What ‘the most important Mozart discovery in decades’ sounds like

In 1778, a young musician named Marie-Louise-Philippine de Bonnières de Guînes was sitting in a composition lesson in Paris, trying to come up with a melody. She racked her brain for 15 minutes. Finally, her teacher — Wolfgang Amadeus Mozart — wrote the beginning of a tune and asked her to continue it.

“Look what an ass I am,” he told her, as he recounted in a letter to his father. “I started a minuet, and I can’t even complete the first part — would you be kind enough to finish it?”

In the letter, Mozart complained that his pupil, a duke’s daughter who was a talented harpist, completed her music theory exercises well enough, but “had no ideas at all”.

That may have been exasperating for Mozart, but it has given posterity a spectacular gift. Late last week, the National Library of France announced the discovery of a 44-page notebook from de Guînes’ lessons. The notebook offers an extraordinary window into Mozart’s teaching method, showing his corrections and improvements on de Guînes’ work.

The discovery also yields repertoire pieces marked by Mozart’s imagination: seven previously unknown works for flute and harp. Experts say that while de Guînes composed these works under her teacher’s guidance, Mozart penned a substantial portion of the music himself.

“This is the most important Mozart discovery in decades,” Armin Brinzing, the director of the Mozart Library at the International Mozarteum Foundation in Salzburg, Austria, said in a phone interview.

The newly discovered works were played publicly for the first time on Sunday at the National Library of France, performed by flutist Mathilde Caldérini and harpist Nicolas Tulliez, both members of the Orchestre Philharmonique de Radio France. Their recordings of the pieces will be broadcast on France Musique radio on Monday.

François-Pierre Goy, a conservator at the National Library, said he had been looking through a stack of anonymous manuscripts in February, hoping to fill in details about them before he retired, when a notebook caught his eye.

It showed the kind of harmony exercises that he had been required to practice as a student. There were two distinct styles of handwriting — a pupil’s and a teacher’s — and the teacher had an unusual way of drawing certain musical signs.

Goy looked more closely at the teacher’s handwriting. He examined notebooks from lessons that the composer had given later in Vienna and an autographed copy of a Mozart score in the library’s collection. The similarities were striking.

“I couldn’t believe my eyes,” Goy said. He was wary of being let down, so he consulted musicologist Laurence Decobert, who was also convinced that they were looking at Mozart’s hand. In April, Brinzing travelled to Paris to authenticate the manuscript.

“It is very clear,” Brinzing said, “that it is Mozart’s handwriting.”

Thanks to Mozart’s letters, scholars knew that he taught de Guînes from May to July 1778. The manuscript allows them to study his exact teaching method.

“You can follow basically bar by bar,” Brinzing said. “What did she write? What did Mozart correct?”

“It’s fascinating,” he added, “to compare that.”

The Duke of Guînes hoped that his daughter would become a competent enough composer to write sonatas for flute and harp, the instruments they played. Most of the rediscovered pieces are light, short works, and one is incomplete. But Mozart corrected another of them, a fast movement lasting about five minutes, to such an extent that “roughly three-quarters to 80 per cent should be by Mozart,” Goy said.

Tulliez, the harpist, said that piece was a major addition to the repertoire. Before Friday, the only Mozart piece with his instrument was the Concerto for Flute, Harp and Orchestra in C major, K. 299, which Mozart wrote in the same period for the Duke of Guînes and his daughter.

The rediscovered fast movement “is going to definitely become one of our main works”, Tulliez said.

Both Tulliez and Caldérini, the flautist, said it was the strongest work in the set. Still, when they began rehearsing the pieces, the sheet music that Goy had prepared using the notebooks didn’t differentiate between teacher and pupil. Without seeing the handwriting, it could be hard to untangle Mozart’s musical voice from de Guînes’.

“It was not so easy, to guess who wrote what,” Caldérini said.

She also wondered whether Mozart was being overly harsh with his student. “He was very demanding, because he was so talented and so young,” she said. “Maybe he couldn’t understand that it was not so easy for someone else to compose.”

Now, the dynamic that frustrated Mozart is precisely what makes the manuscript so valuable. A more inspired pupil would have given him less to do. Despite his laments, their lessons produced music of extraordinary grace.

The music, Goy said, is “worthy of living.”

This article originally appeared in The New York Times.

Start the day with a summary of the day’s most important and interesting stories, analysis and insights. Sign up for our Morning Edition newsletter.