I am trying to describe it ... It was a tone in which all tones resounded while at the same time it contained all the silence. (Psychologist Silvia Ostertag during a masterclass of cellist Pablo Casals).

[1] In Cage and Noise, I investigate the way in which John Cage deconstructs the borders between music and noise. More familiar, perhaps, is the way in which Cage has concerned himself with the relation between music and silence. 'We should listen to the silence with the same attention that we give to the sounds',  writes Cage. His point of departure is the simple, but crucial observation that the materials of music consist of sounds and silence; that to compose is to articulate these two. The only parameter of sound that is shared by silence is duration. 'If you consider that sound is characterized by its pitch, its loudness, its timbre, and its duration, and that silence that is the opposite and, therefore, the necessary partner of sound, is characterized only by its duration, you will be drawn to the conclusion that, of the four characteristics of the material of music, duration, that is, time length, is the most fundamental. Silence cannot be heard in terms of pitch or harmony: it is heard in terms of time length', Cage states in a lecture on Satie (Kostelanetz, p.81). From this, Cage finds that the underlying structure of music can no longer be based on harmony and tonality (Beethoven), or on the twelve-tone system (Schönberg). The underlying structure of music is rhythmic. 'There can be no right making of music that does not structure itself from the very roots of sound and silence - lengths of time' (Cage in Kostelanetz, p.81-2).

[2] A central role of duration. A central role of the concept of silence. During the course of Cage's life, his thoughts on silence have undergone some changes, including the way it appears throughout his compositions. In his article, 'So etwas wie Stille gibt es nicht' ['There is no such thing as silence'], Eric de Visscher distinguishes three stages that may serve to mark out Cage's developing thoughts on silence. The stages are a structural notion of silence, a spatial notion, and silence as the absence of any intention or purposiveness (cf. Visscher, p.48-54). These three notions will be elaborated upon below.
(One comment: Unlike De Visscher, I do not regard these stages as a chronological development, but as an analytical tool. In any given time period, Cage may work in various ways. For example, he may drop some of his ideas while reactivating others from the past. There is no linear progression; it is more like layers overlapping one another.)

[3] A structural notion of silence.
At first, Cage conceives of silence in a traditional way, as the absence of sound, or as minimal sound activity. Already, however, silence is not just a negativity to Cage. The attention to silence aids in uncovering musical structure since this can only be determined by duration (see above). By assigning the primacy of the musical parameters to duration, Cage not only opens music to silence, but to all sounds of any quality or pitch. Music becomes an empty (silent?) concept from which any type of sound may emerge. Silence acquires an important role: only through silence can the musical material adopt many types of sounds.
A reversal takes place. A reversal in (thinking on) music. A reversal in the traditional hierarchy in music where silence is secondary and subordinate to sound (cf. Visscher in Nauck, p.8). Silence becomes an absolute prerequisite for the introduction of all sounds to the musical domain. This new (concept of) music originates from silence. A reversal for sure. However, this structural notion of silence still leaves Cage bound to a relatively classical attitude as it rests on the definition of silence as the absence of sound. The relation between sound and silence is horizontal, that is to say, they take turns in succession, thereby excluding each other. The musical structure rests on their order and mutual exclusion (cf. Visscher, p.49).

[4] A spatial notion of silence.
Cage's 'Lecture on Nothing', a reading from 1950, signals a shift in his thinking on silence. He realizes that the important role of silence regarding musical structure does not yet establish a full recognition of its positive qualities. Cage wants to avoid approaching silence from a negative point of view, i.e., as absence of sound. At the beginning of 'Lecture on Nothing', he attempts to arrive at a different relationship towards silence. 'What we require is silence; but what silence requires is that I go on talking ... But now there are silences and the words make help make the silences ... We need not fear the silences, we may love them' (Cage, 1961, p.109-10). Silence is no longer the absence of sounds; silence itself consists of sounds. Silence begets sounds. Chiasm. Reversibility. Through the intertwining of silence and sound, their mutual penetrability now becomes appreciated. Each retains a part of its antipode; each requires the other as its frame. The necessary interdependency between sound and silence relates to two principal aspects: silence is not only the precondition for sound - this means that silence contains sound - every sound in turn harbors silence as well. (According to Martin Zenck, the 'Lecture on Nothing' points out that the words of spoken language by which the silence is demarcated are in fact the precondition for silence.) The latter principle manifests itself especially in compositions that are on the outer limits of audibility, such as Waiting (Play music) (cf. Cage and Noise). In this 'silent piece', silence does not disappear when a tone resounds, rather, it continuously resonates along with the tones. Here, a vertical conception of silence comes into play. Sound and silence develop in a parallel way without mutual exclusion; the one is always already present in the other (cf. Visscher, p.49-50).

[5] A spatial concept of silence. Silence as a space that is always already pregnant with sounds. And vice-versa! The relation between silence and sound becomes more complex. To Cage, it no longer suffices to state that silence and sound are mutually dependent in order to exist, or that sound emerges from silence. Cage reverses this idea: silence resounds in sounds. Silence becomes more prominent when traces of silence in sounds are detected. 'Music already enjoys inaudibility (silence)', Cage writes (Kostenaletz, p.116). After his 'Lecture on Nothing', Cage's thoughts on silence and sound go through a shift that is embodied in his 'Lecture on Something'. (The opposition of silence-sound, together with oppositions such as nothing-something, death-life, law-freedom, etc., form an entire chain of apparent oppositions in Cage's universe that can no longer be thought as oppositions. As such, they are objects of a strategy of deconstruction in music.)
'It is nothing that goes on and on without beginning middle or meaning or ending. Something is always starting and stopping, rising and falling. The nothing that goes on is what Feldman speaks of when he speaks of being submerged in silence. The acceptance of death is the source of all life. So that listening to this music one takes as a springboard the first sound that comes along; the first something springs into nothing and out of that nothing arises the next something; etc. like an alternating current. Not one sound fears the silence that extinguishes it. And no silence exists that is not pregnant with sound' (Cage, 1961, p.135). Silence is (not) nothing; it is no longer the absence of sound. It consists of all the ambient sounds that make up a musical space, a space of which the borders cannot always be clearly defined. Silence is the space in which sounds occur. Sound and silence are simultaneously present with one constantly carrying traces of the other. Cage now no longer reverses the hierarchical opposition (where sound or music is primary and silence is secondary). Instead, he undermines the opposition as a whole. Sound and silence become two versions of a generalized arche-silence with the result that they both acquire a different status.

