Henry Cowell in the context of Graphic notation (music)

Indeterminacy is a composing approach in which some aspects of a musical work are left open to chance or to the interpreter's free choice. John Cage, a pioneer of indeterminacy, defined it as "the ability of a piece to be performed in substantially different ways".

The earliest significant use of music indeterminacy features is found in many of the compositions of American composer Charles Ives in the early 20th century. Henry Cowell adopted Ives's ideas during the 1930s, in works allowing players to arrange the fragments of music in a number of different possible sequences. Beginning in the early 1950s, the term came to refer to the (mostly American) movement which grew up around Cage. This group included the other members of the New York School. In Europe, following the introduction of the expression "aleatory music" by Werner Meyer-Eppler, the French composer Pierre Boulez was largely responsible for popularizing the term.

A tone cluster is a musical chord comprising at least three adjacent tones in a scale. Prototypical tone clusters are based on the chromatic scale and are separated by semitones. For instance, three adjacent piano keys (such as C, C♯, and D) struck simultaneously produce a tone cluster. Variants of the tone cluster include chords comprising adjacent tones separated diatonically, pentatonically, or microtonally. On the piano, such clusters often involve the simultaneous striking of neighboring white or black keys.

The early years of the twentieth century saw tone clusters elevated to central roles in pioneering works by ragtime artists Jelly Roll Morton and Scott Joplin. In the 1910s, two classical avant-gardists, composer-pianists Leo Ornstein and Henry Cowell, were recognized as making the first extensive explorations of the tone cluster. During the same period, Charles Ives employed them in several compositions that were not publicly performed until the late 1920s or 1930s, as did Béla Bartók in the latter decade. Since the mid-20th century, they have prominently featured in the work of composers such as Lou Harrison, Giacinto Scelsi, Alfred Schnittke and Karlheinz Stockhausen, and later Eric Whitacre. Tone clusters also play a significant role in the work of free jazz musicians such as Cecil Taylor, Matthew Shipp, and Kevin Kastning.

John Milton Cage Jr. (September 5, 1912 – August 12, 1992) was an American composer and music theorist. A pioneer of indeterminacy in music, electroacoustic music, and non-standard use of musical instruments, Cage was one of the leading figures of the post-war avant-garde. Critics have lauded him as one of the most influential composers of the 20th century. He was also instrumental in the development of modern dance, mostly through his association with choreographer Merce Cunningham, who was also Cage's romantic partner for most of their lives.

Cage's teachers included Henry Cowell (1933) and Arnold Schoenberg (1933–35), both known for their radical innovations in music, but Cage's major influences lay in various East and South Asian cultures. Through his studies of Indian philosophy and Zen Buddhism in the late 1940s, Cage came to the idea of aleatoric or chance-controlled music, which he started composing in 1951. The I Ching, an ancient Chinese classic text and decision-making tool, became Cage's standard composition tool for the rest of his life. In a 1957 lecture, "Experimental Music", he described music as "a purposeless play" which is "an affirmation of life – not an attempt to bring order out of chaos nor to suggest improvements in creation, but simply a way of waking up to the very life we're living".

Charles Edward Ives (/aɪvz/; October 20, 1874 – May 19, 1954) was an American modernist composer, actuary and businessman. Ives was among the earliest renowned American composers to achieve recognition on a global scale. His music was largely ignored during his early career, and many of his works went unperformed for many years. Later in life, the quality of his music was publicly recognized through the efforts of contemporaries like Henry Cowell and Lou Harrison, and he came to be regarded as an "American original". He was also among the first composers to engage in a systematic program of experimental music, with musical techniques including polytonality, polyrhythm, tone clusters, aleatory elements, and quarter tones. His experimentation foreshadowed many musical innovations that were later more widely adopted during the 20th century. Hence, he is often regarded as the leading American composer of art music of the 20th century.

Sources of Ives's tonal imagery included hymn tunes and traditional songs; he also incorporated melodies of the town band at holiday parade, the fiddlers at Saturday night dances, patriotic songs, sentimental parlor ballads, and the melodies of Stephen Foster.

String piano is a term coined by American composer-theorist Henry Cowell (1897–1965) to collectively describe pianistic extended techniques in which sound is produced by direct manipulation of the strings, instead of or in addition to striking the piano's keys. Pioneered by Cowell in the 1920s, such techniques are now often called upon in the works of avant-garde classical music composers.

George Gershwin (/ˈɡɜːrʃ.wɪn/; born Jacob Gershwine; September 26, 1898 – July 11, 1937) was an American composer and pianist whose compositions spanned jazz, popular and classical music. Among his best-known works are the songs "Swanee" (1919) and "Fascinating Rhythm" (1924), the orchestral compositions Rhapsody in Blue (1924) and An American in Paris (1928), the jazz standards "Embraceable You" (1928) and "I Got Rhythm" (1930) and the opera Porgy and Bess (1935), which included the hit "Summertime". His Of Thee I Sing (1931) was the first musical to win the Pulitzer Prize for Drama.

Gershwin studied piano under Charles Hambitzer and composition with Rubin Goldmark, Henry Cowell, and Joseph Brody. He began his career as a song plugger but soon started composing Broadway theater works with his brother Ira Gershwin and with Buddy DeSylva. He moved to Paris, intending to study with Nadia Boulanger, but she refused him, afraid that rigorous classical study would ruin his jazz-influenced style; Maurice Ravel voiced similar objections when Gershwin inquired about studying with him. He subsequently composed An American in Paris, returned to New York City and wrote Porgy and Bess with Ira and DuBose Heyward. Initially a commercial failure, it came to be considered one of the most important American operas of the 20th century and an American cultural classic.

Lou Silver Harrison (May 14, 1917 – February 2, 2003) was an American composer, music critic, music theorist, painter, and creator of unique musical instruments. Harrison initially wrote in a dissonant, ultramodernist style similar to his former teacher and contemporary, Henry Cowell, but later moved toward incorporating elements of non-Western cultures into his work. Notable examples include a number of pieces written for Javanese style gamelan instruments, inspired after his introduction to noted gamelan musician Kanjeng Notoprojo. Harrison would create his own musical ensembles and instruments with his partner, William Colvig, who are now both considered founders of the American gamelan movement and world music; along with composers Harry Partch and Claude Vivier, and ethnomusicologist Colin McPhee.

The majority of Harrison's works and custom instruments are written for just intonation rather than the more widespread equal temperament, making him one of the most prominent composers to have experimented with microtones. He was also one of the first composers to have written in the international language Esperanto, and among the first to incorporate strong themes of homosexuality in his music.

Sidney Robertson Cowell (born Sidney William Hawkins; June 2, 1903 – February 23, 1995) was an American ethnomusicologist, collector of folk songs, and the wife of the composer Henry Cowell.