It’s telling that Philip Glass was among those spectators who, one evening in May 1961, watched the composer, conceptual artist and all-round enfant terrible La Monte Young draw a straight line across the floorboards of Yoko Ono’s loft space on Chambers Street, Manhattan. Telling, because Young’s Compositions 1961 explored a less-is-more approach to art that would become a defining feature of Glass’s own work. Influenced by Zen Buddhism, the piece comprises of a simple instruction to ‘Draw a straight line and follow it’, not once (as in Young’s previous Composition 1960 #10) but 29 times. In short, it observes the variety of outcomes that arise from a single repeated event. Glass, a young student at Juilliard at the time, was greatly impressed by its performance, but could not have guessed that along with Young, Steve Reich and Terry Riley, he would go down in history as one of the four founding fathers of Minimalism.

Certainly, to hear Glass’s works from the time, you wouldn’t guess that he was on course to become one of Manhattan’s maverick Minimalists. A straight-A student at Juilliard, his early works cater to his tutors’ taste for Americana – compositions in the style of Copland and Schuman. Glass would ground himself rigorously in the principles of Western composition, studying with Milhaud in Aspen and Nadia Boulanger in Paris, but it wasn’t until his discovery of Indian music through a chance collaboration with sitarist Ravi Shankar on the 1966 film score, Chappaqua, that he began to find his own voice. ‘I discovered world music long before we knew what it was,’ recalls Glass. ‘I saw the possibility of using some of the technical procedures of Classical Indian music with Western instruments and making a very different language. It was a way out of the cul-de-sac that Stockhausen and the Serialist composers had created.’

Much ink has been spilled over Glass’s role in the development of Minimal music, not just because it carved out new directions in Western composition but also, perhaps, because he seems to have drawn a straight line directly from Minimalism to the market place, bringing a distinctive brand of repetitive music to a mass audience. Glass’s style is so widely played and imitated, it’s easy to forget that he once made his name in the comparatively esoteric world of contemporary opera, beginning his journey from scraping a living as a plumber and taxi driver to becoming a full-time composer with Einstein on the Beach (1976). He has since composed around 20 operas, eight symphonies, and numerous concertos, but today is better known for his film scores – The Truman Show, Notes on a Scandal and The Hours, and more. ‘The opera was always the popular art form of its day,’ says Glass, ‘so I’ve just moved from one popular art form to another.’

To meet, Glass is affable, with the softly spoken bookishness and slightly dishevelled hair of a Manhattan academic – one with an absolutely assured understanding of his own status as a cultural icon. (‘We’ve talked for nearly an hour,’ he once told me during an interview, ‘you must be important.’) Undoubtedly, this combination of cultural awareness and intellectual curiosity has played a pivotal role in Glass’s ability to surf the Zeitgeist over the years. He has collaborated with some of the leading artists of his time: in music-theatre with Robert Wilson; film with fellow New Yorker Woody Allen; on rock, world and electronic music projects with the likes of David Bowie, Brian Eno, Paul Simon and Aphex Twin. Ironically, his best-seller ’80s album, Glassworks, is almost due now for a retro revival, but at the age of 73, Glass continues to be in vogue: his latest score for Mr Nice, an adaptation of Howard Marks’s memoirs, is released in UK cinemas in October; he’ll premiere an opera about Walt Disney in Europe in 2011.

These are large-scale works attracting sizeable audiences, so what has Glass got to do with Minimalism? In truth, the answer is not much. In fact, Glass himself has tried to divorce himself from the Minimalist label though without much success over the years. Turn back the clock more than half a decade, however, and you begin to see why. In 1967, Glass returned from Paris, via India, to Manhattan. He was, by now, studying Buddhism. Minimalism was in the air. John Cage’s 4'33" (1952) – a piece in which the performer sits at the piano without making a sound – had shown the infinite variety of sounds that emerge during four minutes and 33 seconds of silence; Terry Riley’s In C (1965) had shown the appeal of sharing simple repeated motifs between players; Reich’s West Coast experiments with tape loops – It’s Gonna Rain, Come Out – and Piano Phase for live performers had uncovered the pulsing effects that occur when repeated motifs are moved in and out of phase with one another and La Monte Young – later credited by Brian Eno as being the ‘granddaddy of us all’ – had embarked on a never-ending study of drones.

