A cantus firmus in the fifteenth century commonly borrows the tune from an excerpt of Gregorian chant (such as "Ecce ancilla Domini"), or from a popular song in the vernacular (the perennial favorite being "L'Homme Armé"); a composer of a mass would then quote this tune in each movement, perhaps varying the rhythm or ornamenting it. A rarer option is the sogetto cavato—an abstract musical subject made up for the occasion. In the 1501 collection of masses by Josquin Desprez printed by Petrucci lies an outstanding example of this technique: the Missa La Sol Fa Re Mi.

The particular group of intervals underlying this mass gives it its name. La, sol, fa, re, and mi are the Medieval solmization syllables for the pitches A, G, F, D, E. One of Glareanus' quasi-historical vignettes (in 1547) suggests that Josquin arrived upon this sequence by imitating a certain king whose phrase for unwanted courtiers was always, "Lascia fare mi" ("Leave me alone.") Whether or not this is true, virtually every moment of the mass derives from this little five-note phrase, either beginning on the pitch A, or, in a different hexachord system, on E. It is heard at various speeds as a cantus firmus in the tenor (as in the Credo), as a migrant cantus firmus in other voices (Kyrie I and Christe), as a subject of imitation (Hosanna I), and even as the subject of canon and rhythmic transformation (Agnus Dei I and III; here also the pacing of the cantus firmus accelerates till the end of the movement, using the aural tag as a vehicle for the climax). In Josquin's earlier Missa "Faisant Regretz," he had attempted the task of centering an entire five-movement mass upon a single short phrase; he allowed himself the leeway, however, of transposition. In this mass, in over 200 repetitions of the little five-note phrase, only once (the end of the Christe) does it diverge from A and E, yielding a remarkable, almost Impressionistic, unity of harmonic color to the whole.

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