In his 2008 article, David Temperley introduced the concept of hypermetrical transitions -- gradual shifts from even-strong to odd-strong hypermeter, or vice versa), shifts that involve conflicting metrical cues. While he provides convincing examples of this idea, he does not offer one example of hypermetrical transitions -- those that occur in imitations, where two conflicting hypermetrical strands are represented by distinct textural parts. The present paper attempts to fill this gap by exploring hypermetrical transitions in canons in Mozart's chamber music.
My central claim is that individual parts of a two-voice canon not only produce a metrical conflict due to their melodic identity, but also allow for different -- and conflicting -- interpretations of harmony at the middleground level. According to William Rothstein's (1995) "rule of harmonic rhythm," each hyperdownbeat, hypermetrically strong downbeat) signals a change of harmony. In an imitative situation, each voice suggests its own pattern of harmonic change at a middleground level. Each pattern can then be mapped onto its own distinct prolongational reading of the passage, expressed in the form of alternative, and conflicting) Schenkerian graphs, rendering the hypermetrical transition as a kind of "prolongational transition." The smoothness of a hypermetrical shift is then measured by the extent to which the two readings are equally well-formed. If both voice-leading interpretations are equally viable, the transition is smooth. If, however, one reading is in some way inferior, the transition is more sudden, since the harmony projects one hypermetrical pattern stronger that the other.