From Hexachords to Tonality: The Evolution of Western Musical Organization

The tonal system, as codified in the Common Practice Period (c. 1650–1900), stands as a culmination of
centuries of theoretical and practical developments in Western music. Among its foundational stages
was the hexachordal system developed in the Middle Ages, which served as the organizing principle of
pitch and solmization for nearly half a millennium. Understanding this system and its transformation into
tonality involves tracing the shifting conceptions of pitch, scale, and function across theoretical,
pedagogical, and compositional traditions.

This essay explores the hexachordal framework of early music, its theoretical underpinnings, functional
use, and eventual integration into the modal and tonal systems that followed. The story is not one of
replacement, but rather one of evolution, as old paradigms gave rise to new conceptions of musical
space.

I. The Hexachord System: Origins and Function

A. Guidonian Solmization

The hexachord system was introduced by Guido of Arezzo (c. 990–1050), a Benedictine monk and
theorist who revolutionized musical pedagogy in the 11th century. To facilitate sight-singing and learning
of chant, Guido devised a system based on six-note segments called hexachords, each following the
intervallic pattern:

T–T–S–T–T

This corresponds to:

Ut – Re – Mi – Fa – Sol – La

For example:

Natural Hexachord: C–D–E–F–G–A

Soft Hexachord: F–G–A–B♭–C–D

These three overlapping hexachords allowed singers to navigate the pitch gamut (from Γ (Gamma) to E')
using mutation—switching from one hexachord to another at common pitches. The whole system was
anchored to the gamut, a pitch system of 20 notes derived from combining these hexachords.

Importantly, this system:

Lacked a true octave structure

Emphasized stepwise intervals and relative solmization

Focused on teaching chant and avoiding tritones (notably between B and F)

The system’s purpose was pedagogical, not compositional—it helped singers internalize intervals and
perform orally transmitted chants accurately.

B. Effects on Composition and Perception

Though the hexachord system was not a compositional grammar in itself, it shaped how music was
conceptualized and notated. It emphasized:

Linear melodic motion

Avoidance of mi–fa (half-step) tritones

Early polyphony, such as in Notre Dame organum and Ars Antiqua motets, was still rooted in chant-
derived modal frameworks, but the solmization system underpinned how singers and theorists related to
pitch material.

II. From Hexachords to Modes

A. Modal Theory (8–12 Modes)

By the 13th–14th centuries, theoretical models shifted from hexachordal pedagogy to modal
classification. The church modes—eight, then later twelve—provided a broader structural organization
of melodic and tonal space. These were based on the final (usually D, E, F, or G), the range (ambitus), and
reciting tones.

While hexachords governed local pitch behavior (especially solmization), modes governed global melodic
behavior. Importantly, hexachordal and modal systems coexisted, with the hexachord system serving as
the practical means of navigating modal space.

For example:

The Dorian mode (D–D, final on D) would mostly use the natural hexachord for C–D–E–F–G–A

Mutation was needed to access pitches outside a given hexachord

Though modes began to suggest tonal centers, they were not yet keys in the modern sense—
functionality was still melodic, not harmonic.

B. Contrapuntal Expansion and Hexachord Limitations

As polyphony developed in the 14th and 15th centuries (Ars Nova, Ars Subtilior, Burgundian School), the
limits of the hexachord system became apparent:
Composers needed access to chromatic inflections (musica ficta)

Voices began using independent modal or tonal centers

Functional harmonies emerged from contrapuntal voice-leading

The increasing harmonic awareness required more flexible pitch systems than hexachordal solmization
could easily accommodate. Still, hexachords remained part of pedagogical training well into the
Renaissance.

III. Transition Toward Tonality

A. Emergence of Cadential Patterns

By the early 16th century, composers like Josquin des Prez and Palestrina were using cadences that
increasingly resembled tonal functions:

Authentic cadences (V–I implications)

Leading tones (musica ficta sharpening 7th degrees)

Third-based harmony (triadic writing)

Although Renaissance theory still described music in modal terms, the practical treatment of pitch
suggested a gravitation toward tonic–dominant polarity. The pervasive use of plagal and authentic
cadences, and the presence of clear modal finals, foreshadowed tonal thinking.

B. Chromaticism and Tonal Tension

Extensive chromaticism

Ambiguous modes

Emphasis on vertical sonority

These developments undermined strict modal coherence and set the stage for a new system where
chords, not modes, would become the organizing unit.

IV. The Rise of Tonality

A. From Modes to Major/Minor

The transition to tonality crystallized in the early Baroque. Composers began to favor major and minor
scales (Ionian and Aeolian modes) over the full modal gamut. This simplification coincided with:

The development of functional harmony

Use of figured bass and continuo realization

Emergence of key signatures and circle of fifths

By the time of Monteverdi and Heinrich Schütz, the tonal system was taking shape. By the time of Bach,
it was fully codified.

B. Functional Harmony and Key Relationships

Tonic, dominant, subdominant functions

Voice-leading norms (resolution of leading tones, treatment of dissonance)

Cadential formulas (perfect authentic cadences, deceptive cadences)

Keys were now hierarchically related, and modulation became an expressive tool. This represented a
fundamental shift: from horizontal/modal thinking to vertical/tonal thinking.

V. Pedagogical Shift: From Hexachord to Scale Degree Theory

The pedagogical language of music shifted as well:

Solmization gave way to scale degrees (1–7)

Mutation was abandoned for key-based instruction

The movable-do system became simplified to match major/minor tonality

Hexachordal solmization persisted in some forms (e.g., tonic sol-fa), but the underlying conceptual
framework changed from relative interval navigation to key-centered functional harmony.

Conclusion

The evolution from hexachordal organization to tonality was not a sudden revolution but a centuries-
long transformation of musical thought. Originating as a practical tool for chanting, the hexachord
system formed the mental scaffolding for pitch organization in medieval and Renaissance music. As
compositional demands grew—especially in polyphony, chromaticism, and harmonic structure—the
hexachord gave way to modal systems, which in turn yielded to the functional major/minor tonality of
the Baroque and Classical eras.

The story of hexachords is thus not a dead end, but a crucial evolutionary step, embodying the
transitional logic from medieval pedagogy to modern tonal organization. By understanding its structure
and function, we gain deeper insight into the continuity of Western music theory, and the rich
complexity of its development.