I am interested in the underlying scale and chord structures of ragtime music . For example, I was reading in my book Jazzology last night that ii-V-I progressions are frequently used in Jazz. I am interested in the corresponding ones for ragtime music.
Are there scales and chord progressions particularly used in Rag music?
Structurally ragtime harmony is pretty much classical tonal harmony, but there are some idiomatic specificities that give ragtime its characteristic sound.
One progression very characteristic of ragtime is the so called... ragtime progression (although it was used before, even in classical music, it was mostly popularized in ragtime). It's made of a succession of "piggybacked" secondary dominants in a succession of rising 4th intervals onto the tonic, e.g., in C, in its full extension:
C - E - A - D - G - C (in this instance I find chord note names easier to use than the roman numeral analysis that would be required)
Usually, all chords are dominant 7th chords. The progression may start in any of the secondary dominants, the most common case being a 4 step progression (starting on A for a piece in C).
Another variation superimposes a ii-V-I progression by making one of chords minor (also usually 7th)
C - A7 - D-7 - G7 - C
There is also a lot of chromatic substitutions, usually dictated by voice leading (i.e. chords changing by step intervals, mostly half tones) thus creating a lot of full and half diminished (7th) chords.
Just to give an example, at the end of the B part Scott Joplin's Maple Leaf Rag (Ab major), the progression is:
Notice how the first chord of the "ragtime progression", F in this case, is approached chromatically in a quite seamless way. Then the progression follows pretty much plainly (no no-chord-tones for two bars). In bar 4, at the point marked with *, Bb- is replaced by Bb7add9 both providing harmonic interest and smoothing voice leading: notice how the uppermost and lower "treble" voices move stepwise.
Regarding scales, my understanding is that structurally they are mostly diatonic, I don't think that pentatonic or blues scales are inherently used, although sometimes a "bluesy" sound may occur by means of the harmony. Melody is not a strong component of ragtime anyway, many ragtimes almost have no melody as such, or melody is built practically with arpeggiated chords and a lot of chromatic passing tones (Mapleleaf Rag a case in point).
I'm going to tell you what I observe in very layman's terms without music theory terms.
Let's for simplicity we're in the key of C.
A lot of them have this progression: (F F#° or Ab7 /) C/G A7 D7 G7 C especially towards the end of a section.
A possible "verse" (very common) is
C / / / | / / / / | F / / / | C / / /
C / G/B / | Am / Am7/G / | D7 / / / | G / / /
C / / / | / / / / | F / / / | (C or E7) / / /
F / F#° / | C/G / A7 / | D7 / G7 / | C / / /
There are lots of C6s and F6s scattered throughout, especially when you get to the "second section", and that second section (quite often) starts with G.
There may be a few diminished chords, usually C->C#°->D, D->D#°->C/E, F->F#°-C/G, A#°->G/B, for example.
In quite a few of them, there is the trio section, which is going to be in a key a perfect 4th from your starting key. In this case, that trio section will be in F.
My apologies for my dilettante approach to this.
