Ahh, the freebird progression.
My best understanding is that this is an example of referencing parallel key signatures. The G major and C major chords imply G major, but the flattened 3rd (the Bb major chord) is borrowed from the natural/melodic minor key of G. I've seen this progression with D major tagged on the end too; the dominant chord from the G major scale. So.. yeah, G major with a borrowed chord from that parallel minor seems to be an answer.
I guess you could also be writing in C major, but the Bb major chord is again borrowed from the minor of C. (as chunter mentioned above)
There are a number of options for what scale to write the melody in. Alternating between the mixolydian on G (G-A-B-C-D-E-F-G) and the dorian on G (G-A-Bb-C-D-E-F-G) can work. Basically, all you're doing is changing the identity of the 3rd.
There's probably a better explanation that I've missed, to be honest.
n00bstar wrote:Also.... and this is where I started to mentally masturbate too much with this... I was assuming I was in G Major with a borrowed chord. So for my middle eight I went to the relative minor, Em, and now I can't make it resolve back to a G, it wants to resolve on the Em every damn time no matter what twisted fucked up path I take through the chords.
ARGH.
Try and set yourself up for some kind of cadence (eg. end a progression on D major or C major/minor or something so that you can head on back to G.... Be as interesting as you want)
Last edited by Fearofdark (Mar 28, 2013 10:24 pm)