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1a      Major-mode systems with common-practice harmonic and voice-leading behaviors. May be inflected by minor-mode or chromatic mixture.
1b   Minor-mode systems with common-practice harmonic and voice-leading behaviors. May be inflected by major-mode or chromatic mixture.
2 Diatonic modal systems with common-practice voice-leading but sometimes not with common-practice harmonic behaviors.
3a Major-mode systems, or modal systems, with mixture from modal scale degrees. Common-practice harmonic and voice-leading behaviors would be common but not necessary.
3b Major-mode systems with progressive structures. Common-practice harmonic and voice-leading behaviors would be typical at lower, but not higher, levels.
4 Blues-based rock: minor-pentatonic-inflected major-mode systems. Common-practice harmonic and voice-leading behaviors not always emphasized at the surface, but may be articulated at deeper levels and/or in accompaniment.
5 Triad-doubled or power-chord minor-pentatonic systems unique to rock styles: I - bIII - IV - V - bVII. Common-practice harmonic and even voice-leading behaviors often irrelevant on the surface.
6a Chromatically inflected triad-doubled or power-chord doubled pentatonic systems of early metal. Common-practice harmonic and voice-leading behaviors often irrelevant on the surface.
6b Chromatically related scale degrees with little dependence upon pentatonic basis. Common-practice harmonic and voice-leading behaviors often irrelevant at deeper levels as well as surface.