Why Does a Passacaglia Keep Moving over a Repeating Bass?

A passacaglia commonly organises continuous variations over a recurring bass line or harmonic scheme. On the surface, this may appear to hold the music inside one cycle. Its real effect is almost the reverse: because the foundation remains recognisable, changes in texture, harmonic density, register and rhythmic activity become easier to hear. Repetition is not the opposite of development; it gives change a scale against which to register.

Bach's Passacaglia and Fugue in C minor, BWV 582 begins by presenting its eight-bar theme alone, then unfolds twenty variations. The bass does not simply remain in the lowest voice in an unchanged form. At times it plainly supports the lines above; elsewhere it is ornamented, displaced or allowed to recede from the foreground. The Los Angeles Philharmonic's note also describes how the work draws on the solo chaconne and eventually transforms its material into a double fugue. The theme is therefore not merely repeated: its function changes through successive reorganisations.

There is no need to count every variation while listening. First remember the theme's descent and return, then notice what happens at each new cycle: does the register widen, do the voices thicken, does the rhythm become more active, or does material first heard in the pedals move into the manuals? The sense of progress comes from these differences accumulating over a fixed framework.

Piano transcriptions can too easily turn the work into one long, monumental crescendo. It matters more to preserve the character of each textural layer. Lighter variations need transparency so that the dense passages can genuinely feel larger; the bass must retain direction without flattening the voices above. The power of a passacaglia lies not in an unchanging bass alone, but in making every change impossible to miss.

https://imslp.org/wiki/Passacaglia_in_C_minor%2C_BWV_582_(Bach%2C_Johann_Sebastian)

https://www.laphil.com/works/passacaglia-and-fugue-in-c-minor-bwv-582-bach-arr-labadie