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I'm familiar with the chord-scale system (https://en.wikipedia.org/wiki/Chord-scale_system) that dictate what scales go with what chord, and vice versa.

But I can't find much info about how jazz musicians choose WHAT chords and scales to play given this information.

For example, if a jazz pianist is putting together a tune or improvising something in C lydian over a C7 major chord, how'd they decide what chord or scale to move onto next? Stay in C lydian, but change the chord to G7? Keep playing over C7, but change the scale to harmonic major? Or do something crazy like change the chord to Caug, and play the whole tone scale?

So, are there any rules or guidelines that are used in jazz to decide:

1a) If one chord will sound 'good' (won't clam) after another chord

1b) Likewise, if one scale/mode won't clam after another scale/mode

2) When are good times in a song to change between chords and scales

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    Usually the chords are fixed and repeated during solos, then the scales that work with the chord progression are used by the soloist. Chord progressions are improvised in some cases, like jam bands, but that's a much harder thing to do in an ensemble and I don't know whether or not jazz bands do that. Probably the better ones do. Each chord change has a different sound, there aren't "good" or "bad" ones. Experience and knowledge of theory can help you predict what sounds different chords changes will have. – Todd Wilcox Dec 11 '17 at 19:02
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    Eriek, are you asking within the context of composing a new song? – jdjazz Dec 12 '17 at 0:26
  • @jdjazz Yes mostly, and improvising. Thank you! – Eriek Dec 12 '17 at 0:42
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Basic premise for jazzers jamming is to take a solid set of chords. Such as those from a standard. Take Autumn Leaves. The chords are generally speaking the same, in the same order each time it's played. So there is no need to be thinking which chord could or might come next - it's decreed within the song. Therefore, the choice is narrowed down to which scale notes could be used over that chord, and the following ones. Purely adding a 9th or 6th et al, is not what I'm thinking about here.

It's a different (and more difficult) job to re-harmonise a tune in terms of which chords are used. I'm actually doing that at the moment with Summertime in a small jazz ensemble, and it's taxing in that it still needs the bare bones to remain, otherwise it morphs into a completely different tune, unrecognisable as Summertime. So even in this case, there needs to be some structure from original, and to an extent, it constricts things rather than gives open licence, but once a (slightly) different chord sequence is decided upon, the choice of scales to use over it is somewhat predetermined.

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