This is a topic that I think is covered poorly sometimes. It's one of those things that is actually a much longer discussion. Think of it, in increasing complexity,
1. There is a major scale and a minor scale.
2. Actually, there are three minor scales: natural, melodic, and harmonic.
3. Actually, forget about those scales. Think instead more freely about tonality, modal mixtures, secondary dominants, and voice leading.
I think that anyone studying music is better off stopping at #1 or going all the way to #3. The problem with stopping at viewpoint #2 is that it's complex enough to make you really think, but not grounded enough in actual musical practice to make that thinking fruitful[1].
There are a lot of reasons why you might want a particular note to be sharp or flat. Sometimes you want a stronger resolution, like V -> i, rather than v -> i, which sounds weak. For that reason, to make better harmony, you may choose to make the 7th scale degree (B) a major 7th (B natural) instead of a minor 7th (B flat). You may also want to resolve a melodic line by half-step, which often sounds stronger, like B->C. But when you are stepping downwards, C->B, that's likely not any kind of resolution, so C->Bb is fine (it's likely not a resolution if you're in the key of C). These melodic concerns drive the "melodic" minor scale (and we drag in the 6th scale degree to avoid an augmented second interval).
The catch is... all we're really saying here is,
1. You are free to borrow notes from outside the key, for lots of reasons, and
2. There are lots of reasons in particular why you might want to borrow for the sixth and seventh scale degrees.
These deeper concepts get shoehorned into the notions of "melodic minor" and "harmonic minor". So much is lost by shoehorning these ideas into scales that I wonder why we even bother. I think it's really that people like categorizing scales and learning new names for things, which also drives people's fascination with modes, which is totally out of proportion to how much you'd actually want to use them in music. Modes and scales seem to have a particular fascination for hackers in the music scene.
I have a lot more to say on this subject, but I'm working on a blog post.
[1]: Please note that you definitely can choose to write music using one of these scales as a device, and many people do, and it's good stuff. It's just that most music that most people listen to doesn't make any sense to analyze as using particular minor scales.
Yes, the "harmonic" and "melodic" so-called scales are more like common musical patterns that arise by "borrowing" chromatic alterations from the parallel major scale for the sake of better resolution. This also explains why the "melodic minor" is different when going upwards vs. downwards; since it's not really a "scale" in any structural sense, and the idiomatic alterations are different when one is "resolving" in one direction or the other.
>I think it's really that people like categorizing scales and learning new names for things, which also drives people's fascination with modes, which is totally out of proportion to how much you'd actually want to use them in music
I don't get this. Modes show up all the time in popular music of the last 50 years. Am I missing something?
Would love to see an attempt to quantify how they show up "all the time".
When these discussions pop up, you see a lot of examples of songs that have borrowed chords or modal mixtures... "Oh, this song uses a mode in the bridge, or that song uses a mode except for the intro, or this other song switches between two modes." When songs have a lot of borrowed chords or borrowed notes, it more or less subsumes the idea of modes.
The problem is that modes are somewhat fragile things. As you mix more borrowed notes and borrowed chords into a song, the notes that make a mode sound like a mode get drowned out, and you're left with just a key center and a tonality (or not even that). That leaves precious few popular songs that actually sound like they're using a mode.
There are some specific genres where you see certain scales over and over, like the mixolydian scale in blues music, but blues typically relies so heavily on mixed tonalities.
1. There is a major scale and a minor scale.
2. Actually, there are three minor scales: natural, melodic, and harmonic.
3. Actually, forget about those scales. Think instead more freely about tonality, modal mixtures, secondary dominants, and voice leading.
I think that anyone studying music is better off stopping at #1 or going all the way to #3. The problem with stopping at viewpoint #2 is that it's complex enough to make you really think, but not grounded enough in actual musical practice to make that thinking fruitful[1].
There are a lot of reasons why you might want a particular note to be sharp or flat. Sometimes you want a stronger resolution, like V -> i, rather than v -> i, which sounds weak. For that reason, to make better harmony, you may choose to make the 7th scale degree (B) a major 7th (B natural) instead of a minor 7th (B flat). You may also want to resolve a melodic line by half-step, which often sounds stronger, like B->C. But when you are stepping downwards, C->B, that's likely not any kind of resolution, so C->Bb is fine (it's likely not a resolution if you're in the key of C). These melodic concerns drive the "melodic" minor scale (and we drag in the 6th scale degree to avoid an augmented second interval).
The catch is... all we're really saying here is,
1. You are free to borrow notes from outside the key, for lots of reasons, and
2. There are lots of reasons in particular why you might want to borrow for the sixth and seventh scale degrees.
These deeper concepts get shoehorned into the notions of "melodic minor" and "harmonic minor". So much is lost by shoehorning these ideas into scales that I wonder why we even bother. I think it's really that people like categorizing scales and learning new names for things, which also drives people's fascination with modes, which is totally out of proportion to how much you'd actually want to use them in music. Modes and scales seem to have a particular fascination for hackers in the music scene.
I have a lot more to say on this subject, but I'm working on a blog post.
[1]: Please note that you definitely can choose to write music using one of these scales as a device, and many people do, and it's good stuff. It's just that most music that most people listen to doesn't make any sense to analyze as using particular minor scales.