Why do the notes of Melodic-Minor Scale change when you play it in descending order?

Question

Okay I'll admit, I don't know everything about music theory but I was pretty sure that any given diatonic (7 note) scale contained particular notes that defined the scale and were unique to the scale and that those notes would be the same regardless of which direction you were moving in said scale (ascending or descending).

Then I came across This Question which is specifically about the A-Minor scale and more particularly apparently about the A-Melodic-Minor Scale.

The accepted answer claimed

You play G-natural and F-natural when descending in a Melodic-Minor Scale

and a different user posted in a comment

A melodic minor has two extra sharps on the way up and none on the way down.

I had a hard time believing that the A Melodic-Minor scale (or any other Melodic Minor Scale) would have different notes depending on if it was played in ascending or descending order so I turned to my favorite search engine and found this on basicmusictheory.com about the A Melodic-Minor Scale:

Be aware that when descending this scale, sometimes the notes of the A natural minor scale are played instead.

So basically I learn that when you play the A Melodic-Minor scale on piano you play these notes when ascending:

But when descending it is often played with the notes pictured below:

This apparent aberration in logic is not specific to the A Melodic Minor scale but rather applies to any and all Melodic Minor Scales. So this question is not about just the A Melodic Minor Scale but rather ALL Melodic Minor Scales.

I am sure there actually is some logic to this unexpected revelation - but I would like for someone to explain why in a melodic minor scale the notes can vary depending on which direction you are moving in the scale.

Also - is the melodic minor scale the only type of scale where this commonly occurs?

Answer 1

The way that the Melodic Minor scale is presented to students (Melodic Minor when ascending, Natural Minor when descending, see ex. 1) is merely a teaching tradition. This tradition is an incomplete definition of how the great composers employed the Melodic Minor Scale in their melodies.

The apparent purpose is to allow the student to demonstrate mastery of both the scales, in a way that sounds pleasant to the listener.

In reality, the Melodic Minor scale (raised 6th and 7th scale degrees) may be implemented when ascending and descending (see ex. 2); there are many examples of this in the writing of Bach, Vivaldi, Quantz, Beethoven... almost any prolific "common practice era" composer (i.e. the Baroque through the Classical and Romantic periods).

Likewise, the Natural Minor scale may be utilized both when ascending and descending, but will not support the leading tone (e.g.: in A Minor, the 7th scale degree is G, but as a leading tone must become a G#). This note will occur inherently as the 3rd within the dominant chord (e.g.: in A minor, the dominant chord is E major or E7, both which include the G# note as the 3rd of the chord). But this note is not required to appear in the melody - it can be represented anywhere else in the voicing of that harmony/chord (see ex. 3).

Those who disagree with this analysis would argue that the most clear and final cadence in tonal music is the Authentic Cadence, where the harmonic progression moves from V to I (in A Minor: from E or E7 to Am). In order for the melody to reflect this harmony and resolve to the tonic, the 3rd note the V chord becomes the leading tone which should - by definition - resolve upward to the tonic (in A Minor: the G# note resolves to the A note). This note also occurs in other leading tone chords (in A Minor: the G# dim triad, the B dim7 chord, etc.).

The resulting scale is the Harmonic Minor scale, with its exotic sound created by the gap between the 6th scale degree and the #7 scale degree (in A Minor: the intervallic distance between F and G#, see ex. 4). Observe that when the Harmonic Minor scale descends the leading tone does not move upward - revealing another fallacy of teaching tradition.

The raised 6th scale degree is introduced into the line to smooth that gap (in A Minor: F# note to G# note to A note), resulting in the Melodic Minor scale (see ex. 4). This addition creates several interesting possibilities for harmonization of the melodic line, including an applied dominant chord (in A Minor: B7 supporting the F# note, to E7 supporting the G# note, to Am resolving to the A note) but there are numerous exceptions to this scenario as well.

In short, the Melodic Minor scale can be used ascending and descending:

• when the scalewise melodic line - descending from the tonic - does not drop below the 5th scale degree;
• when the underlying harmony is a prolongation of the V chord (or another harmony that has a dominant function);
• when the #6 and #7 scale degrees occur inherently in the melody (as when borrowing notes from the parallel major key); or
• when making use of repetition as a compositional device, stating and restating the #6 and #7 for emphasis.

Likewise, the Natural Minor scale can be used both ascending and descending:

• when the scalewise melodic line - rising from the 5th scale degree - does not rise above the 7th scale degree;
• when the passage does not include the V chord (or another harmony that has a dominant function); or
• when the leading tone (the #7 scale degree) does not occur in the melody.

Answer 2

The reason for the difference in ascending and descending comes down to how people composed in minor keys during the common practice period of music. To fully grasp the concept, you have to not only look at the melodic minor scale, but all three flavors of the minor scale which are the natural, the harmonic, and the melodic. Obviously the natural minor is derived from the natural occurrence of the scale in the major scale. The "melodic" in the melodic minor scale comes from how the melody is approached in a minor key just like the "harmonic" in harmonic minor comes from how the harmony is approached in a minor key. A full explanation can be seen in this answer this answer.

The ascending vs descending difference the idea of whether or not you are using the leading tone. When using the leading tone and stepwise motion to get to and from it, you would want to raise the 6th to avoid the augmented 2nd (which sounds like a minor 3rd) when going from the 6th to 7th scale degree to make the melody smoother. When you are not using the leading tone, you just use all the typical notes from the natural minor scale as you don't have that augmented 2nd interval.

The ascending scale naturally demonstrates the need for the 6th scale degree to be smoothed out when leading to the tonic while the descending it to show you the opposite case where you do not need to use the leading tone. While ascending to the tonic and descending from it is a good way to know which set of notes to utilize it is not the full picture and there is more to it then that. A full explanation of when you would want to use each can be seen in this answer .

Answer 3

The other answers cover all the important points. I'd just like to add that there's no "logic" behind the Melodic Minor scale, but merely musical taste, which is of course not set in stone.

For instance: sharpening the seventh step when it goes up, and flattening when it goes down, is not universal. O quam mirabilis est by Hildegard of Bingen has accidentals that do the opposite: the piece is in C ionian/mixolydian, and the seventh step, B, is natural at the top of the melody, going both up and down, and is Bb at the bottom, likewise going both up and down.

So while the melodic minor scale is indeed used in a lot of music, there are many exceptions: it's a style, not "logical".

Answer 4

After reading a lot of opinions I believe the only reason behind this when writing a melody:

• if a 7th is to resolve it leads to the tonic, that is going "upward"
• because 7th is naturalized 6th must also be naturalized to avoid a sharp-second interval
• when 7th is a passing tone or the composer want it to go "downward" instead of resolving it, it can just use the ordinary flat-7th + flat-6th, or nature-7th + nature-6th, long as it avoids the sharp-second interval
• of course if a sharp-second interval is specifically requested by a composer, and the singer, listener are both okay with it then this rule is meant to be broken, but it is called "melodic minor" because we know that to most people a sharp-second is not easy to sing or listen to

So, the melodic minor was only meant to express the logic (use leading tone to lead + avoid sharp-second), but it is presented as a scale, which usually has a designated and ordered set of notes, thus the awkward upward / downward difference.