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.

The opt-in Tritone rules use the corresponding mode relationships with a +6-semitone root move. Two tritone root moves return to the original pitch class, so Tritone Intervals alternates between two roots while keeping the mode fixed. Same-mode tritone scales share two of seven pitch classes; the actual overlapping phrases still decide whether a pairing sounds convincing. Audition each directed pairing and save successful transitions as Gems.

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.