The Nature Of The Transition From The Renaissance Modes To The Major And Minor Keys Of The High Baroque Has Long Remained One Of Musicology's Great Unanswered Questions. The System Glarean Proposed In His 1547 Dodecachordon Comprised Twelve Modes At Two Transposition Levels; The Scheme J.s. Bach Used To Order The Well-tempered Clavier In 1722 Featured Two Modes At Twelve Transposition Levels. What Took Place In Between? This Book, The Product Of Deep Engagement With The Corpus Of Western Music Theory, Presents A Model To Clarify The Factors Of This Complex Shift. The Essence Of This Model Is The Dynamic Interplay Of Three Historical-conceptual Layers Arising Successively In The Middle Ages, Renaissance, And Baroque, Each Layer Continuing Once Introduced. Medieval Theorists Conceived Mode Along A Continuum Between Tune And Scale. Renaissance Theorists Extended Mode From Plainchant To Polyphony, Applying It To Such Parameters As Cadential Hierarchies And Contrapuntal Imitation. Early Baroque Mapping Of Vocal Modality Onto The Keyboard Catalyzed A Transformation From Diatonic Gamut To Chromatic Keyboard As Background Pitch System, With A Corresponding Change From Ladder To Circle As The Dominant Model For Tonal Space, Culminating In The Circle Of Fifths. Illustrating The Rise Of Tonal Circularity Are Dozens Of Diagrams From Historical Treatises. Especially Revealing Are Volvelles, Rotating Paper Wheels That Highlight Music's Ties To Cartography And Cosmography At The Dawn Of The Scientific Revolution. This Study Fittingly Culminates With Exploration Of Tonal Labyrinths, Pieces That Modulate Around The Circle Of Fifths-- Provided By Publisher.