Composing Imitative Counterpoint around a Cantus Firmus: Two Motets by Heinrich Isaac

In the decades around 1500 composers learned to combine the new style of imitative polyphony with the older practice of basing a work on a cantus firmus. By applying Peter Schubert’s technique of modular analysis and his descriptions of common contrapuntal techniques to Heinrich Isaac9s Inviolata integra et casta es Maria and Alma redemptoris mater, we can learn a great deal about compositional process in the period. Inviolata, which features a cantus firmus in strict canon after two measures, consists of two-, three-, and four-voice modules. Moreover, understanding the modular construction of the piece makes it possible to reconstruct the missing contratenor 2 part. In Alma redemptoris mater, which features a tenor cantus firmus that uses both long-note presentation and free paraphrase, Isaac uses four-voice modules, imitative presentation types involving modules, and nonmodular contrapuntal techniques probably derived from improvisatory practices. Understanding and labeling the contrapuntal techniques used in composition of this period allow us to analyze the music with a new precision, and to describe the differences between composers and genres.