Except that what has just been heard is already part of the work - with every seeming random clash and inconsequentiality notated down to the last detail. In his programme note for the world premiere, which the Arditti Quartet will be giving in Antwerp on 19 September, Carter writes: "One of the fascinations of attending rehearsals of chamber music, when excellent players try out fragments of what they will later play in the ensemble - then play it and then stop abruptly to discuss how to improve it - is that the pattern is so similar to our inner experience of forming, ordering, focusing and bringing to fruition and then dismissing our feelings and ideas."
So the new work's 20-minute span evolves as a sequence of six movements - often dominated by a single texture, as in the dry-leaf scurryings of the central Presto or the bizarre pizzicati of the concluding Capriccioso - but introduced and linked by passages of composed disorder as the performers metaphorically discuss what they have just played and try out what they are about to. After the initial surprise, it seems a structural idea so natural to chamber music, the wonder is that nobody thought of it before.
Nobody, that is, except Carter himself. For the concern to derive the basic material of compositions from the playing situation, and the very characters of the various instruments, goes back a long way in his career; likewise the notion that, rather than following received forms, works ought to be allowed to evolve freely, by analogy with the interplay of thoughts and feelings in our inner consciousness, or the impinging of outer impressions and events in our lives. And this openness of attitude springs, in turn, from a seminal experience of modernism in Carter's schooldays, almost seven decades ago.
Granted, openness hardly seems the salient quality of modernism in retrospect; the more doctrinaire later stages of the movement at Darmstadt after the Second World War have seen to that. What is easy to forget is that the origins of musical modernism before the First World War were far more individualistic and intuitive - born of a spontaneous desire by a variety of quite separate composers to break down the old conventions and let in the fresh air. Schoenberg, Bartok and Stravinsky were not on the phone to one another; only between the wars did they and their followers begin to codify the new sounds and techniques they had discovered, and to swap notes at international festivals of contemporary music.
Born in New York on 11 December 1908, Carter was, of course, a quarter of a century or more younger than the original modern masters. And, in any case, he was expected to go into his family's lace-importing business. But Carter's parents had reckoned without the lure of New York itself, which, in the aftermath of the First World War, was about to enter on one of its culturally most adventurous, not to say colourful, eras.
Even today, internationally honoured master and formidable polymath that he is, Carter cannot suppress a kind of schoolboyish glee as he recounts how he heard Mayakovsky declaiming his poetry, watched the young George Gershwin rippling through the first performance of his Rhapsody in Blue, and once even saw Houdini in the flesh. But what really excited him were the performances of the breakthrough masterpieces of modernism which conductors such as Leopold Stokowski and Serge Koussevitzky were bringing to New York for the first time. "I can't give a date," Carter recalls, "but certainly The Rite of Spring was a very important and meaningful work." He also followed avidly the lively new American avant-garde led by Edgard Varese and later the young Aaron Copland - with the backstage encouragement of that most awesome of American musical pioneers, Charles Ives.
While still in high school, Carter had the good fortune to be befriended by Ives, who took him to concerts and encouraged his first attempts at composition. Carter also seems to have picked up an interest in ethnic and oriental music surprisingly early and eventually his knowledge and understanding of Western tradition would extend back to the remotest middle ages. But he is adamant that, as a teenager, he liked only contemporary music: "I couldn't stand hearing Beethoven or Bach or Wagner back then." He was a natural modernist from the start.
This was to cause problems. The still Brahms-centred music department at Harvard bored him stiff - though he did profit from a few months of post-graduate lessons with Gustav Holst, who, he says, "was mildly scandalised by the music I was then writing - wrong-note music like Hindemith". And by the time he got to Paris in 1932 to study with Nadia Boulanger for three years, he had reluctantly come to feel that the more expressionist excesses of modernism which had thrilled his youth were "part of the madness that had led to Hitler".
Back in New Deal America after 1935, he duly strove to fulfil the more populist programme of such older colleagues as Copland. Early works such as his First Symphony (1942) and Holiday Overture (1944) drew upon what might be called the New England pastoral idiom, and upon jazz. "At that time I was a real jazz fan. There were nightclubs on West 52nd Street where Art Tatum and other pianists I liked used to play. All these impressions flowed back into the First Symphony and the Holiday Overture." Maybe these pieces, well-made though they are, somehow lack Copland's inimitable "gift to be simple". But that is because they barely manage to contain what would soon burst out as Carter's equally inimitable gift to be complex.
