These two works are pillars of the Baroque period, both utilizing the Passacaglia—a musical form based on a continuous variation over a repeating bass line (ground bass or basso ostinato).
Written: Circa 1706–1713 (Bach’s early career in Arnstadt or Weimar).
Summary: Widely considered the greatest organ work ever written, this masterpiece shows Bach taking a simple 8-measure theme and building an architectural wonder of 20 variations, culminating in a massive double fugue.
The Theme: The theme is 8 measures long, written in $3/4$ time. Interestingly, Bach likely borrowed the first half of the theme from a short work by French composer André Raison.
The Variation Structure: * Variations 1–15: The theme stays primarily in the pedals (the bass).
Variations 16–20: The theme moves to the manuals (the hands/upper voices), becoming more hidden and rhythmically complex.
The Fugue: Immediately follows the variations without a break. It is a Double Fugue, meaning it uses two subjects: the first half of the original Passacaglia theme and a new, faster counter-subject.
Harmonic Density: Bach uses "suspensions" and "passing tones" to create a sense of relentless forward motion that builds tension until the final $C$ Major chord (a Picardy Third).
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