Notice I qualified it with "or at least a key/mode of three flats" and that's ultimately what I mean. That the path of least resistance is for the piece to sit within a key signature of three flats, which would allow all of the chords except the C major to be diatonic. If the progression sounds like C minor (C Aeolian to be exact, because of the minor v chord) and then we instead get C major, there's an historical precedent for this kind of usage, the Picardy Third.Martin Gifford wrote:Don't see how the path of least resistance is to say C minor when the first chord is C major.
Jazz guy here, and I wouldn't say C Mixolydian mostly because there's no evidence of an A-natural being in the piece judging from the chords we've been given (as I pointed out previously). There is an A-natural in the C Mixolydian scale. This is why it's weird to apply C Mixolydian and then say that Ab is the odd man, when we've never seen another type of "A" to tell us what a "normal" A would be in the context of this progression. See what I mean?Martin Gifford wrote:I reckon any jazz guy would say C mixolydian.
Maybe the confusion here is that modes are generally applied to modern music in two ways: (1) jazz chord/scale theory where each chord has a corresponding mode that one can play over it, and (2) true modal music where the melodic phrasing outlines an actual "Mixolydian" or "Dorian" sound.
Your application of C Mixolydian seems to sit somewhere in between those two. Just from playing the chord progression through I certainly don't get an overall sense of C Mixolydian from it, which strikes modal usage number 2. And as I've already said there's no A-natural to be found, which strikes modal usage number 1.