Why Schubert's music holds us in thrall

What is it about Schubert that makes him so fascinating? The world of early 19th-century Vienna that moulded him, evoked with such charm in his waltzes and part-songs, is totally remote from us.

Yet his music speaks with a special, urgent tone. It's as if it were somehow meant for us, and the two centuries' gap between then and now simply doesn't matter.

You could say the same of Beethoven, the other great Viennese composer of the era. But there's a vital difference. Beethoven's ethical fervour and fierce objectivity address us in our public selves. It's music full of struggle, vaulting energy and heroic aspiration, designed for concert halls and big spaces.

Schubert's music could be dramatic and heroic too, as works like his last so-called "Great" Symphony prove. But he often speaks to the solitary within us, in a way that seems to venture close to the edges of human experience.

Perhaps that's why he's the favourite composer of so many novelists, film directors and thinkers. His song-cycles have been turned into mini-dramas and films, above all Winterreise ("Winter's Journey"). These adaptations picture the solitary traveller in a state of existential isolation, as if Schubert were anticipating the world of Unamuno or Beckett (surely it's no accident that he was Beckett's favourite composer).

Schubert's music is often evoked in works by fiercely modernist composers, as if the extremity of his emotional states echoes something in their own world-view. The philosopher Wittgenstein thought Schubert's C major String Quintet was "superhuman" music, and quite simply the greatest piece of music ever written.

Over a nine-day period starting tomorrow (Saturday), radio listeners will have the chance to roam undistracted through Schubert's immense expressive world, as BBC Radio 3 is clearing its schedules to present every note the composer wrote. It's a staggering output, which is hardly rivalled by any other creative artist. In a mere 31 years, Schubert produced more than a thousand works in every genre: piano music, chamber music, operas, dances by the score, church music. And above all there are the nearly 600 songs or Lieder, a genre that he more or less invented.

This total immersion is bound to alter one's view of a composer, in ways one can't predict. But my hunch is that, rather than emphasising Schubert's oddity, it will bring out his normality.

Schubert was gregarious, friendly, aware of his own worth, argumentative, and much given to falling in love - just like the friends he argued with. He liked nothing more than a vigorous walk in the Vienna hills to a local hostelry, or a gathering to try out his latest songs or piano duets. He liked his pipe, and he liked a drink even more. One friend tells the story of how Schubert disgraced himself by attending a party at a grand house, and getting so drunk he had to be put to bed. Much of the music expresses a straightforward happiness in existence.

And yet it was Schubert himself who expressed the view that music is never truly happy, and there is a tinge of heartbreak even in those pieces that are ostensibly jolly. This reflects the other, dark side of existence, which Schubert knew only too well. By 1823, when he was 26, he was aware of the fact that syphilis had claimed him, and what that would mean in terms of physical decline and early death.

"I feel myself to be the most unhappy and wretched creature in the world," he wrote in a letter of 1824. "Each night, on retiring to bed, I hope I may not wake again, and each morning only recalls yesterday's grief."

Described thus, Schubert's grief sounds conventional, even a touch maudlin. But in his music this intuition of mortality takes on a terrifying force. In his final string quartet there's an outcry that seems to tear a hole in the music's fabric; for a moment it stops making grammatical sense. Beethoven never ventured anything like this, nor any other composer until we reach the expressionist works of Arnold Schoenberg.

The other side of that intuition - an awareness of life's fragile fleeting beauty - is what gives Schubert's music its heartbreaking poignancy, expressed often in the simplest terms. The mysterious opening of the "Unfinished" Symphony sets a mood of anxiety and impending disaster. Yet all it takes is one note on the horn, a deft harmonic turn, and suddenly sunlight breaks through the clouds.

The slow movement of the A major Piano Sonata has another typically Schubertian trait - a moment where the harmony rocks between two distant chords, and we're left suspended in a blissful state, away from the world's troubles. You find such things even in Schubert's modest little waltzes, and in a way these are the most mysterious moments of all. They reveal the possibility of transcendence lurking in the everyday.

'The Spirit of Schubert' runs from Saturday until March 31 on BBC Radio 3