Why Does a Musical Sequence Move While Repeating?

A sequence does not state a passage again at exactly the same pitch. It moves a recognisable melodic or harmonic model to a new pitch level. We hear that the relationships have been retained, yet we also hear the point of arrival shifting. Repetition therefore creates direction instead of standing still.

The repeating bass of Pachelbel’s Canon in D is often remembered on its own, but another kind of motion unfolds above it. Once a short figure enters, it can continue at new pitch levels while its note values gradually become more active. The familiar contour lets the ear follow; the change of position lets the music accumulate. Strictly speaking, sequence, ground bass and canon are not the same concept. They may occur together, but they answer different questions: how material is transposed, how the bass cycles, and how voices imitate one another in succession.

At the piano, a sequence can easily become several equally weighted copies. A more musical approach is to hear where the model begins, where each copy moves, and whether the harmony is increasing tension or approaching a cadence. The touch may preserve a common shape, but dynamics and phrasing should serve the direction of the whole passage. A sequence enlarges musical space with limited material, making change sound both new and clearly derived from what came before.

https://viva.pressbooks.pub/openmusictheory/chapter/diatonic-sequences/

https://imslp.org/wiki/Canon_and_Gigue_in_D_major%2C_P.37_%28Pachelbel%2C_Johann%29