A third hand up his sleeve?

The fashion for conducting from the keyboard grows and grows. Krystian Zimerman does it with his personal orchestra, Daniel Barenboim does it all over the place, and now veteran keyboard-conductor Murray Perahia is cementing his relationship with the Academy of St Martin-in-the-Fields with an evening of concertos by Bach. Though here, the composer is the thing: after his triumphant performance of the Goldberg Variations, he's now emerging as one of Bach's most oracular representatives on earth.

But when I meet him, the day after he was scheduled to record the Goldbergs in Hanover, he looks pale and shocked. "The recording didn't happen. Someone dropped the Steinway and it smashed. Who dropped it, no one's admitting. But this was the piano on which I've done all my concerts and recordings for the last three years. It had a beautiful singing tone, and the capacity for infinitely subtle nuances. It's catastrophic." He thinks he knows of a possible replacement. "But it has less subtlety, and a bit too much brilliance."

The last evidence we have of the deceased instrument's erstwhile power is Songs Without Words (Sony), on which Perahia juxtaposes Bach-Busoni chorales with Mendelssohn miniatures. Here, his artistry brilliantly disguises Mendelssohn's mediocrity, and with Busoni's arrangements of Bach it takes wing in the most magical way. His interpretations are technically astonishing: how, for example, does he manage to sandwich a sustained slow melody between a busy bass and a skittering top when the three absolutely unbroken lines are several octaves apart? (You almost think he has a third hand up his sleeve.) But these tracks also imply a strong take on the controversies still raging over how Bach should and shouldn't be done.

Perahia is not one of those who regard Busoni's transcriptions as heresy. "When you remember the way Bach changed the sound in his own transcriptions - for example, arranging Vivaldi's violin concertos for orchestra - you realise that sound, as such, wasn't paramount for him. What counted was the musical thinking."

And though Perahia has a large harpsichord beside the Steinway in his studio, he has no interest in playing Bach on it. "I use it to investigate the effects which Bach himself could achieve, but then I transplant them onto the piano. I believe in the vernacular. People should hear music on the instruments of their time, as though it was written yesterday." He regards the amount of contrast you can get from the modern piano as vastly outweighing its "inauthenticity": "And with the Goldbergs, this means you can give every variation a different voice. It may not have been Bach's original intention, but it can only help the listener concentrate."

That other great Bachian, Andras Schiff, asserted recently that the sustaining pedal was the enemy of polyphony: the whole of Bach's oeuvre, he claimed, could be satisfactorily played without it. Perahia takes the opposite view: "If the pedalling is heavy it can muddy the counterpoint. But the particular beauty of the harpsichord is that it can melt one tone into another - and the only way you can get that effect on the piano is through the pedal. If you really want to be authentic, pedalling actually helps."

So what is Perahia's view on the drily détaché Bach - every note picked out semi-staccato - as purveyed by the late, great Glenn Gould and his mentor Rosalyn Tureck? Perahia refuses to name names, but dismisses their style as absolutely contrary to Bach's intention. Every keyboard piece Bach wrote, he says, has a chorale as its framework: a coming-together of the individual voices which make up the counterpoint. "And don't forget, Bach himself was known as a great legato player."

Perahia's late-flowering passion for Bach was triggered by a strange and disturbing experience. "One day, my thumb blew up with an infection. I took antibiotics for a few days, then it got better and I could play again." He was so sure things were sorted that he didn't bother to finish the course of treatment, but two weeks later the thumb blew up again. "And nothing could get it down. I asked the doctor to put me back on the antibiotics, but he wouldn't, because by that time he knew it was something else. For a while they thought it was a ligament, but in the end it was diagnosed as a spur on the bone, which seriously inhibited movement."

He was duly operated on and, after a year away from the keyboard, went back to playing, but the trouble recurred. "And I was off for another year, and this time I felt very low: I thought I'd never play again." How did he pass the time? "I read a lot - theorists on music like Heinrich Schenker. And I played chess against a machine, and always lost. I spent the year getting depressed. It was a terrible time. Apart from my wife and sons, what really got me through was listening to Bach."

If the operation hadn't worked, he would undoubtedly have gravitated to the podium: he's spent a lot of his adult life as a conductor, and conducting was what he chose to study - alongside composition - when he entered Mannes College as a 17-year-old in New York. "I loved the piano, though I didn't practice seriously until I was 15. All I knew at that time was that I wanted to do music, and composition always interested me - it still does. I gave it up, because I couldn't find the language.'

How come? "I'm stuck in tonality. I can't leave it, to find my own language." He had wanted to follow the trail blazed by Bartok and Hindemith, and push things on a bit further; he'd written piano pieces, and a work for voices based on a psalm, but to no avail; he didn't even bother to keep copies of these compositions.

So here's an odd situation: Sony's 25th anniversary set of Perahia's recordings includes his superb performances of sonatas by Tippett and Berg, yet he protests that he doesn't understand their language. And he doesn't respond to Boulez? "No." Or Schoenberg? "No. Though I think he was a great musician. I just don't understand 12-tone music. I'm very ashamed of it, but there it is." His manner of saying this suggests no shame at all - indeed, rather the reverse, as he reinforces his point. "Nature has a very strong way of punishing people who go against tonality, and I think Schoenberg was punished. Dissonance is by its nature painful, and has to be resolved. This has become a great truth for me - though I started out as an ardent modernist."

So has music - the real stuff - run its course? "Not necessarily. There's still time for a genius to emerge." But isn't this sad? "Well, music as we know it took a long time to happen. With certain exceptions, I feel the same about music before Vivaldi and Bach as I do about contemporary music. There are outstanding talents today - Harrison Birtwistle for example - though I don't respond to them, not remotely. In order to understand their language we need quite different guidelines from the ones we use for Bach and Beethoven. With those composers even rhythm was governed by tonality. If tonality goes, the whole basis of music is gone. If a genius were to acknowledge this problem, they could perhaps do something, but nothing can start till it's acknowledged."

He doesn't think "world music" offers any route forward, even though his hero Bartok made use of it. "Because music is very much man-made. It gets hints from nature, and from the folk idiom, but the construction of late Beethoven or Schubert or Bach has nothing to do with that. Their linear progessions, their harmonies, are so complicated and so refined - they're on a much higher level of thought than folk music. What interests me is music which can show the accomplishments of the human mind."

His next recording will be of Chopin's Etudes, but what really engrosses him now is Bach's Art of Fugue. "A fugue is a poem, an expression of a spiritual state, not a mathematical exercise, and that work is beyond me. All I can say is that, as time goes by, I'm getting a bit closer."

And the thumb? "Great, it doesn't bend but it gives me no pain. I don't even think about it." The recordings certainly corroborate that.