Though maintaining a long and stellar career as a church musician, Johannes Ockeghem left only thirteen settings of the Mass Ordinary. This has led to the assertion that composition was only part of his professional activity. And yet the theorist Tinctoris praised him as the best composer of his age -- a man who helped rediscover the art of music. His surviving Mass settings help to justify this assertion; each in its way presents a complete musical solution to a unique compositional challenge. The Missa Au travail suis, of which fully four copies survive (three in Vatican Library manuscripts with the similarly opaque Missa Mi-Mi) is just such a work; in some ways it is quite unique in the context of fifteenth-century music.
The established practice of using a borrowed cantus firmus to melodically unify a mass setting involved quotation, elaboration, and possibly manipulation of that melody at least once in each movement. The Kyrie of the Missa Au travail suis follows this practice faithfully; in expository fashion, it presents a nearly exact version of the Tenor (middle) voice of the chanson Au travail suis (likely by Barbignant, though it is also attributed to Ockeghem), neatly apportioned between the three sections of the movement. The imitation featured in the chanson's opening is incorporated into the Mass opening as well. But from the Gloria onward, this clear presentation is completely abandoned. Each movement does begin with a headmotive from the chanson, and in each the Tenor quotes some ten notes of the model's Tenor; but the remainder of each movement is freely composed, and bears no formal relationship to the model.
The essence of the musical development, instead, is Ockeghem's often bewildering shifts of texture. The Mass is scored for a unique group of voices -- a nearly-equal upper pair, and a pair of basses an octave lower in overlapping ranges. (Ockeghem, himself a fine bass singer, showed a predilection for the lower voices.) Unlike similarly scored Mass settings from the turn of the fifteenth century, though, the pairs are largely equal in function. A large proportion of the Missa Au travail suis transpires in duo textures, punctuated by sudden chordal declarations (such as "Jesu Christe," "Miserere," and "Osanna in excelsis") and scintillating tutti closing passages.