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Composed: 1782

Orchestration: flute, 2 oboes, 2 bassoons, 2 horns, 2 trumpets, 3 trombones, timpani, organ, strings, 2 sopranos, tenor, bass, and chorus

First Los Angeles Philharmonic performance: May 30, 1971, Gerhard Samuel conducting

About this Piece

“I made the promise and hope to be able to keep it,” Wolfgang Mozart wrote to his father on January 4, 1783. “The score of half a mass which is still lying here, waiting to be finished, is the best proof that I really made the promise...” The “promise” was to write a major work for Salzburg, the “half a mass,” then, being the present gigantic torso.

The letter contains the only reference Mozart himself ever made to K. 427, which was probably begun in July of 1782 and sporadically worked on in the summer of 1783.  

The Mass was performed in its “entirety”—which is to say that Mozart must have borrowed from other works to make it complete and suitable for liturgical performance—on October 23, 1783, in the composer’s presence—he may have presided at the organ. The venue was St. Peter’s Church in Salzburg; it is likely that Constanze sang the high-lying first soprano part.

The Mass in C minor works, even if not as a work for the sacred service, as the composer left it. Why he left it, however, remains a matter of conjecture.

But there is yet another seeming mystery regarding the Mass in C minor, only partially explained by the letter quoted above and the conclusions to be drawn from it: Why he wrote the Mass in the first place; why, freed from the tyranny of his employment at the Salzburg court and relocated to Vienna, where church music was not in demand (at least not of him), should Mozart have set himself such a task? 

The most logical explanation—supported to a considerable extent by the score itself—is the great discovery that Mozart made just before he started on this work: the music of the late-Baroque, most importantly that of Johann Sebastian Bach and Handel, which had until then been generally regarded as hopelessly dated.

To sum up, what Mozart did write for the C-minor Mass was the Kyrie, Gloria, Credo (through “Et incarnatus est”), Sanctus, and Benedictus. For “Et incarnatus est,” Mozart notated the vocal lines, the obbligatos for flute, oboe, and bassoon, and the bass, with the string parts having to be filled in by later editors. The “Osanna” lacks the customary second chorus, so that has had to be completed via clues provided by the orchestra parts.

The reconstruction of this tremendous creation did not begin until early in the 20th century, instigated by the efforts of the German musicologist Alois Schmitt. The music of the Credo, Sanctus, and Hosanna heard in these performances was reconstructed and completed by Helmut Eder. Herbert Glass