Treatise On Harmony -

: He was the first to formalize that a chord like is the same entity as

The treatise is divided into four distinct books that move from abstract math to practical performance: Treatise on Harmony

: Explores the physics of sound, focusing on string ratios, intervals, and the derivation of chords from a single "source" sound. : He was the first to formalize that

: He established the "natural" relationship between chords, particularly the movement between the tonic and the dominant , which remains the backbone of most Western music today. Structural Breakdown Availability and Modern Use Treatise on Harmony (Dover

: Focuses on the practical art of playing from a figured bass on instruments like the harpsichord or organ. Availability and Modern Use Treatise on Harmony (Dover Books On Music: Analysis)

. Before this, theorists viewed these as entirely different intervals above a bass note.