← Bach · Well-Tempered Clavier
Prelude 21 in B-flat major BWV 866
Book I of the Well-Tempered Clavier. Under its figuration, this prelude is 33 chord changes across 20 bars — ranked 28 of 42 by measured difficulty (advanced) in this survey. Played as block chords, it's a progression you can learn in an afternoon; the piece is that progression wearing sixteenth notes.
Practice this piece → Practice chords → Learn it section by section → Hear the harmony →
How it opens
The first changes are vi7 (D) · IV7 (Bb) · iii7 (F) · vi7 · vii7 · I7 (F) · vi7 · V7 — and the whole prelude keeps moving at roughly that harmonic pace.
What it leans on
Of 33 labeled changes, the harmonies that do the most work: V7 (5×), iii7 (F) (4×), IV7 (Bb) (2×), vi7 (2×), V7/IV (2×).
Free scores
- Blocked-chord reduction (MusicXML) — the harmony skeleton the player performs
- The prelude as written (MusicXML)