ozart's two greatest religious works were left unfinished, but for very different reasons. The Requiem, as everyone who has seen or read one of the versions of Amadeus knows, was interrupted by Mozart's own mortal illness. The Mass in C Minor, K. 427, Mozart's other monumental sacred work, remained in an incomplete state for reasons that are not clear.

Between the ages of sixteen and twenty-four, Mozart was in the service of the Archbishop of Salzburg. Uncongenial restrictions as to the duration and dimension of music in the liturgy and severe limitations on his ability to travel to the other musical centers of Europe to advance his secular musical career created a climate of frustration for the young composer. Even so, the dozen or more masses, the Litanies, Vespers, short sacred works and church sonatas that he wrote during this period constitute a set of impressive credentials for the young genius.

After separation from the Archbishop's service Mozart never again returned to sacred music except for the late motet Ave verum corpu and the two works noted above. The tragedy of their incompleteness is therefore all the more poignant because of the surpassing beauty of the parts of those masterpieces that do exist.

Mozart was smitten in turn by the charms of three sisters of the Weber family, all of whom must have been extraordinarily gifted singers. The eldest, Josepha, was the first Queen of the Night. The second, Aloysia, kindled his fires from the time she was fifteen. But it was Constanze (largely through the machinations of Mama Weber) who became his bride in 1782.

And it was for her that the exquisite Et incarnatus est of the Mass in C Minor was written. Whether the Mass as a whole was composed as a wedding gift for Constanze or in honor of a vow of thanksgiving for her recovery from illness is not clear. It is known that the Mass was performed in some fashion at St. Peter's Church in Salzburg on October 26, 1783, near the end of the visit Mozart made to his family for the purpose of introducing them to his new wife.

But why does the Mass stand in a half unfinished state? One possibility is that, wedding promise aside, Mozart treated the composition as a learning exercise in new technique — his acquaintance with the works of Handel and Bach was expanding rapidly — and completeness was therefore not a compelling issue. Another, purely practical possibility is that since the Mass was not a commissioned work, the pressure to complete other works for which payment was promised took precedence. In any event, what we have is a complete Kyrie and Gloria, a Credo of only two movements (fragments really of what surely would have been a grand sequence of pieces), a Sanctus missing one of its two choruses, a Benedictus missing its second chorus in the da capo, and no Agnus Dei at all.

It is likely that the Salzburg premiere was filled out with plainsong settings, and that is a solution same recent performances have made. Some older editions solved the problem of completeness by inserting textually appropriate movements from other Mozart masses. This solution, however, seems to do violence to aesthetic continuity, as all of his earlier mass settings seem to derive from a different expressive world from that of the C Minor Mass. This cafeteria concept of picking and choosing more at less at random from among his other settings is really no solution at all.

In this performance we will perform only the movements Mozart completed or which were completed by others from materials adequate to the task. Mostly, we have relied on the work of the English musicologist Richard Maunder for decisions relating to orchestration. Since this is a concert and not a religious setting, we have not felt the need for completeness in the liturgical texts.

The Boston Cecilia performed this work at New England Conservatory's Jordan Hall in Boston on April 13, 1997.