Finally reverting, after the Second World War, to his original modernist impulses, Carter embarked upon a radical expansion of his musical language towards the "focused freedom" of expression he increasingly envisaged. In some ways, this period of exploration paralleled what the younger generation of Boulez and Stockhausen were trying to achieve in post-war Europe. But Carter remained truer to the empirical spirit of earlier modernism. He was never prepared to trap himself in the rigid schemes of serialism, for instance; on the other hand, the younger Europeans never achieved remotely the swirling momentum of Carter's middle-period pieces, in which he found ways of evolving entire movements from the interplay of constantly fluctuating tempi.
Between the appearance of the massive, multi-layered First String Quartet (1951), which established Carter's international reputation, and the tumultuous Concerto for Orchestra (1969) inspired by a vision of America swept by great winds of change, Carter strove to combine the utmost differentiation of his individual players with the utmost integration of his overall forms.
"I do not want to write the kind of music that just marches on and marches off," he would say. "I want it to seem like a crowd of people, or like waves on the sea." The effort often cost him thousands of pages of sketches; the results remain exceedingly difficult to perform. But when they do come off, Carter's works of the 1950s and 1960s exert an expressive power, a physical punch like few others of the period.
If Carter had retired from composing around the age of 70, he would continue to be thought of as a late developer whose fame rested upon a relatively small number of large-scale scores. Maybe he even thought of himself that way at the time, for in 1980 he abandoned his long-term publisher and, when asked how his future works would be promoted, was heard to shrug, "Well, I've probably only got half a dozen things left to write anyway."
How to explain, then, that the last 15 years have brought forth a flood of some 30 new scores, including a number of elaborate orchestral works, two full-scale concertos, two string quartets and a skein of delectably volatile shorter pieces for small groups or single instruments? Doubtless finding a willing new publisher is part of it. Carter also concedes: "In the past few years I've eliminated some of the circumstances that were taking a lot of time away from composition. I no longer teach, I don't give lectures, and many of the pieces I write now are shorter." But the main impression is of an artist who has spent decades arduously mastering the means to realise his visions suddenly finding he can work with a new immediacy: an Indian Summer comparable only with such late-flowering masters as Rameau and Janacek.
No doubt there is also an element of racing against time. Last winter, Carter was seriously ill with a form of pneumonia that put him on oxygen for five weeks. Yet by June he was back on the international circuit, travelling to the Aldeburgh Festival to hear the first performance of a major new song-cycle on words by his compatriot John Hollander. And before flying to Belgium for the Fifth Quartet, he will be at the Proms on Wednesday for the world premiere of his latest orchestral score, Adagio tenebroso - all this, in the 87th year of a composer who persists in looking and carrying on like a man 20 years younger.
The Adagio - a darkly upwelling processional of slowly evolving lines and chords composed, uniquely in Carter's mature music, against an unvarying beat - is part of his most daring creative wager of all. When he composed his kaleidoscopic Partita for the Chicago Symphony Orchestra in 1993, he revealed that it was the first panel of a projected triptych. The Adagio, commissioned by the BBC, is the central panel. Carter, like most composers, is reluctant to talk about works in progress, but the third panel is already underway, begun the very next morning after the completion of the Fifth Quartet. When finished, the triptych will comprise a span of over 50 minutes - the longest structure in Carter's entire output.
From the immensely long perspective of his career, Elliott Carter is wry about the tendency of fashion to go round in circles: "I remember George Antheil, who created a great sensation in the late Twenties with his repetitive music. There was a widespread repetitive-music trend associated with the cinema, dating back to Satie. Now we talk about repetitive music as if it were something new, and I feel as if I'm witnessing a lapse in history and knowledge." Amid the pluralistic inconsequentialities of our post-modern scene, one can only view with something like awe the continuing, purposeful progress of this last of the modern masters.
Andrew Davis conducts the world premiere of Carter's 'Adagio tenebroso' at the Proms: Wednesday 7pm, Royal Albert Hall, Kensington Gore, London SW7 (0171-589 8212), and live on BBC Radio 3Reuse content