The new treatment of traditional plainchant, as in the technique of paraphrase, shows Renaissance composers taking a relaxed attitude toward medieval authority. The same can be said of their reaction to medieval intricacy, as represented by intellectual musical devices such as isorhythm. Fourteenth-century composers like Machaut (page 55) had used isorhythm even when writing love songs. Composers now cultivated a much simpler style for their polyphonic songs, or chansons: simpler, gentler, and more supple. The modest style of these new chansons was sometimes used for sacred texts, including portions of the Mass.

The rejection of isorhythm did not mean, however, that composers abandoned the technical development of their craft, which had taken such impressive strides from the early days of organum. Rather, such efforts now were focused on large-scale musical construction. For the first time, compositions were written to last — and to make sense — over twenty or thirty minutes.

The problem of large-scale construction that fascinated fifteenth-century composers was how to write music that would hold together throughout the Mass, the largest and most important prayer service of the Christian liturgy. The Mass contains numerous items that were sung in plainchant, and as we have seen, for centuries — from the time of organum to the time of harmonized hymns — composers had been embellishing plainchants with polyphony to be sung in services. The next step was to set the words that had been chanted to new music, instead of embellishing the existing chant music. Composers settled on these five items of the Mass for their new music:

In this way the polyphonic Mass was standardized into a five-section form, and it has retained this form down to the present day, in settings by Palestrina, Bach, Mozart, Liszt, Stravinsky, and many others.

One of the earliest ways to unify these disparate elements was simply to use the same music to open each movement. Another way was to base each movement on the same Gregorian chant — one belonging not to the Mass, but perhaps to the liturgy of some special day on which the Mass was celebrated. This would make the Mass especially appropriate for Christmas or Easter or (as we will see shortly) Corpus Christi, a celebration held every year in springtime.

So large a structure presented composers with a challenge, and they took this up in a spirit of inventiveness and ambition characteristic of the Renaissance. What the symphony was to nineteenth-century composers and their audiences, the Mass was to their fifteenth-century counterparts: a brilliant, monumental test of artistic prowess.