's just as easy to hear "wrong notes" in Romantic piano pieces like Chopin Waltzes as it is in classical pieces like Beethoven Sonatas. Where I find it more difficult is in 20th century atonal/polytonal works. Unless you know them very well, they all sound like "wrong notes" to me!!

daylia