Week 4: Cantus FirmusLike canons and inventions, chorale preludes are polyphonic elaborations of preexisting material called the cantus firmus. The cantus firmus is a formal object, typically AAB, that lends its form to derivative works which employ contrapuntal means to fragment, mirror, echo, and re texture the cantus firmus in other voices. While they can be subsumed under the techniques of chorale prelude, depending upon instrumentation and the manner in which they are elaborated, these derivative works are also called: chorale motet, chorale fantasia, chorale variations, chorale partita, chorale fugue, or chorale cantata.
The poplar's trunk (detail to right) unites the ground to leafy canopy and sky above. The tree is analogous to a preexisting melody stitching the elements of a composition together. In music, we call this melody a cantus firmus. Because Bach used the chorale, his cantus firmus works for organ are called chorale preludes. But, as a procedure, the techniques of chorale prelude apply to any polyphonic elaboration of a preexisting melody.
The cantus firmus has its own form--some melodies are binary (AB) while others are ternary (ABA). Monet's detail to the right might be considered a binary, with sky at the top being part "A" and leaves at the bottom being part "B." The Lutheran chorale typically subscribes to an extended binary in which section "A" (called the Stollen) is repeated and followed by a section "B" (the Abgesang) which is not repeated. This AAB schematic is known as German bar form.
Chorale preludes state the cantus firmus in one or more voices with remaining voices providing suitable counterpoint. Naturally, the resulting prelude replicates the form of the cantus firmus upon which its elaborations hang. So, if its cantus firmus subscribes to bar form, then the chorale prelude, too, will be in bar form. The cantus firmus is the glue, then, that lends form to the prelude and keeps its parts from falling apart. The following links will introduce you to various ways the cantus firmus can appear. As you study them, keep an inventory of which chorales (and their preludes) are in bar form and which are not.
Musical examples in this unit can be played from the Cantus Firmus disk. Please check this disk out and insert it into the ROM drive at this time. Next...
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