#1
ok so for descending on a melodic minor scale are you supposed to play natural minor? if you are... is it a common technique to just descend on the melodic minor anyways?
#2
you use the natural minor because the melodic minor only exists to preserve the leading tone, when descending you do not need it so you use the natural minor
#3
Old theory says that you play Natural Minor on the way down, but it's uncommon in modern music. It was done because the b6 leads nicely to the 5. The 7th was lowered because harmonic minor (which it would be if you only lowered the 6th) sounds dissonant.
#4
you use the natural minor because the melodic minor only exists to preserve the leading tone, when descending you do not need it so you use the natural minor


The leading tone exists in harmonic minor, which was created to provide a major V chord. Unfortunately, the resulting augmented 2nd interval sounded dissonant in a melody line, which is why the sixth was raised as well. It is almost never played differently ascending a descending in modern music. You really don't have to worry about it.
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#5
One more thing: If you're playing Melodic minor over a m6 chord, you SHOULDN'T play a b6, and if you play melodic minor over a m/maj13 chord, you SHOULDN'T play the b6 or b7.

Of course, do what you want if it sounds good, but those notes will clash and that isn't always desired.
#6
Quote by Galvanise69
So the minor on the descending is only played in old music, i think, but i still dont understand why
If you mean that the melodic minor is played as Natural Minor when descending in old music then you're correct. It is done because the b6 pulls your ear towards the 5 and the 7 is lowered so there is not an awkward interval between the 7 and the b6.
#7
Quote by Galvanise69
So the minor on the descending is only played in old music, i think, but i still dont understand why


All I can think of to answer you is that it most likely has to do with the progression of popular classical pieces. The most common classical minor progression would be i, ii, III, iv, V, VI, vii(fully diminished). As you can see, the dominant V and the major III(and not a III+) would need to be derived from a different scale(natural instead of harmonic). Also the preference for the VI instead of a vi(fully diminished) would again need two different scales(natural OR harmonic instead of melodic. I don't really think I explained it well...but certain changes had to be made to avoid the major IV(in melodic), the fully diminished vi(in melodic), the augmented III(melodic and harmonic), and the fully diminished ii(natural and harmonic). But it's theory...emphasis on the word "theory".

I also believe that composers altered things to best suit different instruments and/or choral writing.
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