Healthy discord

Despite its now respectable age, modernist music still befuddles listeners and divides audiences.

"It's just a load of random notes! My six-year-old child could have banged that out on a toy piano." Faced with a piece of modernist music, many people feel as confused as when they first saw a later-career Picasso or stumbled across a punctuation-free ee cummings poem. Without the easily recognisable melodies or stirring harmonies that make romantic music so viscerally moving, it's true that scores by such 20th-century greats as Schoenberg or Stravinsky can at first seem perplexing or coldly conceptual. That it can still confuse the uninitiated is remarkable - it has, after all, been around for a very long time.

Stravinsky's stunning score to the ballet Petrushka turns 100 this year, while his raw, riot-inducing Rite of Spring is a venerable 97. Schoenberg's Verklarte Nacht, meanwhile, was already pushing from lush romanticism into spiky atonality 111 years ago, while his groundbreaking atonal opera Pierrot Lunaire has its centenary in 2012. Given that modernism's once shocking newness was easily trumped by far more radical music after the Second World War, surely it's time for classical audiences to embrace it?

It seems not. Despite being of an age when most things become respectable, early 20th-century modernist music remains confined to a relatively small group of aficionados. None of it, for example, has yet made it into the Abu Dhabi Classics season. This is a pity - while it doesn't always fall into a comfortable melodic groove that sets the listener at ease, some of the most striking, hauntingly beautiful music we have was written in the period, pieces whose memory is impossible to shake off despite being rather difficult to hum. And while classical music's move towards atonality from around 1900 onwards is confusing for some, modernist music speaks more vividly of the cultural and political ferment of its time than all the History Channel's hackneyed, newsreel-heavy documentaries put together.

That said, the quintessentially 20th century movement's roots were buried deep in the 19th century. It was Wagner's opera Tristan and Isolde that, in the eyes of traditionalists, came along and ruined everything way back in 1865. With the sad, eerie opening chord of its overture, it tore up the rule book and set western music on a new course. Here is a brief explanation why. In standard musical notation, there are 12 possible notes in each octave. To sound tuneful in a traditional western manner, however, variations of these notes need to be placed in sets of eight to form major or minor scales. Musical phrases in almost all pre-20th century classical music were written using these fixed sets of eight (or "keys") - to put in a note that did not belong in the chosen key would immediately sound jarring.

Occasionally, composers would add intentionally jarring notes - discords - as brief, striking accents, but these would be followed by a quick return to harmony. Wagner's Overture to Tristan, however, broke this rule: its first musical phrase starts with a discord and resolves to another discord without full harmonic order being restored. While this doesn't interrupt the great swelling waves of sound in the beautiful piece (and sounds fairly orthodox to a modern ear attuned to disharmony), it proved to be the thin end of a very thick wedge.

Although Wagner's music remained controversial, the harmonic innovations he introduced steadily crept into common currency. With the Frenchman Debussy breaking away from strict tonality and reflecting the influence of East Asian music in his compositions, a sense that there might be valid alternatives to traditional western key signatures slowly gained credence. It wasn't until the great Austrian provocateur Schoenberg, however, that music rejected key signatures altogether and moved into complete atonality. Schoenberg started his career as a late romantic, his work showing the influence of Mahler and Wagner, but he came to feel that this tradition's possibilities had been exhausted. Seeking to find a more liberated, abstract way to create music, Schoenberg ultimately rejected key signatures and frequently caused shock and dismay, a fact that seemed to cause him great pleasure.

But even as the listening public rebelled, other rising composers such as Stravinsky and Bartok followed his lead. If anything, they were even more controversial - the Paris premier of Stravinsky's Rite of Spring in 1913 caused riots in the auditorium, with the audience coming to blows over the score's thrilling but brutal accompaniment to a ballet of human sacrifice. The riots themselves are well documented; what happened next, less so. Despite its rocky premiere, the Rite of Spring was a considerable success, with audiences noticing that despite its occasionally harsh sounds (which went on to influence a hundred horror film scores), the piece was dazzling, familiarly melodic in places - and almost catchy.

