Initially, the effect of equal temperament on Western music was probably beneficial. Composers obtained the ability to modulate freely and to build complex chromatic harmonies that had been impossible under the meantone system. As a result, abstract instrumental music flourished as never before, yielding what is generally considered the "golden age" of Western music. Like a plant stimulated by chemical fertilizers and growth hormones, music based on equal temperament grew rapidly and luxuriously for a short period—then collapsed. If equal temperament played a prominent role in stimulating the growth of harmonic music in the common-practice era, it played an equally large part in its rapid demise as a vital compositional style. Twelve-tone equal temperament is a limited and closed system. Once you have modulated around the so-called circle of fifths, through its twelve major and twelve minor keys, and once you have stacked up every combination of tones that can reasonably be considered a chord, there is nowhere left to go in search of new resources.
This is essentially where Western composers found themselves at the beginning of the twentieth century. Everything that could be done with the equally tempered scale and the principles of tonal harmony had been tried, and the system was breaking down. This situation led many composers to the erroneous conclusion that consonance, tonality, and even pitch had been exhausted as organizing principles. What was really exhausted was merely the very limited resources of the tempered scale. By substituting twelve equally spaced tones for a vast universe of subtle intervallic relationships, the composers and theorists of the eighteenth and nineteenth centuries effectively painted Western music into a corner from which it has not, as yet, extricated itself. Twentieth century composers have tried in vain to invent or discover new organizing principles as powerful as the common-practice tonal system. Instead, they have created a variety of essentially arbitrary systems, which, although they may seem reasonable in the minds of their creators, fail to take into account the capabilities and limitations of the human auditory system. These systems have resulted in music that the great majority of the population find incomprehensible and unlistenable.
Given that equal temperament had only been in general use for about 150 years at the time, it may seem strange that so few of the composers of the early twentieth century recognized that the cure for music's ills lay, at least in part, in the replacement of its inadequate tuning system. (Some theorists and composers did, in fact, advocate the adoption of new, microtonal tuning systems, but most of these proposals were for microtonal equal temperaments, such as quarter tones, third tones, sixth tones, eighth tones, etc., which merely divided the existing twelve tone scale into smaller, arbitrary intervals, and which made no improvement in the tuning of Western music's most fundamental intervals.) However, despite its fairly recent origin, equal temperament had already become quite deeply entrenched in Western musical thought and practice. There were several reasons for this. One was the industrial revolution. The nineteenth century saw the redesign and standardization of many instruments, particularly the orchestral woodwinds and brass. Strictly speaking, only fixed-pitch instruments (the piano, organ, harp, tuned percussion, and fretted strings) require temperament, the others being sufficiently flexible as to adjust pitch as musical context requires. Nevertheless, brass and woodwind instruments were also standardized to play a chromatic scale such that the "centers" of their pitches corresponded as closely as possible to the pitches of twelve-tone equal temperament. Another reason for the persistence of equal temperament was the repertory of the common-practice period. The previous 150 years had witnessed the development of the orchestra as we know it, along with its repertory, and the concert system that supported it. It had also seen the evolution of the piano, the preeminent equally tempered instrument, as the predominant instrument for both solo performance and accompaniment, and as the most important tool in musical education. The orchestra, the piano, and their players, trained to perform the works of eighteenth and nineteenth century composers, were the resources that turn-of-the-century composers had to use if they wished to have their music performed. And all of these resources were dedicated to music that assumed equal temperament. It was little wonder, then, that few composers were willing to challenge this massive establishment in order to work in some new, untested tuning system.
Although most composers were sufficiently intimidated by the weight of eighteenth and nineteenth century musical practice, fortunately a few were not. The first twentieth century composer to make a serious commitment to Just Intonation and the person primarily responsible for the revival of Just Intonation as a viable musical resource was Harry Partch (1901–1974), the iconoclastic American composer, theorist, instrument builder, dramatist, and musical polemicist. When Partch began his compositional career, no one, to the best of my knowledge, was making music in Just Intonation. Beginning with tentative experiments in the mid-1920's, and continuing over a span of 50 years, Partch developed a system of Just Intonation with 43 tones to the octave, built a large ensemble of predominantly stringed and percussion instruments to play in this tuning system, composed and staged six major musical theater pieces, along with numerous lesser works, and produced and distributed his own records. In 1947, Partch published his Genesis of a Music, an account of his musical theories, instruments, and compositions that became the bible for subsequent generations of Just Intonation composers.
Whereas in previous centuries the goal of most intonational theorists was to find the ideal or most practical tuning for a culturally predominant scale, such as a major, minor, or chromatic scale, the approach of twentieth century composers and theorists working with Just Intonation, as exemplified by Partch, has been quite different. The goal of these artists has been, in most cases, to discover or create a tuning or tunings that best served their own particular musical goals, whether for a single composition or for a lifetime's work, rather than one that could serve the needs of the culture as a whole.
From when he began work in the mid-1920's until the mid-1950's, Partch was the only composer in the United States doing significant work in Just Intonation. In the 50's, Partch was joined by Lou Harrison (1917–2003) and Ben Johnston (b. 1926). Harrison first learned about Just Intonation from Partch's Genesis of a Music. He composed his first major work in Just Intonation, Four Strict Songs for Eight Baritones and Orchestra, in 1954. Although, unlike Partch, he did not work exclusively in Just Intonation, Harrison wrote a large body of work in various just tunings. He is probably best known for the creation, in conjunction with his companion William Colvig, of a number of justly tuned American gamelan (Indonesian-style tuned percussion ensembles), and for the body of music he composed for this medium, but he also composed just music for a great variety of instrumental and vocal ensembles, often mixing elements from European and Asian musical traditions. Through his teaching at San Jose State University and Mills College in California and his extensive lecturing, he introduced many younger composers to Just Intonation.
Ben Johnston discovered the possibility of Just Intonation early in life, when he attended a lecture on Helmholtz at age eleven. Later, he, like Harrison, discovered Partch's Genesis of a Music. Johnston contacted Partch and for a six month period in 1950 was his student and apprentice in the remote California coastal town of Gualala. Johnston began composing seriously in Just Intonation in 1959. Unlike Partch and Harrison, Johnston's work in Just Intonation employs mainly Western musical forms and instrumental combinations. His earlier work, through the early 1970's, generally combines extended microtonal Just Intonation with serial techniques. His later work tends to be simpler and more tonal, but still uses serialism at least occasionally. Johnston's works include eight string quartets in Just Intonation, and numerous vocal and chamber ensemble pieces. He is also the inventor of a system of notation for extended Just Intonation that is used in this primer.