The incomplete works of Mozart and others

A British opera company has upset classical purists by appending their own ending to Mozart's opera Zaide. A look at other great unfinished pieces of work.

For some, adding to Wolfgang Amadeus Mozart's work would be like drawing a moustache on the Mona Lisa. This, however, is what Britain's Classical Opera Company have just attempted - they are currently touring Britain with a new version of Mozart's unfinished early opera Zaide, with a new ending tacked boldly on the end. Mozart only completed two acts of the opera (at the age of 24), though one show-stopping aria - Ruhe Sanft - has made it into the repertoire, so the company have cobbled together a final act, with new English dialogue, from other Mozart pieces of the same period.

Unsurprisingly, this brave step has raised some people's hackles, and reviews of the finished piece have so far been patchy. The question the production raises, however, is a very valid one: what do you do with a brilliant score that is close to completion but not quite ready for performance? Leaving it to moulder forgotten in some archive seems a terrible pity when the muscles and sinews of the finished piece are all but there already. Written at a time when life was often cut short even before middle age, many fine pieces of classical music were left unfinished by their composers. In tribute to the spirit that has brought Zaide to the stage, here is a round-up of some of the great, unfinished works that nearly never made it to light, works whose absence would be a terrible loss to audiences.

Who really wrote this incredible piece of music? Commissioned in the 1790s by an Austrian count who hoped - ludicrously - to pass the piece off as his own, the origins of this great Mass were long covered in a blanket of secrecy. A product of obscure, mixed authorship, it was even rumoured that Salieri, Mozart's rival, had commissioned the Mass, a myth explored by Peter Shaffer's play Amadeus, which was later made into a film. This secrecy, it turns out, was created almost entirely by Mozart's widow Constanze, for that most human of reasons: money.

The Mass had been commissioned by an aristocratic musical dilettante named Count Von Walsegg, but when Mozart died before its completion, his widow was desperate to make sure she got the final outstanding payment. Enlisting the composers Joseph Von Eybler and Franz Suessmayer to complete the work (according to instructions that she insisted her husband laid down shortly before his death), she then passed it off to the Count as Mozart's work alone. Ultimately, the other composers' role in finishing the piece came out, but it was still in Constanze Mozart's interest to downplay this in order to make sure her share of royalties was secure. No one ever came completely clean about who wrote what. For some reason, this doesn't seem to matter: the final piece is of such towering, ground-shaking brilliance that it has gained almost total acceptance as a definitive version. Composed on the cusp of the romantic era, its brilliant use of counterpoint (rather than melody) actually looks back to the Baroque era, creating powerful, resonant music that is a world away from the easy charm and invention of Mozart's lighter music.

While he had arguably the greatest song-writing talent in classical music, Franz Schubert was pretty rubbish when it came to finishing symphonies. The 8th was the composer's second orchestral suite never to be completed (his 7th symphony is even more fragmentary), and with six years until his death at the age of 31, he had plenty of time to finish it if he had cared to. What remains, however, is still one of Schubert's most popular works after his songs, an effortlessly tuneful but powerful piece full of the sort of restrained but unmistakable emotional pull that makes the composer's music so affecting. Exactly why it is unfinished remains a mystery - as do many other things about the piece. Do the torn pages in the manuscript possibly suggest that Schubert's friend Anselm Huettenbrenner destroyed the two remaining movements? And why did Huettenbrenner wait until 37 years after Schubert's death to reveal the two movements the composer had completed? Whatever the answer, it remains a sad reminder of a time when high early mortality rates meant that major artists couldn't, like us, depend on finding time for unfinished projects in their later years.

Gustav Mahler's final symphony pays witness to a life in freefall. Devastated to discover that his wife Alma was having an affair with the architect Walter Gropius, Mahler resorted to analysis with Freud while writing the symphony in 1910. This apparently helped him somewhat, but the resulting music remains anxious and sometimes even tortured. The composer's score underlined this, scrawled as it was with despairing notes to his wife - he even wrote "To live for you! To die for you" on the final page of the last movement. Die Mahler did, unfortunately, aged 52, of a throat infection later that year - leaving this piece tantalisingly close to completion but still unperformable. What he left, however, was of extraordinary quality, at turns eerie and passionate, with doomy and joyful melodies jostling each other in an extremely intense, varied whole. The job of piecing this beautiful, fragmented piece together unfolded over decades. First the two movements that were essentially complete were fair copied and performed in the 1920s (though still rejected by some figures). Then in 1960 the remaining three movements - which had their themes and variations all written but had not been orchestrated - were completed by the British musicologist Deryck Cooke, and warily given the green light by Mahler's widow, Alma. While some insist that Cooke misrepresents Mahler's intentions (a statement few of us are in a position to contest), his adaptation is still unmissable, a musical roller-coaster ride that shakes the audience but ultimately ends in blissful serenity.

It's hard to believe that one of history's most performed operas wasn't even finished by its composer. When Giacomo Puccini died of throat cancer in 1924, he left 36 sheets of sketches to help a future composer complete Turandot's half-written final act. Exactly how this final act should end - or whether ending the work at all is a travesty - has remained a bone of contention ever since. The shaky consensus is that the 1920s version put together by Franco Alfano is the closest to Puccini's intentions, though new versions have been written and performed right up to the current decade. Given the massive popularity of the music - the epic, soaring Nessun Dorma is arguably the best known opera aria ever -the opera's plot and its strange sadism come as a bit of a surprise. It presents the audience with the icy Chinese princess Turandot, who has all her suitors executed if they fail to answer three riddles. So intensely expressed is her loathing for men that her ultimate love for Calaf, the one suitor who answers the riddles, seems abrupt and unconvincing. Could it be that Puccini failed to finish the opera because he couldn't see a way out of this inconsistency? The abruptness of this change of heart, and the music's slightly mixed authorship, means that Turandot as a whole has never been quite as popular as the lush, faintly Chinese influenced arias that have made it famous.