VII. Motion Categories
Fiber Inversion
Motion along the ℤ₄ fiber. Preserves the pitch-class set. Atomic in E. Perfect pitch-direction correlation: ±12 semitones per step.
Single-Voice Perturbation
One voice moves by one semitone in B; three voices hold. Atomic in B. The fundamental edge of the chord-graph.
Compound Perturbation
Multiple voices move by one semitone each in a single compositional gesture. Distance-2 (2 voices, 2 common tones) or distance-3 (3 voices, 1 common tone). Not atomic — decomposes into sequential single-voice perturbations.
Window Slide
All four voices move, transposing the entire chord. Distance 4 in B. Perfect pitch-direction correlation: ±28 semitones per step. The OTH analogue of key change.
Geodesic Traversal
Motion along a shortest path between two chords in B. Composite motion type — the path determines the sequence of passing chords. Up to 298 distinct geodesics may exist between antipodal chords.