If Schoenberg had freed the composer from the tradition, John Cage (USA, 1912), a pupil of Henry Cowell, freed the composition from the composer. Cage blurred the distinction between what is music and what is not music. First, he promoted silence, altered instruments (1940), sounds of nature (1941), found sounds (1951), the very movements of the performer (1952), the collage of random noises (1952), and even the background noise of the auditorium (1952) to the status of music, preferring the narrow range of percussion instruments while pioneering electronic music in Imaginary Landscape no.1 (1939), and composing Sonatas and Interludes (1948) for "prepared piano", a technique that paradoxically scaled down the piano's expressive power and basically turned it into a polyrhythmic percussion instrument (the equivalent of a percussion ensemble), an expedient later transposed to the String Quartet (1950). Not content, in 1951 Cage also introduced indeterminacy and randomness in the process of making music, as demonstrated in the Piano Concerto (1958). Thus Cage's music could be the random ("aleatoric") outcome of "events" that were foreign to traditional music making (in which the only events are the musicians playing their instruments based on the composer's score). His score for ASLSP (1985) simply stated "to be played as slow as possible", which, when performed on an organ, could lead to infinite duration (a performance in a church of the German town of Halberstadt began in September 2001 and will last until 2640). Like in Zen meditation, Cage's pieces highlighted a higher dimension, which was not to be found in the minute details of the piece but in the experience of it. While Cage did not attempt to bridge the gap between performer and listener, he downplayed the composer (who specifies only the actions, not the music itself), increased the degrees of freedom of the performer (who produce the music), and, indirectly, demanded that the listener began to "listen" in a different way, more integrated with the act of making music. In 1952 he organized an event at Black Mountain College around his Theater Piece No 1 with dancer Merce Cunningham, pianist David Tudor and painter Robert Rauschenberg; and in 1958 Allan Kaprow gave these events a name: "happening". Cage extended the scope of Dadaism beyond mere provocation and turned it into a new perception of the artistic event; which is, after all, just that: an event. He removed both form and content from art, and left only the process. But, more than an artist, Cage was a creator of genres. He wrote the history of avantgarde genres for the following 50 years (and counting), even though he didn't give it any masterpiece.

Another pioneer of the caliber of Cage, Boris Blacher (Germany, 1903), penned the abstract opera Abstrakte Oper 1 (1953), which has no words and no action.

Brion Gysin (Britain, 1916) was the true inventor of the "cut-up" technique made popular by his friend William Burroughs. The two experimented with it while in Paris during the 1950s, Burroughs focusing on fiction while Gyson applied it to just about any art, including "music" (audio cut-up).

The end of World War II marked a new period of aesthetic revolution that built upon the most radical ideas of the previous decades while adopting new technologies that had become available.

John Cage had already composed Imaginary Landscape N.1 for magnetic tape in 1939. When (1946) the city of Damstadt in Germany set up a school for avantgarde composers, the magnetic tape became one of their "instruments".

In 1948 Pierre Schaeffer (France, 1910) created a laboratory in Paris for "musique concrete" (music made of noises, not notes), basically the practical implementation of Luigi Russolo's theories. Pieces such as Symphonie Pour Un Homme Seul (1950) used technology to alter the original ("concrete") sound. The instrument was no longer a piece of the orchestra but a piece of a recording studio. Schaeffer pioneered the use of "found sounds" to compose original music.

Pierre Schaeffer's disciple Pierre Henry (France, 1927), who had already collaborated to the Symphonie Pour Un Homme Seul (1949) and to the opera Orphee' (1953), continued his masters program in a more populistic vein with: Concerto Des Ambiguite' (1950), a noisy dialogue for two pianos that seems reminiscent of French absurdist theater; Le Voyage (1962), a sinister electro-acoustic suite for electronically processed sounds of the orchestra; the Variations Pour une Porte et un Soupir (1963) for found sounds (a door and a sigh); Reine Verte (1963), a theatrical soundtrack for found sounds, sound effects, voices and electronic imitations of popular music (such as Rock Electronique); Messe Pour Le Temp Present (1967), mostly a rock mass that harks back to psychedelic music (with the electrifying Psyche' Rock).

Rune Lindblad (Sweden, 1923) employed damaged film to automatically produce the sounds of Optica 1 (1959).

Joseph Schillinger published "A Mathematical Basis of the Arts" (1949), in which he proposed that popular music could be composed by combining snippets of existing popular music. Basically, he had envisioned "sampling" before the invention of the sampler.

In 1951, Karlheinz Stockhausen joined the school of music at Darmstadt, and began composing "elektronische musik".

In the same year, the French national radio set up a studio to record electronic music in Paris, and the West Deutsche Radio opened a similar studio in Cologne (the NWDR).

In 1952, across the ocean, electronic engineers Harry Olson and Herbert Belar built the first synthesizer at RCA's Princeton Laboratories, the "Mark I".

It was just a matter of time before new genres based on electronic instruments appeared. Musica su Due Dimensioni (1957) by Bruno Maderna (Italy, 1920) was the first "electro-acoustic" composition, mixing traditional instruments and electronic tape. A computer composed the Illiac Suite (1957), using software created by Lejaren Hiller.