But while audiences slowly took atonal modernism on board, Schoenberg himself sensed that complete freedom from restraint wasn't necessarily a good idea. Attempting to anchor his atonal music in a more rigorous framework, he developed the 12-tone technique in the 1920s. This arguably rather arbitrary system imposed an ordering principle: in 12-tone music, every note of an octave must be used within a musical phrase before any single note is repeated. While it might seem like a potential blind alley, Schoenberg's innovation provided a much-needed framework for young composers wary of the old rules but still feeling rudderless.

Modernism wasn't just about rewriting the rule book, however. It was also about tapping into traditions that had been ignored or looked down upon in order to breathe life back into "serious" music. Jazz, East Asian and folk traditions were all important components of the modernist mix. Despite the shock of its first night audience, Stravinsky's Rite of Spring clearly shows the influence of old Russian folk songs.

Bartok more than any of his contemporaries immersed himself in folk music, travelling across Hungary, Transylvania and even to North Africa to record folk songs sung by villagers, often incorporating them directly into his own work. While these tunes are transfigured into something rich and strange, the earthy vibrancy of folk is still a potent part of his work, its physicality undercutting the notion that modernism is strictly for eggheads.

Schoenberg's once mentioned daydream of a future where "milkmen will whistle my tunes like Puccini" seems as far off as it ever was. But in a world that has seen such raw experimenters as John Cage and Karlheinz Stockhausen - not to mention the everyday onslaught of electronic dance music - it's time more people learnt how great the music of his period could be. Expecting an alienating exchange between music boffins, many new listeners are taken aback at how heart-stoppingly beautiful modernist music can be. If you're interested in exploring it yourself, here are four pieces that make a good starting point.

This incredible piece by Schoenberg is effectively split down the middle between the 19th and 20th centuries. The first two sections still sound like exquisite if slightly harmonically skewed examples of late romanticism. Then in the third movement, a single soprano voice breaks in, taking the piece into a totally new area that rejects tonal melody but still ravishes the listener with its sharp, moonlit sadness.

The final movement possesses no key signature at all - a fact that caused cries of outrage at its first performance. While back then the quartet might have sounded harsh and bizarre, its powerful emotional expressiveness is more striking today - Schoenberg was reeling from the shock of his wife's infidelity at the time, and devoted the piece to her. Its innovations now long familiar, in hindsight what remains is an impression of richly sensuous tenderness and heartbreak.

The power of Igor Stravinsky's sung ballet to shock and dazzle is every bit as great as his more famous Rite of Spring. Influenced by Russian folk music's harsh, keening voices and irregular rhythms, the piece is incredibly gutsy and alive, its thumping physical kick blowing any assumptions about "cerebral" modernism out of the water. Originally written for Diaghilev's Ballets Russes, the piece's ritualistic, rather bleak portrait of Russian peasant marriage (its French title means "the wedding") melds folksiness with a hammering accompaniment of four pianos and massed percussion. It's hardly easy listening but full of urgency and infectious excitement, though unfortunately its extreme difficulty means it's only rarely performed.

Jarring and lyrical by turns, Alban Berg's stunning, lurid opera brings to life the cultural buzz and social confusion of interwar Germany brilliantly. Based on two controversial plays by Frank Wedekind, the opera follows the Lulu of the title, a chaos-inducing but not entirely unsympathetic femme fatale onto whom the opera's characters project their destructive desires. While the seedy plot is gripping (Jack the Ripper even turns up at the end), the music is complex and varied. It frequently uses Schoenberg's 12-tone technique, but often shows a romantic richness in its string harmonies, interwoven interestingly with snatches of thumping piano, tom tom drums and military brass.

Proof that modernist music can be intensely soulful, this masterpiece was written by the ageing Bartok when he was living in exile in New York. Not strictly atonal, it shows the influence of both Baroque music (the only other well-known unaccompanied violin sonatas are by Bach) and Hungarian folk. It's a phenomenally difficult piece -Yehudi Menuhin, who commissioned the piece, successfully petitioned Bartok to simplify some passages - but it never loses itself in empty virtuosity, shot through as it is with a bittersweet passion that lingers long after the piece has ended.