This is my favourite prelude and fugue in book 1. The melody of the prelude is hauntingly beautiful; the first time I heard it I could hardly believe that it was by Bach. (He had, on the title page to his Inventions and Sinfonias, referred to the need for the keyboard player to develop a cantabile style of playing – absolutely essential here.) I prefer a legato touch for the fugue as well, which includes some of the most exquisite writing. The fugue is written in the enharmonic key of D sharp minor – 6 sharps replacing the 6 flats (and appearing at 6 o’clock on the Circle of Fifths). The key signature and shape of the subject of this fugue reflect the figure of the cross – the word for sharp in German is Kreuz (cross) and the historical origin for its notation in music derives from an X, the first letter of Christ in Greek.