Bach originally wrote this pair of pieces in C major, transposing them only when he needed to fill the C sharp major gap in his survey of all 24 keys. The prelude is bright, quick, and celebratory, with a fast, nattering element omnipresent either in the treble or the bass. The prelude leads almost directly into an oddly halting and irregular fugue subject that, despite its initial upswing, stumbles down the scale. Bach smoothes out the theme a bit during the free counterpoint that follows, and refuses to bring it back in its original form at the end.