The Rise of Functional Tonality: From Modes to Keys

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A motet by Palestrina and a trio sonata by Corelli are separated by about a century, and the difference between them is not a matter of ornament. In the motet, harmony is what happens while four or five independent lines are doing something else. In the sonata, two upper lines move above a bass that decides what the harmony is at every moment, and a player at a keyboard fills in the rest. That change in the division of labour is the birth of tonal harmony, and it is visible in the notation long before anyone wrote a theory of it.

#A texture in which the bass decides

Sixteenth-century polyphony is written in partbooks, one voice per book, and each line is conceived as a melody with its own shape and its own cadences. The vertical sonorities that pass by are consequences of the lines, not the subject of the composition. In that world a chord has no root in any practical sense, because nothing in the music asks the question. The lowest sounding voice is simply the voice that happens to be lowest.

Once a composer writes a single melody singing above a single bass line, the bass becomes the harmonic ground. The top voice carries the tune, the bass carries the foundation, and everything between is accompaniment. This is also where inversion becomes a working idea rather than an abstraction: the same chord can sit above different notes in the bass, and the player recognises it as the same chord because the intervals above the bass change while the identity does not.

#Monody, the seconda pratica and the keyboard under the bass

The intellectual pressure for the change came from Florence. Vincenzo Galilei’s Dialogo della musica antica et della moderna of 1581 argued that modern counterpoint had buried the text under its own ingenuity, and the circle around Bardi’s camerata set out to recover what they believed was a Greek union of words and music. The result, within twenty years, was opera: Peri’s Euridice in 1600, Monteverdi’s Orfeo in 1607. In both, the essential texture is a voice and a bass, and the harmony is supplied by a continuo player reading figures.

Monteverdi’s fifth book of madrigals, published in 1605, adds a continuo part to a genre that had done without one, and the quarrel that followed is as instructive as the music. Giovanni Maria Artusi attacked the harmonic liberties of the moderns in 1600, and Monteverdi’s defence, the appeal to a seconda pratica in which the text governs what the rules permit, is the first clear statement that the older contrapuntal rules were one style among several rather than a law of nature.

The practical driver behind all of this is easy to miss: someone had to play the chords, and to do that the chords had to be written down. Lodovico Viadana’s Cento concerti ecclesiastici of 1602 is the standard early example of church music printed with a figured bass part for organ, and within a generation the continuo part is standard equipment from the church to the chamber to the opera house. Once harmony is notated as figures under a bass, the harmonic content of a passage is an explicit object that a composer can plan and a theorist can describe.

#From twelve modes to two keys

The older system organised pitch by mode. Eight church modes, four authentic and four plagal, each with a final and a characteristic range, and the theory of the period treats them as different species of melody with different expressive characters. Two developments narrowed that to the major and minor scales.

The first was slow and took most of the fifteenth century: the third and the sixth were gradually accepted as consonances rather than tolerated dissonances, which is what makes a chord of root, third and fifth possible in the first place. Fifteenth-century treatises such as Tinctoris’s Liber de arte contrapuncti of 1477 catalogue consonances in a way that already includes them.

The second was theoretical and happened in a single generation. Heinrich Glarean’s Dodecachordon of 1547 argued for twelve modes rather than eight, adding Ionian and Aeolian, the modes that correspond to what later centuries called major and minor. Gioseffo Zarlino’s Le istitutioni harmoniche of 1558 worked the major third into a systematic account of harmony. By the later seventeenth century, practical theory had two keys rather than twelve modes, and the modes survived in the church tones, in transposed performance practice, and in vernacular music that never needed the theory.

The reason the change stuck is structural. When the chord is the unit of harmony, the third is the note that decides the chord’s quality, and there are two qualities. Transposition then becomes trivial: a key is a set of relationships, not a fixed set of pitches, so the same piece can be moved to another key without becoming another piece.

#Rameau names the fundamental bass

Jean-Philippe Rameau’s Traité de l’harmonie of 1722 gave the practice a theory. Its central idea is the fundamental bass, the root of each chord, which is not necessarily the sounding bass note: an inverted chord has a sounding bass that is not its fundamental. Once the fundamental is distinguished from the bass, chord identity is stable across inversions, and a piece can be described as a sequence of roots with bass notes underneath them.

Rameau also argued that harmony derives from the harmonic series of a sounding string, which was a strong claim that has been argued about ever since. What survived is the descriptive apparatus rather than the physics: roots, inversions, and the tendency of roots to move by fifth. The teaching tradition built on it turned the description into a drill, above all in the Neapolitan conservatories of the eighteenth century, where a student harmonised a scale either in the standard formula of the rule of the octave or against a partimento bass that left the chords unwritten. A modern harmony exercise descending from a figured or unfigured bass is a descendant of that pedagogy.

#The cadence becomes the engine of a key

What makes a key a key is not the notes available but the cadence that keeps confirming a centre. In modal polyphony, cadences come in several types and land on different finals, and the leading tone that gives a tonal cadence its direction was often not written at all: performers supplied it as musica ficta, an accidental understood rather than notated.

By the Baroque the raised leading tone is in the notation, and the cadential motion of a root falling a fifth into the tonic, with the leading tone rising to the tonic in an upper voice, is the standard punctuation of the style. That is the shift from mode to key in one sentence: the leading tone makes a final into a centre.

The G sharp is what defines the key. Without it the chord is a minor seventh chord on E, and the arrival on A would be an ending rather than a confirmation. With it, the chord is a dominant seventh and the A is a tonic.

The same motion in C major. The cadence transposes, which is exactly what modal finals do not do, and it is why a piece can move to another key, confirm it by cadence, and be understood to have modulated. The cadence types themselves are a vocabulary built on this single motion.

#Function is a nineteenth-century description

The vocabulary most people learn first, tonic, subdominant and dominant with their substitutions, is younger than the music it describes. Hugo Riemann’s function theory, set out in the 1890s, grouped chords by the role they play rather than by their root, and it is the source of the T, S and D labels. Heinrich Schenker’s later account, culminating in Der freie Satz of 1935, reduced the same repertoire to voice leading and a background structure, and treated the surface chords as elaborations of it. Both are nineteenth- and twentieth-century attempts to describe a practice that had been running for two hundred years.

The disagreement matters for anyone analysing old music, because the labels will almost always fit something. A Palestrina cadence can be given a Roman numeral, and a Josquin passage can be assigned functions, and the analysis will look plausible while describing the wrong thing: in that repertoire the vertical sonorities are consequences of the lines, the cadences have different weights and different kinds, and the piece is organised by mode rather than by a tonic that everything pulls towards.

The practical consequence is a reading habit. For music written before 1600, follow the lines, note where each voice cadences, and identify the final the piece keeps returning to; for music written after, follow the bass, mark the cadences that confirm the key, and label a function only where you can hear the role it plays. The chord-function model describes the second repertoire extremely well and the first one poorly, and the date of the change is the reason.

Questions

Did functional harmony exist before 1600?

The chords existed, and cadences existed, but they were byproducts of independent lines rather than the organising principle of a piece. Roman numerals and function labels often fit a Palestrina motet, and using them misdescribes how the music actually moves.

Who codified chord function?

Rameau's Traité de l'harmonie of 1722 established the fundamental bass and made a chord's identity independent of its bass note. The three functions as they are taught today, tonic, subdominant and dominant, come from Hugo Riemann's function theory of the 1890s.