For Cage, composition became the art of assembling or defining a set of sounds, and then creating sets of procedures, often involving the use of random numbers derived by methods such as tossing coins or rolling dice. He began to call his methods chance procedures. In contrast to the extreme determinism of serial music, his approach was aleatoric -- leaving parts of the piece up to the performer or to chance.

"It is thus possible to make a musical composition the continuity of which is free of individual taste and memory (psychology) and also of the literature and 'traditions' of the art."

"I believe that by eliminating purpose, what I call awareness increases. Therefore, my purpose is to remove purpose."

"If you develop an ear for sounds that are musical it is like developing an ego. You begin to refuse sounds that are not musical and that way cut yourself off from a good deal of experience."

Cage sought unexpected juxtapositions of events to create an environment that transcended the will or expectation of the composer, that would bring about new and interesting events that would not have been conceived otherwise.

"What actually happened was that when things happened that were not in line with my views as to what would be pleasing, I discovered that they altered my awareness. That is to say, I saw that things which I didn't think would be pleasing were in fact pleasing, and so my views gradually changed from particular ideas as to what would be pleasing, toward no ideas as to what would be pleasing."

Christian Wolff wrote: "Cage used chance as a way of liberation, both psychological and technical, from self, taste, imagination, musical tradition, and ingrained compositional habits."

Consistent with his earlier compositions, Cage would often create a structure in time first, then fill it with types of sounds. Sonatas and Interludes (1948) was structured into 100 measures, which were subdivided into ten groups of ten measures, which were subdivided into groups with the proportions three-three-two, groups thus being composed of fractional measures. The instrument was a prepared piano containing pieces of rubber, metal screws, and other objects between the piano strings, to create a percussion instrument.

Imaginary Landscape #4 (1951) was for 12 radios, and whatever might be on the air at the time of the performance.

Music of Changes (1951), written for solo piano, was created entirely by coin tosses, which were used to determine various characteristics of each note.

In 1951, Cage and Cunningham toured America. In Denver, where they gave performances and master classes, they met a dance student named Carolyn Brown, whose husband, Earle (1926-2002), was a composer. The Browns soon moved to New York to work with Cage. Cage had formed the Project for Music for Magnetic Tape. He had the goal of creating a library of as many sounds as possible on strips of tape. It was similar in purpose to Schaeffer's goal of codifying a library of recorded sounds, though perhaps Cage was more whimsical about the idea than Schaeffer was.

He worked with Louis and Bebe Barron as engineers to assemble 600 initial sounds. He began to work on Williams Mix, based on a random score and a library of sound elements.

The sounds were classified into six categories:
A -- city sounds
B -- country sounds
C -- electronic sounds
D -- manually produced sounds, including acoustic music
E -- wind-produced sounds, including the human voice
F -- "small" sounds, requiring amplification/processing to be audible Each category was subclassified as
  c -- controlled/predictable
  v -- uncontrolled/unpredictable

Each event in the piece was coded with one of the six main categories, followed by three characters of c or v, which were applied to pitch, timbre, and loudness. So an event coded as Accv would signify a city sound of controlled pitch, controlled timbre and uncontrolled volume. The library was kept in envelopes.

Events were categorized and ordered using the I Ching, the ancient Chinese oracle. The I Ching is used by tossing three coins (or Chinese yarrow sticks) six times, and drawing a line symbol depending on whether the coins are mostly heads, mostly tails, or completely heads or tails. For the Chinese, the resulting hexagrams reflect forces of nature and the universe that are active at that moment, and are used in divination. There are 64 hexagrams. Cage associated the different hexagrams with sound classifications (or silence), eight tracks of tape, duration, plus attack and decay (determined by cutting the tape at a certain angle at one end). Anyone who happened to visit his loft at this time could expect to be given three coins and put to work creating I Ching hexagrams for the score. The score was assembled from these series of random coin tosses. It was graphic, a drawing of lengths and cutting angles of pieces of tape, along with the sound classification of each, picked at random from the appropriate envelope. The piece was assembled by placing the score under a glass plate on a table, and laying the tape on top, "as if it were a dressmaker's pattern" Cage described it. There was no tape player, and they had no idea what the sound would be.

Cage and Earle Brown laid the tape pieces, after which they were attached to splicing tape. When a minute or so of material was assembled, the patchwork was taken to Dick Ranger's studio and copied onto continuous tape. Only then did they actually hear what they had assembled.

At some point in the early 1950s, Cage was invited to visit the acoustics laboratory at Harvard, where he went into an anechoic chamber -- a room that absorbs all sound. Rather than experiencing complete silence, Cage heard two sounds. The engineer explained, "The high one is your nervous system in operation; the low one is your blood in circulation." Cage was delighted to find that silence does not really exist, and wrote, "We need not fear about the future of music."

In 1952, Cage presented a work that was to become a landmark in American music history. 4'33" (1952) consisted of a performer (David Tudor at the premier) sitting on the stage at the piano for four minutes and thirty-three seconds, closing the keyboard lid and opening it again three times to indicate sections of the piece. Frequently misunderstood, the aim of the piece is not to produce silence nor to explore the reactions of the audience. The piece is an environment, and the sounds that occur within that time. The audience was to become aware of ambient and accidental sounds that occurred during that time period. The score states that it may be performed anywhere, with any type of instrument. This represented a new attitude towards the act of listening, and a re-examination of just what music was.

When Williams Mix was completed, Cage and Brown worked on Brown's Octet, which was assembled out of the remaining tape pieces.

Williams Mix and Octet premiered in 1953 at the University of Illinois Arts Festival. They were played on eight monophonic tape decks, each of which was output to a separate loudspeaker. The eight loudspeakers were placed around the audience in an early form of what is now called "surround sound." The concert also featured works by Stockhausen, Boulez, Luening, and Ussachevsky.

Despite their clear differences in methodology, Cage and Stockhausen considered themselves allied creatively. Both considered their philosophies to be outgrowths of Webern's work, although they had taken different creative paths. Cage had this view of their differences:

Stockhausen assumes a responsibility toward the problem of unification of disparate elements...[indeterminacy concerns itself with the] possibility of making music not dependent upon linear continuity.