Why is there no fourth minor scale with a natural 6 and a flat 7?

Question

These scales are considered the minor scales:

natural:  1  2 b3  4  5 b6 b7
harmonic: 1  2 b3  4  5 b6  7
melodic:  1  2 b3  4  5  6  7  (ascending)

However, this scale:

4th min:  1  2 b3  4  5  6 b7

is referred to as the Dorian mode, but not as a minor scale. Is there a reason, besides maybe that it isn't used as often as the other three, for not giving it a name like, say, the sardonic minor scale? Is there something inherent in this scale that doesn't lend itself to minor harmony?

Wikipedia states that:

[The Dorian mode] may be considered an "excerpt" of a major scale played from the pitch a whole tone above the major scale's tonic , i.e., a major scale played from its second scale degree up to its second degree again. The resulting scale is, however, minor in quality (...)

So if it is a scale that is "minor in quality", why is it not the fourth minor scale?

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To be clear: I'm not so much concerned with this scale not having a name, but rather with the absence of a name implying that it isn't a useful scale. If you have a minor scale with a flat 6 and 7, a minor scale with a natural 6 and 7, and a minor scale with a flat 6 and natural 7, why not have one with a natural 6 and a flat 7? Why is this scale so useless that you wouldn't even bother to label it?

Answer 1

The minor scales (natural, harmonic, and melodic) are intended as descriptive of compositional practice.

The dorian and aeolian (minor) modes are permutations of the major scale and have different functional meaning.

The dorian mode is actually quite a lot older than the minor scales: its modern form dating back to the early church modes, and that named after the even earlier Greek mode that used similar intervals.

However, it jazz and popular music, dorian is considered a minor mode, as it works well against minor chords and, especially, minor seventh chords.

For some relevant discussion, see Difference between keys and scales?

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Update

A brief explanation of why Dorian isn't considered a "functional" minor scale:

• Natural minor: occurs "naturally" as a mode of major; however it lacks a leading tone.
• Harmonic minor: has a leading tone; however, it also has a "weird" augmented second.
• Melodic minor: has a leading tone when ascending, when it's needed, but also a raised sixth to avoid the augmented second. Going down, though the leading tone is not needed, so neither is the raised sixth.
• Dorian has a raised sixth, but no leading tone, so serves no special purposes in major/minor tonality.

Answer 2

OK, it's the 4th minor scale. And Mixolydian is the 2nd major one.

It's interesting to know whether a mode is major or minor in quality. Maybe, if you're really into labelling, interesting to debate whether Locrian is minor or in a diminished class of its own. We don't normally number them within these categories. But you can, if you like.

Historically, at least in the Common Practice era, functional harmony - dominants going to tonics - was the predominant framework. The useful modes were those that contained a perfect 4th and major 7th, ones you could build a dominant 7th chord in. Major, Harmonic Minor and (at a pinch) Melodic Minor. So, when the language of music theory was established, these were considered more important.

When I started noticing music theory, in the 1950s, Natural Minor wasn't mentioned much. We KNEW about it, as we knew about the other 'antique modes'. But it wasn't really a part of the functional harmony taught in schools. (Yes, I know, this was 80 years after Debussy, 50 after Stravinsky. Pedagogy often takes time to catch up!)