The prelude is exemplary because of its natural voice-leading, making it a model for creating preludes strictly out of sequences, suspensions, and simple modulations. It seems to be constructed out of just one musical idea because we don't see any contrasting musical material, as in BWV 554 or BWV 556, for example. Therefore, the form of this piece is a period.
It starts with the phrase in the Tonic key (E minor, measures 1-4) and has a commonly-seen Frygian tetrachord in the bass (E-D-C-B, measure 4). In measures 6-9, the musical material moves to the relative major key (G major) and creates a perfect authentic cadence in this key (measure 9).
The next important modulation happens in measure 14 (B minor, the Dominant key). In measures 15-21, we can see 3 instances of sequences - No. 1 - descending (constructed out of V6 - and it's resolution, i), No. 2 - descending (chains of seventh-chords), and No. 3 - ascending (V6-i).
Just before the final cadence at the second half of measure 23, we can see a very colorful F first inversion chord, which in relationship to the home key of E minor is a Neapolitan sixth chord (a major sixth chord built on the lowered 2nd scale degree).
Despite its short length (25 measures only), this prelude can give much trouble for organists with modest organ skills because of several reasons: complex 4-part (at times 5-part) writing, syncopations and suspensions, and active pedal part.
However, slow tempo makes it accessible to organists with basic organ playing abilities and beautiful harmonies give much pleasure throughout the learning process.
If you would like to learn this piece with stylistically correct fingering and pedaling, check out my practice score with complete fingering and pedaling for easy practice of this colorful work which creates ideal articulation - articulate legato - almost without thinking.
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