7.3. Directed Harmonic Relationships

A relation rule accepts a directed pair of modal states. It may preserve a root or mode, move a root by an interval or circle-of-fifths step, move between specific modes, or combine several alternatives.

The General Purpose profile prioritizes four useful corners: same or +5-semitone root movement crossed with same or next-mode movement. It then accepts Parallel and Steady Brightening as lower-priority fallbacks through phrygian → aeolian → dorian → Mixolydian → Ionian → Lydian without wrapping. Parallel and Steady Darkening follow last through that sequence in reverse, giving constrained libraries another chance to form a complete Mix.

These names describe harmonic policy, not an automatic emotional arc. Library coverage, track arrangement, and the available graph determine what a complete Mix actually becomes.