He then came upon a copy of the original Faust text, dating from 1587. He set the closing chapters, depicting Faust's grisly end, for the 1983 Vienna Festival. Only after this Faust Cantata was performed did Schnittke feel impelled to use the 1587 cautionary tale as the basis for a future opera.
In 1988, The History of Dr Johann Faustus was but a prayerful hope. Schnittke put his sketches aside; the music was being composed entirely in his head. He knew how the opera should be shaped, and knew exactly where the irrevocable point in Faust's decision-making would come. This would mark the only break in the opera - a break that must leave us numb with shock. He also conceived a new character, Mephistophila, an antiphonal feminine infernal spirit.
Earlier, an outpouring of major works had reached a mature crest. 1985 saw the completion of the Choir Concerto, String Trio and Viola Concerto; and he had composed much of his First Cello Concerto and Peer Gynt (for the Hamburg Ballet) when he suffered his first stroke. When he recovered enough to be able to resume work, his musical tentacles were venturing forth on a musical and poetic phenomenon he terms Klangschatten - extensions of shadow-like sound that "we do not perceive consciously but are listening in on unawares". The origins of this sound-world can be found in some of the composer's film scores, which number more than 60.
This "shadow-sound" is a crucial aspect of Schnittke's straining to hear a world beyond our knowing. The philosopher Kant intimated the possibility of this world, while insisting that it was not within our capability to prove its existence. Nevertheless, Schnittke's preoccupations oscillate precisely on the boundary peering into this domain.
Musically, shadow extensions serve as many-layered, inspired sound-worlds in every work I have mentioned so far. But in his opera Life with an Idiot, they have a diametrically opposite effect: here they hem in and smother the spirit.
How did this opera, to be heard now in different opera houses throughout this country, come about? In brief, Schnittke decided a year or so after hearing Victor Erofeyev read his novella to a private audience, that this could one day become material for an opera in the tradition of Shostakovich's The Nose. Erofeyev, accurately predicting Schnittke's plans, began reshaping his text into a libretto.
But it was Mstislav Rostropovich who worked behind the scenes to secure a staging at Netherlands Opera of the as yet unwritten opera. Now Rostropovich, the most gentle and lovable of men, is also a crushing genius who can cajole and charm creative geniuses to leave off what they are doing, to do his bidding. And so Schnittke simply had to put aside his beloved Faust opera.
Then, in July 1991, when he was part-way into Act 2 of Life with an Idiot, Schnittke suffered another stroke. When he resumed work, the physical difficulty in writing meant the instrumentation had to become sparser and more condensed. Despite this, the already powerful sound of a smallish orchestra of 37 was not diminished.
At the first performances in Amsterdam in 1992, Boris Pokrovsky's cunningly claustrophobic production took the audience into the madhouse. For me, Hieronymus Bosch had come alive in the late 20th century. Like Bosch, Schnittke can imagine, in all its terrifying detail, the reality of hell, avoiding any temptation to rationalise.
"I", the opera's main character, is a pseudo-philosopher, a self-deceiver. His wife is good at commenting "sensibly" after the event in music that makes the Queen of the Night appear prim. She clearly prefers reading Proust to feeling passion for her husband. The musical shadows distance husband and wife from each other, encircling their self-absorption.
In Kafkaesque style, "I", as a punishment for his "lacking compassion", is forced to take a monosyllabic, onomatopoeic idiot into his home. By choosing Vova (Lenin's pet-name, as it happens), "I" sets in motion a Titania-Bottom chain of asinine infatuations that, in this case, leads to seduction, abortion, buggery and decapitation. Vova serves as an inculpable conduit for the demonic.
In Life with an Idiot, Schnittke's principle of calling into play a host of different styles (his so-called "polystylism"), and thus establishing his own special voice, is for once too damnably clever (like the libretto) and thus musically strained. Yet in Amsterdam I was gripped by having to face within myself a multitude of crazy truths I would have preferred to resist. After the third performance, I fled from the opera house down the road to a church where I might find healing in a performance about to begin of Schnittke's sublime Choir Concerto. Schnittke himself has said he sees the work as "open-ended". Yet, for me, the question of whether there is a way out from this vicious circle must continue to nag.
Schnittke did eventually complete his setting of the 16th-century German text of Faust (it will receive its world premiere at the Hamburg State Opera on 22 June). But he also realised his dream of resuscitating what logically he knew to be absurd - the re-invention of a recognisable symphonic form, in his Sixth, Seventh and Eighth Symphonies, composed over a span of a mere 18 months. (He had already done this in a different, equally convincing way some years earlier, in his Peer Gynt, to my ears the first symphonically thought-through ballet score in music history, Stravinsky and Prokofiev notwithstanding.)
Linked with the newly austere, heart-breaking frugality of the Eighth Symphony (specifically its first movement) is the concluding section of Schnittke's third opera, Gesualdo, which he had all but completed before suffering another stroke last year from which he is slowly recovering. The opera is scheduled to receive its world premiere at the Vienna State Opera on 26 May. Richard Bletschacher's cloistered libretto probes the famous Italian madrigalist's state of mind before and after he has his wife and her lover murdered, and ends with his self-mortifying penance. The score shows Schnittke summoning the lean, intense lines of Italian opera at the time of its birth.
The style of Gesualdo, and the very different sound-world of The History of Dr Faustus, promise to disclose acutely dissimilar aspects of Schnittke's music from the very black comedy that British opera audiences can experience over the coming weeks.
n `Life with an Idiot': opens tomorrow at ENO, London Coliseum, WC2 (0171- 632 8300), then 7, 10 April; opens 11 May at Scottish Opera, Theatre Royal, Glasgow (041-332 9000), then 16, 20, 25 May and on tour to Edinburgh and Newcastle
n A live recording of the world premiere, conducted by Mstislav Rostropovich, is available on two CDs from Sony Classical