Tonal harmony

Tonal harmony is the system of chord relationships that organizes much Western music around a central chord, the tonic. It is commonly associated with the common-practice period, from the mid-17th century to the second half of the 19th. Its principles remain widespread in present-day popular and film music.^[1:1] Theorists describe it using harmonic function, the categories of tonic, predominant and dominant chords, and through conventional progressions and cadences that mark the ends of phrases.^[2:1][2:2]

The related term "tonality" is broader and contested. It can name a historical repertoire, the perception of keys and tonics, or a set of features shared by many musical styles.^[3:1][4:1]

History of the concept

Alexandre-Étienne Choron and François-Joseph Fétis introduced the term tonalité in the early 19th century; it first appears in print in a work by Choron and Fayelle published in 1810. They used it to sort ancient and modern music within an evolutionary narrative, and most music theorists regard Fétis as the originator of the concept. In his Histoire générale de la musique (1869), Fétis explicitly linked his concept of tonality to biological racism and white-supremacist thought.^[3:2]

Jason Yust argues that the term has two senses that do not fit together. In one, tonality is a practical, historical category that separates "tonal" from "post-tonal" repertoire, courses and analytical tools. In the other, it is a musical property concerned with the perception of keys and tonics. Yust contends that the combination perpetuates the term's racist origins and that music theory could drop the term without loss.^[3:1]

Harmonic function and the phrase model

Theory textbooks such as Open Music Theory group the chords of a key into three functions:

• Tonic: I (or i in minor), which sounds stable.
• Predominant: chords such as IV and ii, which lead away from the tonic toward the dominant.
• Dominant: V and vii°, which create a sense of urgency to resolve to the tonic.

The "phrase model" describes the usual order of these functions. A phrase needs at least tonic and dominant harmonies to have a sense of direction, often includes a predominant before the dominant, and almost always moves from tonic toward dominant rather than in reverse.^[2:1]

Yust describes harmonic function as specific to certain styles: the common practice (roughly 18th- and 19th-century European concert music) and later music that draws on it. In his account it developed in 18th-century Europe to make long-form dramatic instrumental music possible.^[3:3]

Cadences

Cadences are melodic and harmonic patterns that mark the end of a phrase and help establish a key. An authentic cadence ends with the progression V–I. It is "perfect" when both chords are in root position with the tonic note in the top voice, and "imperfect" otherwise. A half cadence ends on V and sounds inconclusive. Perfect authentic cadences are the strongest kind and half cadences the weakest.^[2:2]

Chord progressions and directedness

Moss and colleagues characterize tonal harmony along four dimensions:

• Centricity: a few central chords dominate.
• Referentiality: chords are oriented toward reference points such as the tonic.
• Directedness: some progressions are preferred over their reverse.
• Hierarchy: chords are nested within local keys, which in turn are nested within the key of the whole piece.^[1:1]

A progression from one chord to another is asymmetric if it occurs more often than its reverse. Such statistical regularities are thought to shape listeners' expectations through implicit learning. Root motion by a descending fifth, especially from V to I, is generally regarded as central to tonal harmony. Dissonant chords such as seventh chords and suspensions create specific expectations about which chord comes next.^[1:2]

Tonal harmony is closely tied to voice leading. Dmitri Tymoczko describes Western music as lying at the intersection of harmony, which determines which chords and chord sequences are acceptable, and counterpoint, which connects the notes of successive chords into simultaneous melodies.^[5:1] He argues that the consonant chords of tonal music divide the octave nearly evenly, which lets composers connect them by efficient, independent voice leading.^[5:2]

Empirical and computational study

Moss and colleagues analysed the Annotated Beethoven Corpus, which holds about 28,000 expert chord labels for Beethoven's string quartets. They found that chord frequencies follow a power-law-like distribution, in which a few chords make up much of the data. Tonic and dominant chords alone account for more than 60% of chords in major-key passages and more than 50% in minor-key passages. They also found that progressions are directed in time, and that tonal harmony behaves differently at the level of chords than at the level of keys.^[1:3]

Much research in music cognition, including work by Krumhansl, Temperley and others, treats the distribution of pitch classes in a passage as the defining feature of a key. Pitch-class profiles are a standard tool for automatic key detection. They are often described as "tonal hierarchies" that rank pitch classes into notes outside the scale, scale notes outside the tonic triad, and notes of the tonic triad.^[3:4]

Extensions and limits

Late 19th-century composers often used chains of triads that confound conventional Roman numeral analysis. Neo-Riemannian theory explains such progressions through the common tones the chords share, rather than through their membership in a key.^[6:1]

Tymoczko proposes five features that characterize tonality in a broad sense, among them harmonic consistency and smooth voice leading. In various combinations, he argues, they define an "extended common practice" running from 11th-century polyphony to contemporary jazz. Reviewing the proposal, Julian Hook notes that centricity is the feature that most sharply separates 18th- and 19th-century common practice from the rest of this broader tradition.^[4:1]

In loop-based popular music, competent listeners sometimes hear different notes as the tonic of the same song. Yust argues that, for at least some popular styles, identifying a single tonic is not part of understanding the music.^[3:5]

Wikidata: Q3127530