Prelude 18 in G-sharp minor BWV 863

Book I of the Well-Tempered Clavier. Under its figuration, this prelude is 33 chord changes across 29 bars — ranked 31 of 42 by measured difficulty (expert) 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.

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Opening bars of Prelude 18 in G-sharp minor, reduced to labeled block chords — The opening, reduced: one block chord per change, functional labels above.

How it opens

The first changes are iv7 (G#) · V7 (F##) · V7 (A#) · VI7 (B) · III7 (A#) · iv7 (E) · VI7 (B) · iv7 (B) — and the whole prelude keeps moving at roughly that harmonic pace.

What it leans on

Of 36 labeled changes, the harmonies that do the most work: iv7 (G#) (3×), VI7 (B) (3×), i7 (D#) (3×), V7 (A#) (2×), iv7 (E) (2×).

Free scores

Blocked-chord reduction (MusicXML) — the harmony skeleton the player performs
The prelude as written (MusicXML)