Fugues, canons, rounds -- what is it about shifting, imitative counterpoint that propels musical expressions forward with such compelling conviction? The mind's ear receives continual audio patterns that make sense only in retrospect. Yet it is the expectation of future events that these reflections are set against. Harmonic motion also depends on the listener's ability to remember past events to establish the tension and subsequent resolution of vertical sonorities captured in the present.

The juxtaposition of harmony and counterpoint into a contrapuntal form finds its greatest examples in the temporal architectures of Ockeghem and Bach.

In the fifteenth century, the superlative technical feat of Ockeghem's mensural canon that underlies his Missa Prolationum does not detract from the work; rather, the complex independent interweaving of linear movement throughout the voices supports a depth of spiritual power that has rarely been matched since his death in 1497.