Tonality is a theoretical system of pitch organization in Western music based on a definite tonal center that came to be known as the “tonic.” Tonality is both hierarchical and relational in that certain pitches with a community of pitch classes possess greater and lesser degrees of importance in determining the central “key.” Tonality is referred to as being “diatonic” music (from the Greek, dia tonikos—literally “through tones”) due to the scalar structures (ascending and descending sequence of pitches) in which give rise to two basic modalities called major and minor.
Tonality as a musical syntax evolved from the monophonic music of the early Christian church although this type of tonal centricity can also be found in varying degrees in the folk music of Asia and the Middle East. The scales that these cultures utilized, which were based on different intervallic structures than the scales that evolved in Europe, (specifically, the intervallic division of the octave) became the genesis of the particular modalities of those regions and cultures.
As composers in Europe during the Middle-Ages and the Renaissance began to write music with greater linear complexity (polyphony) the natural by-product of this process was a vertical alignment of tones that possessed very definite harmonic textures. The evolution of harmonic syntax though the fifteenth and sixteenth centuries, along with the experiments in tuning and interval modification (temperament) led to the development of very specific harmonic theories which in turn gave rise to a codified system of major/minor and sharp/flat key centers. The diatonic major and minor scales, based on a specific sequence of major and minor intervals, along with the use of triads (three pitches sounding simultaneously) became the fundamental properties of tonality, which in turn provided an aural base or "home" key, and was to become known as the tonic.
As the theoretical codification of harmony was abstracted from usage in the fifteenth and sixteenth centuries, a specific system of terminology was developed that identified triads that were based on each of the seven pitches of the major and minor scales in the tonal spectrum:
These "scale degrees" (and their attendant Roman Numerals) are the basis from which any harmonic analysis of a composition written in accordance with the principles of tonality can be ascertained. The chord quality (major or minor) of each triad differs depending on the modality of the key center (major key or minor key.)
French composer and organist Jean-Phillipe Rameau (1683-1764) published his Traité de l'harmonie in 1722 and this theoretical discourse remains one of the most important documents on the subject of tonality. Unlike theoreticians before him, Rameau looked to science, specifically the overtone series, as a way to explain the nature of musical phenomena in relation to the theoretical properties of tonality. Influenced by the theories of Descartes and Sauveur, Rameau posited that there was a fundamental relationship between the harmonic principles in tonal music and the physics of sound (acoustics.)
He asserted that chords (triads) where the primary elements in music as opposed to melody or themes. His ideas regarding functional harmony, specifically the cadential relationship between the tonic, sub-dominant and dominant chords within a particular key center, became the underlying principles of what would become known as “the common practice” in musical composition in the Western music for three hundred years. The cadential relationship between tonic and dominant triads (as well as secondary dominants) is elemental to the tonal syntax.
Johann Sebastian Bach’s (1685-1750) seminal composition, The Well-Tempered Clavier, which was composed in the same year that Rameau published his Traité de l'harmoni, is the composition in which it could be said that the full establishment of tonal principles were initially manifested. In that composition Bach composed a set of works in all major and minor keys thereby exhibiting the veracity of tonality both theoretically and aesthetically. It should be noted that Equal Temperament did not become a fully accepted method of tuning until after World War I. Bach's tuning/temperament in 1722 was not the tuning that eventually came to be used in Equal Temperament in the early part of the twentieth century.
Although there have been numerous variations and modifications of tonal principles (chromaticism, pan-diatonicism, extended-tonality, e.g.) tonality remains an extremely viable mode of musical expression. Jazz and Western popular music continue to utilize the basic principles of cadential tonic/dominant harmony that are typified in the music of Bach, Beethoven, Brahms and Mahler.
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