Bach Prelude and Fugue in E minor

The E minor prelude is a more extended piece, with a direction of Presto at bar 23, just over halfway through, speeding the piece to its conclusion. It is one of the eleven that originally appeared in Bach’s Clavierbüchlein (Little Clavier Book) for his eldest son, Wilhelm Friedemann, and is the most significantly altered in the WTC; originally it consisted only of the left-hand part. The fugue, unusually, is for only two voices that chase each other round in a perpetuum mobile.