[6] As long as Cage holds onto the structural notion of silence he has no need to give up the idea of silence as emptiness. However, his merging of silence and life brings about a dispersion of the difference between silence and (ambient) sounds. This was not just a theoretical thought construct. Evidence of this can be found in Cage's recollection of an experience in a soundproof chamber at Harvard University. 'For, when, after convincing oneself ignorantly that sound has, as its clearly defined opposite, silence, that since duration is the only characteristic of sound that is measurable in terms of silence, therefore any valid structure involving sounds and silences should be based, not as occidentally traditional, on frequency, but rightly on duration, one enters an anechoic chamber, as silent as technologically possible in 1951, to discover that one hears two sounds of one's own unintentional making (nerve's systematic operation, blood's circulation), the situation one is clearly in is not objective (sound-silence), but rather subjective (sounds only), those intended and those others (so-called silence) not intended' (Cage, 1961, p.13-4). Silence cannot be the absence of sound: 'There is no such thing as silence', Cage concludes (Cage, 1961, p.191). Silence consists of all existing sounds (silence as life) that surround us (silence as spatial dimension) (cf.Music, Noise, Silence and Sound). This ultimately opens the musical world to the entire world of sounds, including non-musical sounds (cf. Visscher, p.51). By doing so, Cage also undermines the distinction between central and peripheral tone properties that were natural for centuries in European music. Intensity and timbre are no longer subordinate to the pitch and duration of the tone. They no longer add 'color' or 'spice' to these so-called central properties; rather, they are to be regarded as independent and equal parameters. The traditional hierarchy between the secondary tone properties (expression and coloratura) and the primary, structural parameters (tone duration and pitch) is now implicitly subject to reconsideration.

[7] Silent music. Like Waiting (Play music). This composition does not contradict the properties of silence. The sounds retain the 'reverberation of nothingness' from which they originate. Obviously, this silence is not to be understood as ordinary silence. Silence can be full, all encompassing, indeed, it may even be loud. During the first sixteen bars of Waiting (Play music) , a world of sounds unfolds that was excluded from the world of music for the longest time. Since Cage cannot and will not manipulate these sounds, it is always unclear what these sounds will be. The tenuous piano sounds that join these ambient sounds from bar 17 on will not drown them out. The 'silence' remains audible throughout the piano part and is inextricably integrated in the composition. Silence and (musical) sound are both present at the same time. One is not reduced to the other. There is no hierarchical relation either. The sounds of the piano engage into a dialogue with their environment; they join the already present sounds respectfully, that is, without too much disturbance, and modestly retreat before the piece reaches its close. A double silence. A first silence frames the musical piece (a silence framed by the concept of music in turn). A silence around music, but only experienced through music. A second silence is not a background silence, but converges with the musical piece. Silence on silence. Silence in music.

[8] Silence as the absence of any intention.
After describing his experience at Harvard, Cage writes that the difference between sound and silence cannot be a property of an object or a situation since sound is ubiquitous at all times. Therefore, a division between the two rests on a distinction between intended and non-intended sounds. In his 1958 reading, 'Composition as Process', a summary of his ideas on silence, Cage returns to this matter. 'Formerly, silence was the time lapse between sounds, useful towards a variety of ends, among them that of tasteful arrangement, where by separating two sounds or two groups of sounds their differences or relationships might receive emphasis; or that of expressivity, where silences in a musical discourse might provide pause or punctuation; or again, that of architecture, where the introduction or interruption of silence might give definition either to a predetermined structure or to an organically developing one. Where none of these or other goals are present, silence becomes something else - not silence at all, but sounds, the ambient sounds. The nature of these is unpredictable and changing. These sounds (which are called silence only because they do not form part of a musical intention) may be depended upon to exist. The world teems with them, and is, in fact, at no point free of them' (Cage, 1961, p.22-3, my italics). Silence no longer coincides with itself, but transforms into unpredictable and changing ambient sounds from which one cannot escape. These sounds are called 'silence' because they are non-intentional. It is the presence or absence of an intention, meaning, or purpose that distinguishes musical sounds from silence. Silence is not merely the absence of sounds; something is called silence when there is no apparent connection to the intentions that produce these sounds. (This means that there is no essential distinction between silent silence and loud silence according to Cage. They both lack intention.)
Out of respect for these sounds, Cage takes care that his compositions do not disrupt this state of non-intentionality or silence. He argues in favor of 'a composing of sounds within a universe predicated upon the sounds themselves rather than upon the mind that can envisage their becoming into being' (Cage, 1961, p.27-8). Musical sounds should be in harmony with the sounds of the outside world. Silence becomes a perceivable presence (i.e., the sounds that surround us) and composing is about finding sounds that respect this silence. 'When I write a piece, I try to write it in such a way that it won't interrupt this other piece which is already going on' (Cage in Duckworth, p.15). Cage writes his music on the sounds that always already surround it. Arche-silence. Not a word, not a concept that can be defined. Arche-silence is the play of differences (among music, silence, and sound). Arche-silence makes possible this play of differences.