At the other end of the spectrum, Schoenberg's ambition to invent a new logic of musical composition was adopted by composers who tried to "serialize" (prescribe) the entire dynamics of a piece (not only the notes). Elliott Carter (USA, 1908) conceived atonality as a disjointed choir of voices in the Quartet 1 (1951) and the Quartet 2 (1959). The instruments simulated actors in a drama, and counterpoint became a dialogue between different characters. In his Double Concerto (1961) the two solo instruments are basically playing two different concertos. The culmination of this program was the hectic and effervescent rhetoric of the Concerto for orchestra (1969) and of the Symphony for Three Orchestras (1977). Milton Babbitt (USA, 1916) indulged in the intricate mechanisms of his String Quartet 2 (1954) and Ensembles For Synthesizer (1964). George Perle (USA, 1915) followed suit with the Quartet 5 (1960). Pierre Boulez (France, 1925) achieved the rigorous science of Structures (1951) and delved into the disorienting percussive patterns of Le Marteau Sans Maitre (1954) before turning to an aleatory format inspired by the poet Mallarme' with Sonata piano 3 (1957) and Pli Selon Pli (1962). Jean Barraque (France, 1928) with La Mort de Virgil (1968), and Karel Goeyvaerts (Belgium, 1923) with Litanies (1982) were other serialists.

Electronic music owed much to Karlheinz Stockhausen (Germany, 1928), who contributed to popularize all the main techniques. The first major artifacts of "tape music" (invented a few years earlier by Edgar Varese) were his experiments with electronics and voice, namely Gesang der Junglinge (1956), and with electronics and "samples", namely Hymnen (1967). His serialist orchestral work Gruppen (1957), on the other hand, was concerned with spatial location and movement of sound, another influential theme of the avantgarde. Returning to electronic music, Stockhausen pioneered two more subgenres: "electro-acoustic" chamber music (1958), which mixes tape music and traditional instruments; and "live electronic music" (1964) which uses the electronic instrument "like" a traditional instrument (save that, obviously, the electronic instrument can play the sounds of all instruments as well as sounds that no acoustic instrument can play).

Concrete music was pursued by Luigi Nono (Italy, 1924) in La Fabbrica Illuminata (1964).

Iannis Xenakis (Greece, 1922) ventured beyond serialism and indeterminacy: the complexity and density of labyrinthine scores such as Metastasis (1954) led him to employ mathematics (and, in particular, stochastic methods), for example in the electronic poems Orient Occident (1960) and Kraanerg (1969).

The three revolutionary schools of the time had changed the rules. Cologne (Stockhausen) introduced purely electronic music. New York (Cage) introduced music of gestures not only sounds. Paris (Schaeffer) introduced music of non-musical sounds.

New forms of music quickly proliferated. In 1957, Max Mathews began composing computer music at Bell Laboratories. Edgar Varese inaugurated tape music with Deserts (1954) and premiered his Poeme Electronique (1958) in a special pavilion designed by architect Le Corbusier, where the music was reacting with the environment. In 1958 the Columbia-Princeton studio for avantgarde composers opened in New York, and was featuring an RCA Mark II, the "synthesizer", and the following year Raymond Scott invented the first sequencer, the "Wall of Sound". In 1959 John Cage performed "live electronic music". Morton Subotnick, Terry Riley, Pauline Oliveros and others founded the "Tape Music Center" near San Francisco in 1962. In 1961 Robert Ashley and Gordon Mumma organized Ann Arbor's ONCE festival, entirely devoted to avantgarde music. Together, these events marked the end of avantgarde music as an exclusive of seasoned (and mostly European) composers and the beginning of avantgarde music as a relatively grass-roots (and mostly American) phenomenon. Sure, the composers were still educated at the most prestigious schools of music: but their stance towards composition/performance was moving away from the concert hall and towards the praxis of jazz music. The musicians of this generation tried many (and wildly different) avenues of experimentation, from musique concrete to electro-acoustic synthesis, but they shared a fundamental aesthetic belief in the power of "sound", as opposed to the traditional emphasis on harmony and melody.

Lucia Dlugoszewski (USA, 1925) started out with pieces in the tradition of Pierre SChaeffer's "acousmatic" music, such as Orchestra Structure For The Poetry Of Everyday Sounds (1952), in the tradition of John Cage's prepared piano, such as Archaic Aggregates (1961) for self-built percussions and timbre piano, and in the tradition of Edgar Varese's percussion music, such as Suchness Concerto (1958), but she also perfected a surreal style for chamber music with pieces such as Concert Of Man Rooms And Moving Space (1960) and Tender Theatre Flight Nageire (1978) for brass sextet and non-pitched percussion.

Louis "Moondog" Hardin (USA, 1916) was one of the greatest and most bizarre geniuses of the 20th century. A New York street performer who dressed up like a Viking, he composed string quartets, symphonies and operas, but mainly surreal vignettes for orchestra and home-made instruments. His works encompass everything that was known and a lot of what was still unknown. He virtually invented every single future genre of rock, electronic and world music. For example, the neoclassical quartet Surf Session (1953) borrowed the rhythm of Middle-eastern folk dancing and employed ocean waves.

Hans Otte (Germany, 1926) was perhaps the first visionary of "deep listening" music, music whose emotional core is as distant from the surface as it can be, basically the exact opposite of German romantic/symphonic music. The peaks (or, better, bottoms) of his minimal art were brief piano sonatas in which very little happens, inspired by Eastern calligraphy and philosophy: Das Buch der Klaenge (1982), documented on The Book of Sounds (1992), and Stundenbuch (1998).