Mozart and his wife Constanze spent the months of August through November
1783 in
Like the Requiem (K. 626), the "Great" C minor mass survives only in incomplete form. In the case of the Requiem, Mozart died while working on the piece, but the story surrounding the C minor mass is much less clear. The last movement for which materials survive is the Benedictus, but a liturgically complete mass would require additional sections in the Credo and an Agnus Dei at the end. Scholars are uncertain as to whether Mozart did complete a new mass (in which case some movements have been lost), or whether, short of time in advance of the first performance, he was forced to re-use movements from works he had already completed. (It is taken for granted that the first performance, as part of a Roman Catholic service, necessarily accounted for all sections of a proper mass one way or another. Regrettably, a detailed account of this performance has not been discovered, and information about any later performances is also too vague to be helpful.) An edition prepared by Alois Schmitt in 1901 "completes" the mass, as Mozart himself may have done, by substituting movements from other pieces. Most performances today, however, limit themselves to the movements Mozart wrote specifically for this piece. Even then, some input from editors is necessary. For many movements, no manuscript of the score has been found, so it must be reconstructed from the surviving parts; in additional cases, even the set of parts is incomplete, requiring that missing melodic lines be recreated by extrapolating from the overall texture.
Leaving aside these uncertainties, the "Great" C minor mass is unmistakably by Mozart. Moreover, it represents a tremendous step forward in his choral writing. The solo voices are provided with unusually lengthy melismas and other vocalizations on single vowels, representing a shift in the composer's focus from text setting to "pure" vocal effects. The most striking example of this is the cadenza in the Et incarnatus est, in which the soprano and three solo woodwinds form a musically balanced quartet of interweaving melodic lines, all while the soprano sings the "a" of "factus est." The increased attention on vocal ornamentation for its own sake probably stems from Mozart's intensifying interest in opera during this time. Idomeneo and The Abduction from the Seraglio had been completed and premiered within the last two years; Abduction was Mozart's most successful stage work to date, and it cemented his popular reputation as one of the great composers of the day.
Equally striking with respect to Mozart's overall development as a composer are the severe differences in character and style between movements. The Laudamus te and the Domine are effortlessly elegant in their simplicity, with the texture generally made up of one or two melodic lines and a simple accompaniment, while the two Osannas feature the choir divided into eight parts, giving rise to a fantastically complicated interweaving of equally important voices. Another contrasting element is the degree of chromaticism in each movement. Much of the piece is essentially diatonic, with dissonances that would not have seemed unusual to an eighteenth-century listener. Newly aware of dramatic possibilities even in the context of sacred music, however, Mozart elected to emphasize certain sections of the mass text with a much weightier treatment; among these more harmonically inflected movements, the Qui tollis stands out. The orchestra is locked into the unyielding motion of a solemn processional, with remote harmonies and unexpected suspensions that reinforce the gravity of the text, "Qui tollis peccata mundi" ("You who take away the sins of the world"). Later in the same movement, on "miserere nobis" ("have mercy on us"), the orchestra drops down to minimal volume, while the two sections of sopranos take turns on an eerie, chromatically descending line.
Sacred choral music was important to Mozart throughout much of his career, but he would not attempt another mass until turning to the Requiem in the final months of his life. In the "Great" C minor, Mozart's mature gifts as a vocal composer, and his flair for the theatrical even in a formally rigid setting, are in full display. From a liturgical standpoint, the mass may be missing some sections–but as a piece of music, it feels entirely complete.