Prelude in E minor, BWV855a

The piece opens with a rippling, continuous pattern of notes in the left hand, over which a slow-moving melody unfolds in long, sustained notes above. In its original keyboard form (BWV 855, the E minor prelude and fugue from Book I of the Well-Tempered Clavier), the prelude is brisk and toccata-like, built from constantly running figuration that passes between the hands.

The version most listeners encounter in the concert hall today is different: the Russian pianist and conductor Alexander Siloti reworked this material in the early 1900s, slowing the tempo, shifting it down to B minor, and turning the busy figuration into a hushed, murmuring accompaniment beneath a simple, aching melodic line. That arrangement, often just called "Bach-Siloti Prelude in B minor," is essentially an elegy, quiet, spacious, and unhurried from beginning to end.

Whether heard on organ, piano, or in orchestral dress, the piece has no contrasting middle section and no dramatic climax to wait for. Instead its interest lies in the steady, hypnotic pulse of the accompaniment and the way the melody seems to float free above it, arriving at a soft close that feels more like a sigh than an ending.

This prelude began life as part of Bach's Well-Tempered Clavier, Book I, a collection of preludes and fugues in every major and minor key that Bach assembled around 1722 as both teaching material and a demonstration of what a well-tuned keyboard could do. The E minor prelude and fugue, BWV 855, is one pair from that set. In the early twentieth century, the pianist Alexander Siloti arranged the prelude on its own, transposing it to B minor and slowing it into a hushed, meditative piece quite unlike Bach's brisk original; some sources also credit the organist Charles-Marie Widor with a related transcription. Bach never wrote or performed anything under the number BWV 855a himself. Its afterlife as a concert and encore piece, for piano, organ, or orchestra, belongs entirely to later arrangers who found in Bach's running keyboard figures the raw material for something quieter and more overtly emotional.