THE highly imaginative music of Robert Schumann has long intrigued, perplexed and haunted music-lovers.

Everyone acknowledges its troubling beauty but even those who (like me) adore it recognise it can often be enigmatic, obsessive, even chaotic. These qualities don't deter its fans . . . indeed, they are part of its allure . . . but it is tempting to wonder about the balance of Schumann's mind.

Schumann was a literary man as well as a musical genius and, in addition to being an eminent music journalist and editor, he wrote extensive diaries and letters. Biographers have long struggled to make sense of the highs and lows he recorded so perceptively. His final illness, and his death at 46 in a mental asylum in 1856, were described by others, including his doctors.

All this has led historians to believe his final breakdown was the furthest outpost on a long journey into mental illness. They have seen him variously as manic depressive, as a suppressed homosexual, as suicidal and schizophrenic. His mood swings and thoughts of death are read as the first steps on the road which ended with him in a straitjacket, shouting and deluded, his wife Clara forbidden to see him in case he harmed her.

John Worthen sets out to persuade us Schumann was never mentally ill. First, he thinks Schumann's ups and downs were always within the bounds of sanity.

Secondly, he believes the evidence points to Schumann's final illness as being not mental breakdown but the tertiary stage of syphilis.

An early episode of the disease has often been mentioned but Worthen asserts that syphilis caused Schumann's final illness . . .and much of the "unbalanced" behaviour which preceded it.

There's an excellent account of the day Schumann tried to drown himself in the Rhine and his deteriorating health is tracked in minute and distressing detail.

In an age when we have more understanding of mental illness, it's almost ironic that a new biography should pop up with the theory that Schumann wasn't mentally ill at all. Worthen draws on modern medical research to prove his case. When Schumann "went mad" in 1853, his doctors were not in a position to link his symptoms with his syphilitic infection of 1831. Schumann thought he had been cured at that time and his belief seemed to be borne out by the fact neither his wife nor his children developed the disease. So when he experienced sensory and auditory hallucinations in the early 1850s, nobody would have suspected a long-dormant syphilis; it must have seemed all too likely that his wild imagination had finally tipped him over the edge.

We have always lacked good biographies of Schumann and this one will become a standard reference work. The late John Daverio's fine 1997 biography is more deeply attuned to the music but Worthen's is by far the most comprehensive account I have read of the facts of Schumann's life. His central thesis is important and he writes clearly and freshly, bringing a wise head to an intricate tangle of evidence. I have never read such a gripping account of the case Robert and his pianist wife Clara fought with her father, who opposed their marriage and tried to blacken Robert's reputation in a malicious feud.

Nor have I ever seen such a meticulous portrait of the Schumanns' married life. We learn about their "peculiarly modern relationship": how they divided the day at home so each could work despite the "thin walls", how they earned their income, how their seven children were looked after and how they organised Clara's concerts.

Musical life was as tricky then as now. Clara found there was precious little profit from tours once she had paid the expenses.

Robert's compositions were sometimes sold for less than Clara's income from a single concert. Throughout their 14 years together, they battled with money worries.

I would have liked to know even more, especially about Schumann's relationship with literature. He was a great reader, and there are many links between the books he loved and the music he wrote. He said that he had "learned more about counterpoint from the novelist Jean Paul [Richter] than from anyone", yet there are few references to Jean Paul and no analysis of his influence on Schumann.

The Romantic writer ETA Hoffmann, one of whose novels inspired Schumann's 'Kreisleriana', is not mentioned.

There's no exploration of the origin of imaginary characters such as Florestan and Eusebius, whom Schumann used in his diaries as voices of his "inner selves". Last, there are no substantial quotes from Schumann's critical writings. This is a pity because they show an incisive mind and lucidity not always evident in his music. Given that Worthen is a professor of literature, it would have been satisfying to hear his views.

There is one other omission . . .

the music. "I leave analysis of his music to those qualified to undertake it. This is a book about the lives Schumann led, not about the music he wrote, " Worthen says in the preface. This may be scrupulous modesty by someone who does not consider himself musically expert but it means he is forced to draw detailed conclusions about Schumann on the basis of biographical facts alone. Speaking as a player, and as a lifelong fan, of Schumann, I've always felt his music tells us things which may run counter to the facts, or at a tangent to them.

Having the music under one's hands for months and months, pondering it in the small hours of the night, observing its trajectory in performance, one gradually learns things about Schumann which, as Flann O'Brien might say, "are not taught in the national schools".

Though it may well be true that syphilis caused Schumann's final collapse, I wonder about the idea that he was never mentally fragile.

His combination of inspiration and helpless self-revelation is what we fans love about him . . . and is it really possible that someone in cold command of his mental powers would have produced such music?