There is a bluegrass song archetype that mixes the minor/major 3rd and raised/lowered 7th making almost an extended scale. How can I describe what's going on here using music theory?
Modal mixture comes to mind but it doesn't seem like a fleeting thing, affecting only a single chord, rather it's pervasive through the entire harmonic texture.
Is this trying to apply a framework that just doesn't fit for this type of music?
Pretty polly -
I could produce more examples if needed
It's basically blues. Major key music inflected with blue notes. The rhythm accompaniment patterns are what make it specifically bluegrass.
Most of the time the harmony - heard most clearly by following the bass - is one chord B major. But while the bass spends most of the time thumping along with roots and fifths of a B major chord it will do a little walking bit at the end of phrases that gives an F# chord (chord when you consider the whole ensemble.) Sometimes that walking part goes up through an A but I have trouble hearing if it's really an A# for a leading tone (to make a clear F# major chord.) It may be a little lower than A# but the overall sense to me is B major and F# major chords.
In the melody parts you will get the play between major/minor third and major/minor seventh. Those are simply blues tones. You can think of that as an extended scale if you like, but it isn't a unique or problematic thing. In "classical" minor key music the sixth and seventh scale degrees are variable too. The only "problem" this presents is mistaking a tonality with a fixed scale of seven tones. Blues is a tonality not a scale. Minor key is a tonality not a scale.
I think an important thing to mention is that while the melody parts will use the minor third and seventh for a blues sound they may freely clash with the major intervals in the accompaniment parts. When the B major chord is played - with a D# for a major third - in the accompaniment the melody part may use D natural. That clash - technically you can call it a chromatic cross relation - is part of the blues sound.
The fact that this song spends most, but not all, of the time on the tonic chord (B major) has no bearing on the tonality. Although it is a characteristic of some folk music.
Keywords here are blues scale, and even more importantly blue notes. See: https://en.wikipedia.org/wiki/Blue_note Blue notes appear in various styles, particularly often in blues, but also in jazz, rock and others. Various musicians, using various instruments play them differently, e.g. by playing note in between two pitches, sliding between them, playing microtonal bends, grace notes...
If someone tried to describe this song to me by saying it's "modal", I would think of something completely different. It's bluegrass, with bluesy bends in the melody. I'd guess that even the most pathologically classically oriented music theorists must have encountered the term "blues" by now.
Some anonymous Internet writers have written a Music Theory article on Blues: https://en.wikibooks.org/wiki/Music_Theory/Blues
No mention of modes or modality has been deemed necessary to describe "blues"!
Quote:
Another common practice in blues is to play the entire song over a single chord...
What comes to chords, there are chord changes in the Pretty Polly example song, one V chord in the end of every verse, and between 4:04 - 4:09 they even hold the V chord F# as a final high-point of the song.
This tune is 100% modal, and it uses a single scale from beginning to end.
Now, please note that "modal" doesn't mean "using one of the seven major scale modes". "Modal" describes any music which is built around a scale -- any scale -- rather than on the combination of chords and melody.
For example, Indian classical music is modal, while Western pop, rock, and classical music are not, being based on harmonic progressions. (Exceptions exists but are vanishingly rare, e.g. Pink's song "Get this party started", is a rare example of a modal pop song. You'll notice that there are basically no chords, it's just a B minor scale)
Blues and bluegrass may fall in either camp -- if you play a blues in which the chord progression is in evidence, then the harmony dominates, and the melody and improvisation is forced to follow the chords. But if the chords are not used, or limited to a single chord, then the improvisation becomes an exploration of the scale, just like in the video above. And then what you have is essentially a modal tune.
Similarly, most Jazz is not modal, as chords are central to most Jazz tunes, but if you leave chords aside, or use just a single chord for an extended period, the music takes a modal flavor immediately.
Bottom line, whether the scale has minor thirds, or major thirds, or both, is not the point -- if there is no chord progression, and the star of the piece is the scale itself, that's what modal music means in general.
The two key notes you've picked up on - M3/m3 and M7/m7 - are the hub of the blues scale notes - along with P5/d5, also featured.
Strangely, in a major key (this song is in B major - one chord, all through!) although the 3rd, 5th and 7th notes all fit perfectly well, by playing or singing them a semitone lower works too. In a sort of 'sweet and sour' way, as a student once told me.
So, no, it's neither modal nor multi-modal. It's blues. Might even consider calling it bluesgrass..?
