Physics: Harmonic function: Tonic (I, vi), Subdominant (IV, ii), Dominant (V, vii°) — each group has characteristic tension-resolution behavior. Voice leading rule: minimize motion, avoid parallel 5ths/8ths (counterpoint rules from Fux 1725). ii–V–I: dominant preparation via subdominant — the cornerstone of jazz harmony. Tritone substitution: replace V7 with ♭II7 (share guide tones B and F), a standard jazz reharmonization. Rameau (1722) Traité de l'harmonie: established that chords are primary, with melody derived from root + stacked thirds.