‘We all ended up in New York at the same time,’ recalls Glass. ‘La Monte was the most radical and the first to venture into this kind of music. He was so much fun because his pieces were so theatrical. Terry was a wonderful pianist, and could improvise on two keyboards for hours. Reich was there with his group, plus John Gibson, Terry Jennings, Meredith Monk and Charlemagne Palestine. Very quickly there was a group of people who were producing a radical type of music that became known as Minimalism.’

Glass was the last of the ‘mighty four’ to embrace a minimalist approach to music, making the transition to a more stripped-down style after renewing contact with his ex-Juilliard classmate Reich. (That Glass has never acknowledged any debt to Reich would spark an ongoing rivalry between them.) Pooling their resources, they formed an ensemble of players who were willing to experiment. And Glass’s works were radical. Take his earliest experiments such as Strung Out (1967), for example: written for solo amplified violin and performed from a manuscript pegged up around the walls, the performance piece comprised of a stream of semiquavers that are strung out over no more than five pitches. The work did exactly what it said on the tin – it jarred.

It was the first of three works in which Glass explored the notion of additive (and subtractive) rhythm that he had learned from his time studying Indian music with Ravi Shankar. Simply put, Glass sets out a pattern of pitches with the same semiquaver values, adds (or subtracts) one note to (or from) the pattern, repeats the new pattern and repeats the process over long periods of time. He would systematically explore the same principle in 1+1 (1968) in which rhythms were tapped out on an amplified tabletop and Two Pages (1968) – a single line for unison electric keyboards and winds in which 107 patterns are repeated an indefinite number of times. ‘Looking back, I’m kind of astonished because it sounds as though the composer knew exactly what to do,’ recalls Glass. ‘It seemed like a completely thought out strategy, yet as far as I remember, I didn’t know what I was doing. I was fumbling in the dark.’

Compared to some of the relaxing mood music from Glass’s film scores that ripple across the airwaves of today’s easy-listening radio playlists, Glass’s early works can be challenging. In his late 1960s pieces such as Music in Fifths (1969) – in which two lines shared between organ and saxophones move rapidly and repeatedly up and down in parallel motion a fifth apart – Music in Contrary Motion (1969) – hectic-sounding repetitions for electric organ – and the four-part Music in Similar Motion (1969), Glass offers no change in dynamics or key, removing all of the traditional signposts that guide us through a piece of classical music. The initial effect is disorienting. But as the mind submits to the overall sense of stasis, hypnotic patterns emerge like shapes from dots on a canvas.

In many ways Glass’s concerts were closer to rock or jazz gigs than to the traditional chamber music recitals of the concert hall. Standardised in the early 1970s, his ensemble comprised of seven musicians playing keyboards and a variety of woodwinds amplified through a mixer. They played at high volumes, and not in the Carnegie Hall, but at student gigs, rock clubs and art galleries. As their following grew, so too did the scale of Glass’s explorations. As early as Music with Changing Parts (1970) – a piece that would influence the music of the young Brian Eno and David Bowie – Glass began to move away from his strictly reductive writing, adding drones and vocal improvisation, combining colourful textures and danceable rhythms played out over long periods of time. Music in Twelve Parts (1974), would contain 12 sections each lasting about 20 minutes each, marking his move away from Minimalism towards his first opera – and the piece that would make his name – Einstein on the Beach.

Glass speaks with an air of nostalgia when looking back on the ’60s. It was an exciting period of change. ‘Two things were appealing: we had our own audiences in SoHo and the critics left us alone,’ he recalls. Until 1973, his Downtown concerts were deemed too radical to review. Left out of the critical spotlight and without any pressure to please, Glass stripped back the conventions of Western music and composed anew. Unlike the repetitive ideas that he would return to time and time again, this level of experimentation and fresh discovery was something he would never repeat. ‘I still think of myself as re-inventing my voice,’ says Glass. ‘The issue is not in finding a voice but getting rid of it. It’s like wearing the same clothes everyday.’

Nick Shave